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Posted 2 Oct 2007
Licenced CPOL

Allow the User to Resize Controls at Runtime

, 2 Oct 2007
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Enable resizing of controls on a form at runtime with this class and two lines of code.


After searching the Web (including this site) for some simple code that would allow end users to resize controls at runtime, I finally concluded that there was not anything really effective yet really simple that I could even use as a base. I was perfectly willing to modify something to do what I wanted it to do, but most implementations were either buggy, or over-complicated, or just plain bad. I didn't find a single implementation that actually worked well.

Eventually, I decided to write my own. I did, and it was relatively simple (took about 2 hours to write), and it is very easy to use.


Basically, all we are trying to do here is create something that will allow the user to resize and move controls around at runtime, similar to how we developers are able to do at design-time. This code gives you (the developer) a fairly solid baseline from which you can create any custom behavior you want. Compared to other implementations I've found, this is the simplest and most effective I've seen.

Using the Code

It basically consists of a class that can be included anywhere in your project, and then a couple of lines of code to "hook" the class to the control that you want to enable for runtime resizing.

To start with, let's just look at how you "hook" the control (in other words, how the class is used to make any control resizable at runtime):

Public Class Form1

    Dim rc As ResizeableControl

    Private Sub Form1_Load(ByVal sender As System.Object, 
    ByVal e As System.EventArgs) Handles MyBase.Load

        rc = New ResizeableControl(pbDemo)

    End Sub

End Class

That's it! Simple enough, right?

You'll want to keep the rc variable at the form level so that it doesn't drop out of scope. When the form loads, just create an instance of ResizeableControl, pass it the control that you want to be resizable (a picturebox named pbDemo in this example, but it could be any control), and assign the new instance to the form level rc variable. If you wanted multiple controls to be resizable, you might create an array or collection of ResizeableControl objects at the form level.

Now let's take a look at the class itself:

Public Class ResizeableControl

    Private WithEvents mControl As Control
    Private mMouseDown As Boolean = False
    Private mEdge As EdgeEnum = EdgeEnum.None
    Private mWidth As Integer = 4
    Private mOutlineDrawn As Boolean = False

    Private Enum EdgeEnum
    End Enum

    Public Sub New(ByVal Control As Control)
        mControl = Control
    End Sub

    Private Sub mControl_MouseDown(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.MouseEventArgs) _
        Handles mControl.MouseDown

        If e.Button = Windows.Forms.MouseButtons.Left Then
            mMouseDown = True
        End If
    End Sub

    Private Sub mControl_MouseUp(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.MouseEventArgs) _
        Handles mControl.MouseUp

        mMouseDown = False
    End Sub

    Private Sub mControl_MouseMove(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.MouseEventArgs) _
    Handles mControl.MouseMove

        Dim c As Control = CType(sender, Control)
        Dim g As Graphics = c.CreateGraphics
        Select Case mEdge
            Case EdgeEnum.TopLeft
                g.FillRectangle(Brushes.Fuchsia, _
            0, 0, mWidth * 4, mWidth * 4)
                mOutlineDrawn = True
            Case EdgeEnum.Left
                g.FillRectangle(Brushes.Fuchsia, _
            0, 0, mWidth, c.Height)
                mOutlineDrawn = True
            Case EdgeEnum.Right
                g.FillRectangle(Brushes.Fuchsia, _
            c.Width - mWidth, 0, c.Width, c.Height)
                mOutlineDrawn = True
            Case EdgeEnum.Top
                g.FillRectangle(Brushes.Fuchsia, _
            0, 0, c.Width, mWidth)
                mOutlineDrawn = True
            Case EdgeEnum.Bottom
                g.FillRectangle(Brushes.Fuchsia, _
            0, c.Height - mWidth, c.Width, mWidth)
                mOutlineDrawn = True
            Case EdgeEnum.None
                If mOutlineDrawn Then
                    mOutlineDrawn = False
                End If
        End Select

        If mMouseDown And mEdge <> EdgeEnum.None Then
            Select Case mEdge
                Case EdgeEnum.TopLeft
                    c.SetBounds(c.Left + e.X, c.Top + e.Y, _
            c.Width, c.Height)
                Case EdgeEnum.Left
                    c.SetBounds(c.Left + e.X, c.Top, _
            c.Width - e.X, c.Height)
                Case EdgeEnum.Right
                    c.SetBounds(c.Left, c.Top, _
            c.Width - (c.Width - e.X), c.Height)
                Case EdgeEnum.Top
                    c.SetBounds(c.Left, c.Top + e.Y, _
            c.Width, c.Height - e.Y)
                Case EdgeEnum.Bottom
                    c.SetBounds(c.Left, c.Top, _
            c.Width, c.Height - (c.Height - e.Y))
            End Select
            Select Case True
                Case e.X <= (mWidth * 4) And _
            e.Y <= (mWidth * 4) 'top left corner
                    c.Cursor = Cursors.SizeAll
                    mEdge = EdgeEnum.TopLeft
                Case e.X <= mWidth 'left edge
                    c.Cursor = Cursors.VSplit
                    mEdge = EdgeEnum.Left
                Case e.X > c.Width - (mWidth + 1) 'right edge
                    c.Cursor = Cursors.VSplit
                    mEdge = EdgeEnum.Right
                Case e.Y <= mWidth 'top edge
                    c.Cursor = Cursors.HSplit
                    mEdge = EdgeEnum.Top
                Case e.Y > c.Height - (mWidth + 1) 'bottom edge
                    c.Cursor = Cursors.HSplit
                    mEdge = EdgeEnum.Bottom
                Case Else 'no edge
                    c.Cursor = Cursors.Default
                    mEdge = EdgeEnum.None
            End Select
        End If
    End Sub

    Private Sub mControl_MouseLeave(ByVal sender As Object, _
        ByVal e As System.EventArgs) _
        Handles mControl.MouseLeave

        Dim c As Control = CType(sender, Control)
        mEdge = EdgeEnum.None
    End Sub

End Class

That is all there is to it. You can download the example and give it a try, or just cut and paste the code from this article.

Points of Interest

As you can see, not a whole lot of code, but enough to make it work. I would suggest you use this as a starting point, and then customize it to suit your needs.

For example, the Fuchsia borders could be replaced with sizing handles and a dashed line around the control (like the .NET forms designer). You could also add the ability to grab a corner and stretch the control vertically and horizontally at the same time (again, like the .NET forms designer).

There is really no limit to what you could do, but at least this gives you a place to start, and it works pretty good "right out of the box".



  • 2nd October, 2007: Initial post


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Jesse Chunn
United States United States
Jesse Chunn was the Founder and CEO of Standard I-O, Inc. for 10 years until it was acquired in 2005. Since then he has spent most of his time providing strategic management to companies of all sizes. Most recently, he was the CIO of the Merchant Customer Exchange (MCX) and the Head of Merchant Strategy at CU Wallet. Jesse gets his thrills by coming up with elegant solutions to complicated problems, whether they be technology problems, business problems, or both (his favorite).

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Comments and Discussions

PraiseJust excellent! Pin
Member 1091169510-May-17 3:20
memberMember 1091169510-May-17 3:20 
Questionhow do I apply this to a user control which has an OnPaint event? Pin
Dr_HH23-Oct-16 9:06
memberDr_HH23-Oct-16 9:06 
AnswerRe: how do I apply this to a user control which has an OnPaint event? Pin
Dr_HH24-Oct-16 11:52
memberDr_HH24-Oct-16 11:52 
QuestionGrt work, Help with implementing this for 1column/2row TableLayoutPane Pin
Member 1124690920-Nov-15 5:24
memberMember 1124690920-Nov-15 5:24 
NewsC# Code Pin
Member 1169616816-May-15 14:51
memberMember 1169616816-May-15 14:51 
GeneralRe: C# Code Pin
Jesse Chunn23-May-15 17:42
memberJesse Chunn23-May-15 17:42 
Member 113501914-Jan-15 7:13
memberMember 113501914-Jan-15 7:13 
GeneralSome Updated Code Pin
Mellofax26-Jun-14 2:30
memberMellofax26-Jun-14 2:30 
SuggestionI have modified this quite heavily and made it much better...(Don't mean to be rude:D) Pin
Josh-Mason113-Sep-13 19:45
professionalJosh-Mason113-Sep-13 19:45 
GeneralRe: I have modified this quite heavily and made it much better...(Don't mean to be rude:D) Pin
Jesse Chunn4-Sep-13 10:51
memberJesse Chunn4-Sep-13 10:51 
GeneralRe: I have modified this quite heavily and made it much better...(Don't mean to be rude:D) Pin
Josh-Mason115-Sep-13 6:42
professionalJosh-Mason115-Sep-13 6:42 
GeneralRe: I have modified this quite heavily and made it much better...(Don't mean to be rude:D) Pin
Jesse Chunn20-Apr-14 10:26
memberJesse Chunn20-Apr-14 10:26 
QuestionPlease help adding drag to this great solution Pin
DutchLeo6-Apr-13 6:09
memberDutchLeo6-Apr-13 6:09 
AnswerRe: Please help adding drag to this great solution Pin
Josh-Mason114-Sep-13 9:30
professionalJosh-Mason114-Sep-13 9:30 
QuestionExtremely Helpful Pin
MathGeekQ25-Feb-13 9:29
memberMathGeekQ25-Feb-13 9:29 
QuestionHow to resize a veritcal scroll bar? Pin
Member 769168111-Oct-12 10:55
memberMember 769168111-Oct-12 10:55 
QuestionHelp to create a resizable button! Pin
Raha2823-Jun-12 23:15
memberRaha2823-Jun-12 23:15 
GeneralMy vote of 5 Pin
LanFanNinja24-Nov-11 18:35
memberLanFanNinja24-Nov-11 18:35 
GeneralMy vote of 5 Pin
Armando de la Torre18-Oct-11 9:04
memberArmando de la Torre18-Oct-11 9:04 
GeneralExcellent Article - Dragging Made Easy ! Pin
kasbaba6-Mar-10 23:36
memberkasbaba6-Mar-10 23:36 
AnswerFinal Version With Some Enhancements by Braian87b Pin
Member 378650823-Nov-09 7:31
memberMember 378650823-Nov-09 7:31 
GeneralNice Job. Pin
bollwerkj28-May-09 7:45
memberbollwerkj28-May-09 7:45 
QuestionSmall problem? Pin
PSU Steve27-Feb-09 3:11
professionalPSU Steve27-Feb-09 3:11 
GeneralAwesome! I tweaked it a bit... Pin
PSU Steve13-Feb-09 4:59
professionalPSU Steve13-Feb-09 4:59 
GeneralSmall enchancement Pin
Athmok17-Nov-08 4:26
memberAthmok17-Nov-08 4:26 

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