Using LINQ to Objects in Visual Basic

salysle

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Jun 4, 2008

CPOL

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This article provides an introduction to employing LINQ to Objects queries to support a simple WinForms application; the article addresses the construction of LINQ to Objects statements, and then goes on to describe how one might use LINQ to Objects within the context of an actual application.

Download source - 268 KB

Introduction

The demonstration project included with the article is a simple contact manager which may be used to capture and store information about a person’s contacts in address book format. This demonstration application uses LINQ to Objects to manage, query, and order the list of contacts maintained by the application. The demonstration application also includes a dummy contact file with a collection of test contacts.

Figure 1: Application Main Form

The application provides the following functionality:

Create a contact data file.
Add contacts to the contact data file.
Remove contacts from the contact data file.
Search for specific contacts by last name.
Create and edit details about the contact.

First Name
Middle Name
Last Name
Street
City
State
Zip Code
Home Phone
Work Phone
Cell Phone
Email Address

Save a contact data file.
Reopen a contact data file.
Navigate through all of the contacts in the contact data file.
View a list of all contacts in the contact data file.
Provide a Rolodex function (search by starting letter of last name).

Naturally, the approaches used within the application are representative of only one way of doing things; as with most things in the .NET world, there are several alternatives, and you can modify the code to work with the data using one of the other alternatives, if you prefer to do so.

Figure 2: Searching for a Contact by Last Name

Figure 3: Listing All Contacts (Edits to the grid are posted immediately to the List)

Figure 4: Rolodex Function

LINQ to Objects Statements

This section will discuss some of the common techniques used in LINQ to Objects statement construction. In a nutshell, LINQ to Objects provides the developer with the means to conduct queries against an in-memory collection of objects. The techniques used to query against such collections of objects are similar to but simpler than the approaches used to conduct queries against a relational database using SQL statements.

Anatomy of LINQ to Objects Statements

Example 1 – A Simple Select

This is an example of a very simple LINQ to Objects statement:

Public Sub Example1()

    Dim tools() As String = {"Tablesaw", "Bandsaw", "Planer", "Jointer", _
                             "Drill", "Sander"}

    Dim List = From t In tools _
                   Select t

    Dim sb As New StringBuilder()
    Dim s As String

    For Each s In List
        sb.Append(s + Environment.NewLine)
    Next

    MessageBox.Show(sb.ToString(), "Tools")

End Sub

In the example, an array of strings (tools) is used as the collections object to be queried using LINQ to Objects; the LINQ to Objects query is:

Dim List = From t In tools _
           Select t

In this example, an untyped variable “List” is created, and all of the items contained in the string array are added to this object. The types are inferred (implicitly typed). For example, “t” is a member of tools; since it is known that tools is a string array, the framework will infer that “t” is also a string. Of course, this is not all that terrific since you can just iterate through the array to do essentially the same thing; however, you can create more complex queries with LINQ to Objects, and then the value of the LINQ library becomes more apparent.

If you were to create a project, add this bit of code to a method, and run it; the results would look like this:

Figure 5: Query Results

Example 2 – Select with a Where Clause

The next example shows a LINQ to Objects query that incorporates a where clause. In this example, we start out with a collection of birds in the form of a string array; LINQ to Objects is used to query this string array to find and return a subset of the array in the form of all birds with names beginning with the letter “R”.

Public Sub Example2()

    Dim Birds() As String = {"Indigo Bunting", "Rose Breasted Grosbeak", _ 
                             "Robin", "House Finch", "Gold Finch", _
                             "Ruby Throated Hummingbird", _
                             "Rufous Hummingbird", "Downy Woodpecker"}

    Dim list = From b In Birds _
               Where b.StartsWith("R") _
               Select b

    Dim sb As New StringBuilder()
    Dim s As String

    For Each s In list
        sb.Append(s + Environment.NewLine)
    Next

    MessageBox.Show(sb.ToString(), "R Birds")

End Sub

If you were to run this query, the results would appear as follows (all birds with names beginning with the letter “R” are shown):

Figure 6: R Birds Query Results

Example 3 – Select with a Where Clause

In a slight variation to the previous query, this example looks for an exact match in its where clause:

Public Sub Example3()

    Dim Birds() As String = {"Indigo Bunting", "Rose Breasted Grosbeak", _ 
                             "Robin", "House Finch", "Gold Finch", _
                             "Ruby Throated Hummingbird", _
                             "Rufous Hummingbird", "Downy Woodpecker"}

    Dim list = From b In Birds _
               Where b = "Indigo Bunting" _
               Select b

    Dim sb As New StringBuilder()
    Dim s As String

    For Each s In list
        sb.Append(s + Environment.NewLine)
    Next

    MessageBox.Show(sb.ToString(), "Bunting Birds")

End Sub

Running this code will result in the display of this message box:

Figure 7: Bird Query Results

Example 4 – Generating an Ordered List

In this query, the list of birds is alphabetized (using “Order By b Ascending”):

Public Sub Example4()

    Dim Birds() As String = {"Indigo Bunting", "Rose Breasted Grosbeak", _ 
                             "Robin", "House Finch", "Gold Finch", _
                             "Ruby Throated Hummingbird", _
                             "Rufous Hummingbird", "Downy Woodpecker"}

    Dim list = From b In Birds _
               Order By b Ascending _
               Select b

    Dim sb As New StringBuilder()
    Dim s As String

    For Each s In list
        sb.Append(s + Environment.NewLine)
    Next

    MessageBox.Show(sb.ToString(), "Ordered Birds")

End Sub

Figure 8: Ordered Bird List Query Results

Example 5 – Working with a Custom Type

In this example, a typed list is created, populated, and then queried using LINQ to Objects.

Public Sub Example5()

    Dim parts = New List(Of Parts)

    Dim p1 As New Parts()
    p1.PartNumber = 1
    p1.PartDescription = "Cog"
    parts.Add(p1)

    Dim p2 As New Parts()
    p2.PartNumber = 2
    p2.PartDescription = "Widget"
    parts.Add(p2)

    Dim p3 As New Parts()
    p3.PartNumber = 3
    p3.PartDescription = "Gear"
    parts.Add(p3)

    Dim p4 As New Parts()
    p4.PartNumber = 4
    p4.PartDescription = "Tank"
    parts.Add(p4)

    Dim p5 = New Parts()
    p5.PartNumber = 5
    p5.PartDescription = "Piston"
    parts.Add(p5)

    Dim p6 As New Parts()
    p6.PartNumber = 6
    p6.PartDescription = "Shaft"
    parts.Add(p6)

    Dim p7 As New Parts()
    p7.PartNumber = 7
    p7.PartDescription = "Pulley"
    parts.Add(p7)

    Dim p8 As New Parts()
    p8.PartNumber = 8
    p8.PartDescription = "Sprocket"
    parts.Add(p8)


    Dim list = From p In parts _
                   Order By p.PartNumber Ascending _
                   Select p

    Dim sb As New StringBuilder()
    Dim pt As Parts

    For Each pt In parts
        sb.Append(pt.PartNumber.ToString() + ": " + _ 
                  pt.PartDescription.ToString() + _
                  Environment.NewLine)
    Next

    MessageBox.Show(sb.ToString(), "Parts List")

End Sub

The purpose of the query is merely to sort the parts list in the order of the part numbers. The results returned from this method are as follows:

Figure 9: Ordered Parts List Query

The Parts class used as the type behind the parts list is as follows:

Public Class Parts

    Private mPartNumber As Integer
    Private mPartDescription As String


    Public Sub New()
        ' nothing
    End Sub


    Public Sub New(ByVal partNum As Integer, ByVal partDesc As String)
        mPartNumber = partNum
        mPartDescription = partDesc
    End Sub


    Public Property PartNumber() As Integer
        Get
            Return mPartNumber
        End Get
        Set(ByVal value As Integer)
            mPartNumber = value
        End Set
    End Property


    Public Property PartDescription() As String
        Get
            Return mPartDescription
        End Get
        Set(ByVal value As String)
            mPartDescription = value
        End Set
    End Property


End Class

Example 6 – Searching a Typed List Using LINQ to Objects

In this example, a typed list is created (as in the previous example), populated, and then queried using LINQ to Objects. In this case, the query includes a where clause that only returns matches where the part description begins with the letter “S”:

Dim list = From p In parts _
           Where p.PartDescription.StartsWith("S") _
           Order By p.PartNumber Ascending _
           Select p

Dim sb As New StringBuilder()
Dim pt As Parts

For Each pt In list
    sb.Append(pt.PartNumber.ToString() + ": " _
    + pt.PartDescription.ToString() + _
    Environment.NewLine)
Next

MessageBox.Show(sb.ToString(), "Parts List")

Figure 10: Matching Parts Query Results

Example 7 – Searching a Typed List Using LINQ to Objects and Returning a Single Result

In this example, a typed list is created (as in the previous example), populated, and then queried using LINQ to Objects. In this case, a single result of type “Parts” is returned:

Dim matchingPart = (From m In list _
                            Where m.PartNumber.Equals(5) _
                            Select m).Single()

MessageBox.Show(matchingPart.PartDescription, "Matching Part")

The results of this query are shown in the next figure.

Figure 11: Returning a Single Result

The preceding examples were intended to provide a simple overview as to how to conduct some basic queries against collections using LINQ to Objects; there are certainly a great number of more complex operations that can be executed using similar procedures (grouping, joins, and selects into a new custom type, etc.).

Getting Started

There is a single solution included with this download, the solution contains a WinForms project called “LinqToObjectsVB”; this project contains two forms (the main form (frmContactBook) and a form used to display the total list of contacts (frmFullList)), a serializable class called ‘Contact’ (used to contain contact related data), and a class called ‘Serializer’ which contains two static methods used to serialize and deserialize the contact data (writing it to and reading it from a file).

If you open the attached project into Visual Studio 2008, you should see the following in the Solution Explorer:

Figure 12: Solution Explorer

Code: Contact.vb

The Contact class is the container class used to store all of the contact related data used in the application. Whilst this demonstration uses contact data, this could easily be replaced with something more useful to you.

The class begins with the normal and default imports:

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text

The next section contains the class declaration. Note that the class is declared as serializable; the Serializable attribute indicates that the class can be serialized.

<Serializable()> _
Public Class Contact

The region defined in the class declares the member variables used internally by the class; member variables exposed externally are made accessible through public properties.

#Region "Member Variables"

    Private mId As System.Guid
    Private mFirstName As String
    Private mMiddleName As String
    Private mLastName As String
    Private mStreet As String
    Private mCity As String
    Private mState As String
    Private mZip As String
    Private mEmail As String
    Private mHousePhone As String
    Private mWorkPhone As String
    Private mCellPhone As String
    Private mFax As String

#End Region

The next region of code in the class contains the constructors. Two constructors are defined. A default constructor creates a new instance of the class and assigns it an internal ID (as a GUID). The second constructor accepts an ID as an argument, and sets the contact’s internal ID to that value.

#Region "Constructor"

    Public Sub New()
        mId = Guid.NewGuid()
    End Sub


    Public Sub New(ByVal ID As System.Guid)
        mId = ID
    End Sub

#End Region

The last bit of code in this class is contained within the Properties region; this region contains all of the properties defined to access the member variables. Note that since the ID value is always set by the constructor, the property does not provide a public interface to set the GUID to a new value.

#Region "Properties"

    Public Property FirstName() As String
        Get
            Return mFirstName
        End Get
        Set(ByVal value As String)
            mFirstName = value
        End Set
    End Property


    Public Property MiddleName() As String
        Get
            Return mMiddleName
        End Get
        Set(ByVal value As String)
            mMiddleName = value
        End Set
    End Property


    Public Property LastName() As String
        Get
            Return mLastName
        End Get
        Set(ByVal value As String)
            mLastName = value
        End Set
    End Property


    Public Property Street() As String
        Get
            Return mStreet
        End Get
        Set(ByVal value As String)
            mStreet = value
        End Set
    End Property


    Public Property City() As String
        Get
            Return mCity
        End Get
        Set(ByVal value As String)
            mCity = value
        End Set
    End Property


    Public Property State() As String
        Get
            Return mState
        End Get
        Set(ByVal value As String)
            mState = value
        End Set
    End Property


    Public Property ZipCode() As String
        Get
            Return mZip
        End Get
        Set(ByVal value As String)
            mZip = value
        End Set
    End Property


    Public Property Email() As String
        Get
            Return mEmail
        End Get
        Set(ByVal value As String)
            mEmail = value
        End Set
    End Property


    Public Property HousePhone() As String
        Get
            Return mHousePhone
        End Get
        Set(ByVal value As String)
            mHousePhone = value
        End Set
    End Property


    Public Property WorkPhone() As String
        Get
            Return mWorkPhone
        End Get
        Set(ByVal value As String)
            mWorkPhone = value
        End Set
    End Property


    Public Property CellPhone() As String
        Get
            Return mCellPhone
        End Get
        Set(ByVal value As String)
            mCellPhone = value
        End Set
    End Property


    Public Property Fax() As String
        Get
            Return mFax
        End Get
        Set(ByVal value As String)
            mFax = value
        End Set
    End Property


#End Region

End Class

That concludes the description of the ‘Contact’ class.

Code: Main Application Form (frmContactBook.vb)

The is the main form of the application; much of the code provides the framework for the application, and does not really pertain to LINQ to Objects. However, all of the code will be described herein to provide a proper context.

The contact application’s main form contains the following controls:

File

New
Open
Save
Save As
Exit

Contacts

Add Contact
Remove Contact
List All Contacts

Toolbar

Add
Remove
Find by Last Name
Save Data
Navigate to Previous Contact
Navigate to Next Bird Contact
Exit Application

Split Container Left Hand Side

Alphabet List
Alphabetized Names List

Split Container Right Hand Side
First name text box control
Middle name text box control
Last name text box control
Street text box control
City text box control
State text box control
Zip code text box control
Home phone number text box control
Work phone number text box control
Cell number text box control
Fax number text box control
Email address text box control

Figure 13: frmContactBook.vb

The class begins with the normal and default imports:

Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Linq
Imports System.Text
Imports System.Windows.Forms

The next section contains the class declaration.

Public Class frmContactBook

The next region defined in the class declares the member variables used internally by the class; member variables exposed externally are made accessible through public properties. The comment adjacent to each declaration describes its purpose.

#Region "Member Variables"

    Private contacts As New List(Of Contact)    ' create a typed list of contacts
    Private currentContact As Contact           ' create a single contact instance
    Private currentPosition As Integer          ' used to hold current position
    Private currentFilePath As String           ' file path to current contact file
    Private dirtyForm As Boolean                ' keep track of dirty forms

#End Region

The next region of code in the class contains the constructor. Upon initialization, the application creates a new contact data list, creates a new contact data object, sets the current position indicator to zero, and sets the dirtyForm boolean to False.

#Region "Constructor"

    ''' <summary>
    ''' Constructor - create a new instance of
    ''' the contact list and setup the local
    ''' member variables
    ''' </summary>
    ''' <remarks></remarks>
    Public Sub New()

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.

        contacts = New List(Of Contact)
        currentContact = New Contact()
        contacts.Add(currentContact)
        currentPosition = 0
        dirtyForm = False

    End Sub

#End Region

The next code region is called ‘Toolstrip Event Handlers’; the first event handler in this region is the Click event handler for the Add button; this method merely calls the menu control’s Click event handler, and the code contained in that event handler adds a new contact to the current contact data.

#Region "Toolstrip Event Handlers"

    ''' <summary>
    ''' Add a new contact to the current contact list
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub tsbAddRecord_Click(ByVal sender As System.Object, _
                                   ByVal e As System.EventArgs) _
                                   Handles tsbAddRecord.Click

        Me.addToolStripMenuItem_Click(Me, New EventArgs())

    End Sub

The next Click event handler is used to remove the current contact from the contact list when the user clicks the toolstrip’s Remove Record button; again, this method merely calls the matching menu item function.

''' <summary>
''' Remove the current contact from the contact list
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub tsbRemoveRecord_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles tsbRemoveRecord.Click

    Me.removeToolStripMenuItem_Click(Me, New EventArgs())

End Sub

The next handler is used to search for a specific contact using the contact’s last name. The code uses a LINQ to Objects query in order to find the first instance of a matching contact with that last name. The handler uses the Search Term text box control on the toolstrip to capture the last name, and it uses the Search button to execute the search. The code is annotated to describe what is going on in this method.

''' <summary>
''' Find a contact by searching the list
''' for a matching last name
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub tsbFindContact_Click(ByVal sender As System.Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles tsbFindContact.Click

    ' return if the search term was not provided
    If (String.IsNullOrEmpty(tspSearchTerm.Text)) Then

        MessageBox.Show("Enter a last name in the space proved.", _
                        "Missing Search Term")
        Return

    End If


    Try
        ' using linq to objects query to get first matching name
        Dim foundGuy = _
                    (From contact In contacts _
                     Where contact.LastName = tspSearchTerm.Text _
                     Select contact).FirstOrDefault()

        ' set the current contact to the found contact
        currentContact = foundGuy
        currentPosition = contacts.IndexOf(currentContact)

        ' update the display by loading the 
        ' found contact
        LoadCurrentContact()

        ' clear the search term textbox and return
        tspSearchTerm.Text = String.Empty
        Return

    Catch

        MessageBox.Show("No matches were found", "Search Complete")

    End Try

End Sub

The next handler saves the current contact list; this handler just calls the matching menu Click event handler.

''' <summary>
''' Save the current contact list
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub tsbSave_Click(ByVal sender As System.Object, _
                          ByVal e As System.EventArgs) _
                          Handles tsbSave.Click

    Me.saveStripMenuItem_Click(Me, New EventArgs())

End Sub

The next handler is used to navigate back one contact from the current position of the displayed contact. If the contact as at the lower limit, the button click is ignored.

''' <summary>
''' Navigate back to the previous record
''' if not at the lower limit
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub tsbNavBack_Click(ByVal sender As System.Object, _
                             ByVal e As System.EventArgs) _
                             Handles tsbNavBack.Click

    ' capture form changes and plug them
    ' into the current contact before
    ' navigating off the contact
    SaveCurrentContact()

    ' don't exceed the left limit
    If (currentPosition <> 0) Then
        currentPosition -= 1
        currentContact = contacts(currentPosition)
        LoadCurrentContact()
    End If

End Sub

The next handler is used to navigate forward one contact from the current position of the displayed contact. If the contact is at the upper limit, the button click is ignored.

''' <summary>
''' Navigate to the next record if
''' not at the upper limit
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub tsbNavForward_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) _
                                Handles tsbNavForward.Click

    ' capture form changes and plug them
    ' into the current contact before
    ' navigating off the contact
    SaveCurrentContact()

    ' don't exceed the right limit
    If (currentPosition < contacts.Count - 1) Then
        currentPosition += 1
        currentContact = contacts(currentPosition)
        LoadCurrentContact()
    End If

End Sub

The next handler is used to exit the application. This handler merely calls the matching menu item Click event handler.

    ''' <summary>
    ''' Exit the application
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub tsbExit_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles tsbExit.Click

        Me.exitToolStripMenuItem_Click(Me, New EventArgs())

    End Sub


#End Region

The next region contains the menu item Click event handlers. The next menu item Click event handler creates a new contact list; before following through with the creation of the new contact list, this handler checks to see if the current form is dirty to allow the user the opportunity to save before closing the current list. Following that, the contact list is replaced with a new contact list and the form’s controls are cleared.

#Region "Menu Item Click Event Handler"

    ''' <summary>
    ''' Create a new contact list and clear
    ''' the contact form
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub newToolStripMenuItem_Click(ByVal sender As System.Object, _
                                           ByVal e As System.EventArgs) _
                                           Handles newToolStripMenuItem.Click

        ' check to see if the form has been editted
        If dirtyForm = True Then

          If (MessageBox.Show(Me, "You have not saved the current contact data; " + _
                             "would you like to save before starting a new " + _
                             "contact database?", "Save Current Data",  
                MessageBoxButtons.YesNo) = _
                System.Windows.Forms.DialogResult.Yes) Then

                ' display the save dialog if the contact list is dirty
                saveAsMenuItem_Click(Me, New EventArgs())

            End If

        Else

            ' discard the contact list and 
            ' start new document
            contacts = New List(Of Contact)
            ClearScreen()

        End If

    End Sub

The next event handler is used to open a contacts file. Again, the handler checks for a dirty form and provides the user with an opportunity to save if the form is dirty. A separate Open method is called to handle the actual file opening operation.

''' <summary>
''' Open an existing contact file
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub openToolStripMenuItem_Click(ByVal sender As System.Object, _
                                        ByVal e As System.EventArgs) _
                                        Handles openToolStripMenuItem.Click

    ' give the user an opportunity to save the current
    ' contact list if the data has been edited
    If dirtyForm = True Then

      If (MessageBox.Show(Me, "You have not saved the current contact data; " + _
                         "would you like to save before opening a different " + _
                         "contact database?", "Save Current Data", 
            MessageBoxButtons.YesNo) = _
            System.Windows.Forms.DialogResult.Yes) Then

            saveAsMenuItem_Click(Me, New EventArgs())

        End If

    Else

        ' call the open function to open the file
        Open()

    End If

End Sub

The Save menu item is used to save the current contacts file to disk; the function first calls a “SaveCurrentContact”, which is used to save the current contact to the current contact data list. Next, the function uses the Save File Dialog to capture a file name if none is currently set to the “currentFilePath” variable, or, if the variable is set, it saves the file using that file path. The file is actually saved to disk when the call to serialize the file is made.

''' <summary>
''' Save the current contact list
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub saveStripMenuItem_Click(ByVal sender As System.Object, _
                                    ByVal e As System.EventArgs) _
                                    Handles saveStripMenuItem.Click

    ' save the current form data to the list
    SaveCurrentContact()

    ' if the file path is not set, open the
    ' save file dialog
    If String.IsNullOrEmpty(currentFilePath) Then

        Dim SaveFileDialog1 As New SaveFileDialog()

        Try
            SaveFileDialog1.Title = "Save CON Document"
            SaveFileDialog1.Filter = "CON Documents (*.con)|*.con"

            If (SaveFileDialog1.ShowDialog() = _
                System.Windows.Forms.DialogResult.Cancel) Then
                Return
            End If
        Catch
            Return
        End Try

        currentFilePath = SaveFileDialog1.FileName

    End If

    ' make sure the file path is not empty
    If String.IsNullOrEmpty(currentFilePath) Then
        Return
    End If

    ' persist the contacts file to disk
    Serializer.Serialize(currentFilePath, contacts)

    ' tell the user the file was saved
    MessageBox.Show("File " + currentFilePath + " saved.", "File Saved.")

    ' everything is saved, set the dirtyform
    ' boolean to false
    dirtyForm = False

End Sub

The next bit of code is used to support the “Save As” menu item; the call is similar to the previous Save method, but straight opens the Save File Dialog to permit the user to name or rename the file.

''' <summary>
''' Save the current contact data as a file
''' under a new name
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub saveAsMenuItem_Click(ByVal sender As System.Object, _
                                 ByVal e As System.EventArgs) _
                                 Handles saveAsMenuItem.Click

    ' save the current form data to the contact list
    SaveCurrentContact()

    ' create and show the save file dialog
    Dim SaveFileDialog1 As New SaveFileDialog()

    Try
        SaveFileDialog1.Title = "Save CON Document As"
        SaveFileDialog1.Filter = "CON Documents (*.con)|*.con"

        If (SaveFileDialog1.ShowDialog() = _
            System.Windows.Forms.DialogResult.Cancel) Then
            Return
        End If
    Catch
        Return
    End Try

    currentFilePath = SaveFileDialog1.FileName

    ' make sure the file path is set
    If String.IsNullOrEmpty(currentFilePath) Then
        Return
    End If

    ' persist the contacts file to disk
    Serializer.Serialize(currentFilePath, contacts)

    ' tell the user the file was saved
    MessageBox.Show("File " + currentFilePath + " saved.", "File Saved.")

    ' everything is saved, set the dirtyform
    ' boolean to false
    dirtyForm = False

End Sub

The next method exits the application but checks the dirtyForm boolean prior to exiting, to give the user a chance to save their edits.

''' <summary>
''' Exit the application
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub exitToolStripMenuItem_Click(ByVal sender As System.Object, _
                                        ByVal e As System.EventArgs) _
                                        Handles exitToolStripMenuItem.Click

    If dirtyForm = True Then

      If (MessageBox.Show(Me, "You have not saved the current contact data; " + _
                         "would you like to save before exiting?", "Save Current 
                         Data", _
                         MessageBoxButtons.YesNo) = 
                         System.Windows.Forms.DialogResult.Yes) Then

            tsbSave_Click(Me, New EventArgs())

        End If

    Else

        Application.Exit()

    End If

End Sub

The next method is used to add a new contact to the current list of contacts; this method saves the current contact to the open list of contacts, creates a new contact, and adds it to the list of contacts, clears the form, and marks the form as dirty:

''' <summary>
''' Add a new contact to the current
''' contact list
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub addToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As 
System.EventArgs) Handles addToolStripMenuItem.Click

    SaveCurrentContact()
    currentContact = New Contact()
    contacts.Add(currentContact)
    ClearScreen()
    dirtyForm = True

End Sub

The next method removes the current contact from the list and updates the display.

''' <summary>
''' Remove the current contact from the
''' contact list and update the display
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub removeToolStripMenuItem_Click(ByVal sender As System.Object, _
                                          ByVal e As System.EventArgs) _
                                          Handles removeToolStripMenuItem.Click

    ' make sure there are records
    If contacts.Count = 0 Then

        ' remove the current record
        contacts.Remove(currentContact)

        ' check to see if the current
        ' position is at the limit
        ' and move up or down
        ' as required
        If (currentPosition = 0) Then

            currentPosition += 1

        End If

    Else

        currentPosition -= 1

        ' reload the current contact
        ' from the new position
        currentContact = contacts(currentPosition)
        LoadCurrentContact()

        ' dirty the form since a 
        ' record was removed
        dirtyForm = True

    End If

End Sub

The next method is used to open a separate form displaying all of the contacts in a DataGridView control. This method constructs an ordered list, and passes it to a new instant of the “frmFullList” class which binds the grid control to the list in its constructor.

    ''' <summary>
    ''' Display a list of all the contacts in a data grid
    ''' view control
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub listAllContactsToolStripMenuItem_Click(ByVal sender As System.Object, 
                                                       ByVal e As System.EventArgs) _
                                                       Handles 
                                               listAllContactsToolStripMenuItem.Click

        ' use linq to objects to create a list of contacts 
        ' ordered by the contact's last name, first name,
        ' and middle name
        Dim orderedCons = _
            (From contact In contacts _
             Order By contact.LastName Ascending, _
             contact.FirstName Ascending, _
             contact.MiddleName Ascending _
             Select contact)

        ' create an instance of the full list form and pass it's
        ' constructor the list converted to a List
        Dim f As New frmFullList(orderedCons.ToList())
        f.Show()

    End Sub

#End Region

The next region contains a garbage can collection of other methods, maintained in a region titled “Housekeeping”:

#Region "Housekeeping"

The first method contained in this section is used to clear all of the text boxes used to display contact information. This is called anytime the current contact is changed, to prevent remnants of one contact appearing in the display of a replacement contact.

''' <summary>
''' Clear all of the fields in the form
''' </summary>
''' <remarks></remarks>
Private Sub ClearScreen()

    txtFirstName.Text = String.Empty
    txtMiddleName.Text = String.Empty
    txtLastName.Text = String.Empty
    txtStreet.Text = String.Empty
    txtCity.Text = String.Empty
    txtState.Text = String.Empty
    txtZipCode.Text = String.Empty
    txtHousePhone.Text = String.Empty
    txtWorkPhone.Text = String.Empty
    txtCellPhone.Text = String.Empty
    txtFax.Text = String.Empty
    txtEmailAddress.Text = String.Empty

    tslViewWho.Text = String.Empty

End Sub

The next method is used to load information contained in the current contact into the controls used to display contact information.

''' <summary>
''' Load the current contact into the form fields
''' </summary>
''' <remarks></remarks>
Private Sub LoadCurrentContact()

    ' update the form fields
    txtFirstName.Text = currentContact.FirstName
    txtMiddleName.Text = currentContact.MiddleName
    txtLastName.Text = currentContact.LastName
    txtStreet.Text = currentContact.Street
    txtCity.Text = currentContact.City
    txtState.Text = currentContact.State
    txtZipCode.Text = currentContact.ZipCode
    txtHousePhone.Text = currentContact.HousePhone
    txtWorkPhone.Text = currentContact.WorkPhone
    txtCellPhone.Text = currentContact.CellPhone
    txtFax.Text = currentContact.Fax
    txtEmailAddress.Text = currentContact.Email

    ' display the current user in the status bar
    tslViewWho.Text = "Now Viewing " + txtFirstName.Text + " " + txtLastName.Text

End Sub

The next method captures all of the information currently on the form for the current contact, and writes it into the current contact’s properties. This is called whenever a contact is changed so that all edits to an existing contact are held within the local list until it can be written to disk. The method further updates the order of the contacts, and updates the contact list and displayed contact.

''' <summary>
''' Save the form data to the current
''' contact, reorder the contact list,
''' and update the display
''' </summary>
''' <remarks></remarks>
Private Sub SaveCurrentContact()

    If (Not String.IsNullOrEmpty(txtFirstName.Text) And _
        (Not String.IsNullOrEmpty(txtLastName.Text))) Then

        Try

            ' get all of the textbox values and
            ' plug them into the current contact object
            currentContact.FirstName = txtFirstName.Text
            currentContact.MiddleName = txtMiddleName.Text
            currentContact.LastName = txtLastName.Text
            currentContact.Street = txtStreet.Text
            currentContact.City = txtCity.Text
            currentContact.State = txtState.Text
            currentContact.ZipCode = txtZipCode.Text
            currentContact.HousePhone = txtHousePhone.Text
            currentContact.WorkPhone = txtWorkPhone.Text
            currentContact.CellPhone = txtCellPhone.Text
            currentContact.Fax = txtFax.Text
            currentContact.Email = txtEmailAddress.Text


            ' reorder the contacts by last, first, and
            ' middle name to keep everything in correct
            ' alphabetical order
            Dim orderedContacts = _
                    (From contact In contacts _
                     Order By contact.LastName Ascending, _
                     contact.FirstName Ascending, _
                     contact.MiddleName Ascending _
                     Select contact).ToList()

            ' set the contacts list to the newly
            ' ordered list
            contacts = orderedContacts

            ' update the current position index value
            currentPosition = contacts.IndexOf(currentContact)

            ' reload the current contact
            LoadCurrentContact()

        Catch ex As Exception

            MessageBox.Show(ex.Message, "Error")

        End Try

    End If

End Sub

The next method is used to open and deserialize an existing contact file, making it available for edit and viewing within the application.

''' <summary>
''' Open an existing contacts file
''' </summary>
''' <remarks></remarks>
Public Sub Open()

    Dim OpenFileDialog1 As New OpenFileDialog()
    OpenFileDialog1.Title = "Open con Document"
    OpenFileDialog1.Filter = "CON Documents (*.con)|*.con"

    If OpenFileDialog1.ShowDialog() = System.Windows.Forms.DialogResult.Cancel 
    Then
        Return
    End If

    currentFilePath = OpenFileDialog1.FileName

    If String.IsNullOrEmpty(currentFilePath) Then
        Return
    End If

    If System.IO.File.Exists(currentFilePath) = False Then
        Return
    End If

    ' deserialize file content into contacts 
    ' list to make it available to the application
    contacts = Serializer.Deserialize(currentFilePath)

    ' alphabetize the contact list
    ' by last, first, and middle name and
    ' push the results into a List
    Dim orderedContacts = _
                (From contact In contacts _
                 Order By contact.LastName Ascending, _
                  contact.FirstName Ascending, _
                  contact.MiddleName Ascending _
                 Select contact).ToList()

        ' set the contacts list to the newly
        ' ordered list
        contacts = orderedContacts

        ' Load contacts at position zero
        ' if contacts list is not empty
        If contacts.Count > 0 Then
            currentContact = contacts.ElementAt(0)
            LoadCurrentContact()
            dirtyForm = False
        End If


    End Sub

#End Region

The final region in this form class is used to handle the listbox control events. These controls are used to provide a Rolodex sort of functionality to the application. The listbox controls are loaded into the left hand split panel’s panel. The top listbox control displays all of the letters in the alphabet, whilst the lower listbox control is used to display all matching last names beginning with the letter selected in the upper listbox.

#Region "Listbox Event Handlers"

The first function handles the selected index changed event for the upper listbox containing all of the letters of the alphabet. When a new letter is selected, this method uses a simple LINQ to Objects query to find all contacts with last names beginning with the selected letter. The lower listbox is then cleared, and then the matches are formatted into a string, showing the contact’s last name, first name, and middle name, and each formatted string is then added to the lower listbox control.

''' <summary>
''' Find all last names starting with the selected letter
''' and display that list of matching names in the names
''' list box
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub lstAlphas_SelectedIndexChanged(ByVal sender As System.Object, _
                                           ByVal e As System.EventArgs) _
                                           Handles lstAlphas.SelectedIndexChanged

    ' store the selected letter as a local variable
    Dim alpha As String = lstAlphas.SelectedItem.ToString()

    ' make sure the contact list is not empty
    If contacts.Count > 0 Then

        Try

            ' use linq to objects query to find
            ' last names matching the selected
            ' letter of the alphabet
            Dim alphaGroup = _
                From contact In contacts _
                Where contact.LastName.ToUpper().StartsWith(alpha) _
                Select contact

            ' clear out any names from the
            ' existing list
            lstNames.Items.Clear()

            ' add the short list of matching
            ' names to the list box
            Dim con As Contact
            For Each con In alphaGroup
                lstNames.Items.Add(con.LastName + ", " + _
                    con.FirstName + " " + con.MiddleName)
            Next

            ' if no matches were found, tell the user
            ' with a note in the box
            If (alphaGroup.Count < 1) Then
                lstNames.Items.Clear()
                lstNames.Items.Add("No matches were found")
            End If

        Catch
            lstNames.Items.Clear()
            lstNames.Items.Add("No matches were found")
        End Try

    End If

End Sub

The names listbox SelectedIndexChanged event is handled in the next block of code. In it, the name string (last name, first name, middle name) is parsed and used in a LINQ to Objects query used to return a list of all matching names; the first found name is displayed in the contact form, and the index position is updated to support list navigation.

    ''' <summary>
    ''' Display the selected contact's information in the
    ''' contact form's fields
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub lstNames_SelectedIndexChanged(ByVal sender As System.Object, _
                                                  ByVal e As System.EventArgs) _
                                                  Handles lstNames.SelectedIndexChanged

        ' if there were no matches found, return from this function
        If (lstNames.SelectedItem.ToString().Trim() = "No matches were found") Then
            Return
        End If

        ' variables to hold parts of the name as search terms
        Dim first As String = String.Empty
        Dim middle As String = String.Empty
        Dim last As String = String.Empty

        ' get the last name
        Dim arr() As String = lstNames.SelectedItem.ToString().Trim().Split(",")
        last = arr(0).Trim()

        ' get the first name
        Dim arr2() As String = arr(1).ToString().Trim().Split(" ")
        first = arr2(0).Trim()

        ' get the middle name
        Try
            middle = arr2(1).Trim()
        Catch
            ' no middle name
        End Try

        Try
            ' using linq to objects query to get a collection of matching names
            ' when all three names match
            Dim foundGuy = _
                        (From contact In contacts _
                         Where contact.FirstName.Equals(first) And _
                               contact.LastName.Equals(last) And _
                               contact.MiddleName.Equals(middle) _
                         Select contact).FirstOrDefault()

            ' set the current contact to the first found
            ' contact
            currentContact = foundGuy

            ' update the index position used to maintain
            ' the current position within the list
            currentPosition = contacts.IndexOf(currentContact)

            ' reload the current contact and return
            LoadCurrentContact()
            Return

        Catch ex As Exception
            MessageBox.Show(ex.Message, "Error Encountered")
        End Try

    End Sub

#End Region

End Class

Code: frmFullList.vb

This form class contains a DataGridView control and a constructor which accepts a contact list (List(Of Contact)) as an argument. Upon initialization, the list is bound to the DataGridView control.

Changes made by edits in the grid are maintained in the contact list.

There is not much code; it is presented here in its entirety:

Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Linq
Imports System.Text
Imports System.Windows.Forms

Public Class frmFullList

    Public Sub New(ByVal cons As List(Of Contact))

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' display the contact list in the
        ' data grid view control
        dgvFullList.DataSource = cons


    End Sub

End Class

Summary

The article shows some simple examples of LINQ to Objects queries used in support of a sample application. LINQ to Objects may be used to generate more complex queries than are shown in the example; however, those demonstrated herein are representative of some of the more common tasks that one might choose to do within a similar application. Much of the code in the demonstration project was provided as a framework for the application, and was necessary to create an environment useful for testing some simple LINQ to Objects based queries.