File Association in VB.NET

Download the demo project - 41.44 KB

Ever wanted to have your application open when the user opens a certain type of file? This is accomplished fairly easily by editing just a couple of registry keys.

How are Programs Associated?

The registry stores all the file type-app associations. Click on the Start Menu > Run > Type in 'regedit' > Ok. Now expand the HKEY_CLASSES_ROOT node. At the top of the window are all the extensions that your computer recognizes. Scroll down to .txt and click on it. Now look at the default value, it probably is 'txtfile'. Scrolling down the tree on the left, find the txtfile node. This contains all the information about any extensions that have their default value set to txtfile. Right now, we're just interested in opening the file, so open Shell > Open > Command. If your .txt files open with Notepad, then the default value should be "%SystemRoot%\system32\NOTEPAD.EXE %1".
%SystemRoot% is pretty self-explanatory, it's replaced by the folder that contains system32, which contains NOTEPAD.EXE.
%1 is a command-line argument to pass the program when a txtfile is opened. %1 is replaced by the file's location.

Step 1: Running Your Program When a .hello File is Opened

The first step is to get your application to open when a chosen extension (like .mp3) is double clicked in Windows Explorer. For this article, we'll use a file extension that shouldn't exist: .hello. To use this file type, create a new project called 'Hello World'. The idea in the included project article is this: a .hello file contains (in plain text) an adjective. When one is opened, a message box will pop-up and say, "Hello, (file contents) World". If you open the application manually, it will associate itself with the .hello extension. Therefore, before .hello files will be opened with the demo program by default, you must run it on its own.

Now we have to edit the registry just like you saw with the .txt extension. Use the following code to do this:

My.Computer.Registry.ClassesRoot.CreateSubKey(".hello").SetValue_
	("", "Hello", Microsoft.Win32.RegistryValueKind.String)
My.Computer.Registry.ClassesRoot.CreateSubKey_
	("Hello\shell\open\command").SetValue("", Application.ExecutablePath & _
	" ""%l"" ", Microsoft.Win32.RegistryValueKind.String)

What does all this do? If you don't understand My.Computer.Registry, here's a link to it on MSDN, or look below:

Code	What it does
`CreateSubKey(".hello")`	Creates a registry key in `ClassesRoot` for the .hello extension. Note that you must include the beginning period.
`.SetValue("", "Hello"...`	"" (Or `Nothing`) sets the default value of the key. "Hello" is like the "txtfile" we saw earlier, it tells which registry key contains the information about the .hello extension.
`CreateSubKey("Hello" & _ "\shell\open\command")`	This creates the "`Hello`" sub-key and the "`store\open\command`" subkey that is needed to store the path to the application that will open this file type.
`.SetValue("", Application.ExecutablePath & _ " ""%l"" ",...`	Again, "" tells the application to set the key's default value. `Application.ExecutablePath` tells the code to associate the currently running executable with this file type. `" ""%1"" "` passes the opened file's location to your program. The quotes around it are optional, but if you have more than one argument, you must put them around each.

Now run your application once. It will edit the registry. Your program is now associated with the .hello file!

Now let's say you want to create a file association for .txt in your program. You create the file association, but it still opens in Notepad. What's going on? There is another value that needs to be deleted located here:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.txt

The value name is 'Progid'. This will consist of a string value of the default program to open this filetype. If this value is present, you will not be able to associate anything with this particular filetype. You must delete the 'Progid' value in order for the association to work.

Thanks, Computer Masster!

Now to test it out. Open Notepad, type in an adjective, and save it as a .hello file (Make sure you don't accidentally save it as a .hello.txt file). Open the file in Windows Explorer. Your program will run! But nothing happens...

Step 2: Reading the File Contents

When the registry is set correctly and a file is opened in Windows Explorer, the file's path is passed as a command-line argument (if you think of an application as a function, then these are the parameters). To retrieve the arguments, you use My.Application.CommandlineArgs. It returns a ReadOnlyCollection(Of String). You can use My.Application.CommandlineArgs(0) to retrieve the file path.

Now, we have to display the message. More code for the Load event:

  msgbox("Hello, " & My.Computer.FileSystem.ReadAllText_
	(My.Application.CommandlineArgs(0)) & " World!")

Screenshot - VBFileAssociation2.gif

History

Date		Change
4/29/07		Article Submitted
4/30/07		Fixed up article so it fits on one page Updated demo project
5/8/07		Explained `My.Application.CommandLineArgs`
6/3/07		Added this tip
6/8/07		Fixed problems in the DLL
6/26/07		Changed the wordings in some phrases and fixed some errors in the examples
6/29/07		Fixed links No more sidescrolling!
6/19/09		Removed buggy library
8/10/10		Rewrote the sample applications so that they do not rely on the removed library and are fully open source Updated article

License

This article, along with any associated source code and files, is licensed under The Common Development and Distribution License (CDDL)

About the Author

Nick Rioux

United States

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Some additional questions...

Member 8117265

12:19 6 Feb '12

Hey, thanks a lot for this brilliant article. I just have a couple of questions regarding this to make sure I don't blow up the registry:

1) I have never worked with the registry before, but I do understand what's going on in this coding (without the details of how the registry knows where it has to look for its values, but that isn't that important to me). Would it be okay to associate the file type with my application every time the application is loaded (i.e. in the form load event)? I know that wouldn't be user friendly in case the user wants to open the files with a different program, but even if i do associate the file extension on every startup of my application, can that result in 'double registry entries'? Or will the existing entries be updated/replaced?

2. Of course it would be better to check if the file type is allready associated with my program first and then ask the user if he wants to associate it with my application if this is not the case. Is there a way to do that?

Thanks a lot for any help!!
Ibby

My vote of 5

Nasenbaaer

6:04 30 Jan '12

thanks to do it in VB.Net gave 6*
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My vote of 5

aaroncampf

7:33 1 Jul '11

Simple, Fast, and Effective!
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My vote of 4

stefangab95

21:26 22 Jun '11

Nice
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Cool But How do i set the icon for the file that opens?

XtanX

2:48 16 Oct '10

Cool But How do i set the icon for the file that opens?
Sign In·View Thread·Permalink	2.33/5 (3 votes)

Re: Cool But How do i set the icon for the file that opens?

IVAN PADRON

8:58 14 Jun '11

I have wrote this "associateFile" function as follow including Icon issue. I hope this can help
Regards

Public Class Form1
       Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        associateFile("HELLO", ".hello", "C:\myicon.ico", "My Hello File", Application.ExecutablePath)
    End Sub
 
Public Sub associateFile(ByVal mainKey As String, ByVal ext As String, ByVal iconPath As String, ByVal fileDescription As String, ByVal appPath As String)
        My.Computer.Registry.ClassesRoot.CreateSubKey(ext).SetValue("", mainKey, Microsoft.Win32.RegistryValueKind.String)
        My.Computer.Registry.ClassesRoot.CreateSubKey(mainKey).SetValue("", fileDescription, Microsoft.Win32.RegistryValueKind.String)
        My.Computer.Registry.ClassesRoot.CreateSubKey(mainKey &amp; "\shell\open\command").SetValue("", appPath &amp; " ""%l"" ", Microsoft.Win32.RegistryValueKind.String)
        My.Computer.Registry.ClassesRoot.CreateSubKey(mainKey &amp; "\DefaultIcon").SetValue("", iconPath, Microsoft.Win32.RegistryValueKind.ExpandString)
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        MsgBox("Hello, " & My.Computer.FileSystem.ReadAllText(My.Application.CommandLineArgs(0)) & " World!")
    End Sub
    End Class

Suggestion for next article.

Jalapeno Bob

7:59 12 Aug '10

This was a great article! Thank you. How about an article about command verbs? When you right-click on a file name, the context menu shows Open (usually naming a program) and Print, among other options. An article explaining how these work and how to add new ones should be of interest to those curious about the Windows Registry.
Sign In·View Thread·Permalink	5.00/5 (1 vote)

adding .dll

Emmery Chrisco

10:31 10 Aug '10

This is what I've been looking for. I don't mind that it's locked up in a dll. The question is, how do I add the .dll to my project? I went to project and added it as a reference, but it's dimmed out in the Solution Explorer.

I am using VB 2005 on Windows XP.

My app is a text editor. I want to give the users the option of making myapp the default application for .txt and .rtf files. The user will have a button to press to run the sub.

I've tried all the code above in various ways, but always get errors or no results at all.

Please help.

Re: adding .dll [modified]

Nickr5

14:10 10 Aug '10

I don't recommend using the dll as it was full of bugs and not all that well designed, which is why the download for it on its own was removed. Instead follow the instructions in the article and post your implementation here if you have problems.

Edit: I've submitted an update to the article that gets rid of the dll entirely and should act as a much better example.

File Association in VB.Net

modified on Tuesday, August 10, 2010 10:38 PM

Re: adding .dll

Emmery Chrisco

17:01 10 Aug '10

This is not creating any errors, but it's also not doing anything at all. The other snippet not included here, is chucked full of errors as soon as I paste it in my project.

    Private Sub Association_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Association.Click
        Dim rslt As MsgBoxResult
        rslt = MsgBox("Are you sure you want .txt and .rtf files to open with this application?", MsgBoxStyle.YesNo, "Change File Association?")
 
        If rslt = MsgBoxResult.Yes Then
            AssociateExtFile()
        ElseIf rslt = MsgBoxResult.No Then
            Exit Sub
        End If
    End Sub
 
    Private Sub AssociateExtFile()
 
        Try
 
            Dim extension As String = ".txt"
            Dim name As String = "textFile"
            Dim description As String = "text Formats File"
            Dim applicationPath As String = Environment.GetCommandLineArgs()(0)
            Dim iconPath As String = Path.Combine(Path.GetDirectoryName(applicationPath), "JWA.ico")
 
            AssociateFile(extension, name, description, iconPath, applicationPath)
 
        Catch ex As Exception
            MsgBox("Unable to associate file type" & ex.ToString)
        End Try
    End Sub
 

    Private Shared Sub AssociateFile(ByVal extension As String, ByVal name As String, ByVal description As String, ByVal iconPath As String, ByVal applicationPath As String)
 
        'Validate arguments
        If String.IsNullOrEmpty(extension) OrElse Not extension.StartsWith(".") Then Throw New ArgumentException("Extension must not be null, must also start with '.'", "extension")
        If String.IsNullOrEmpty(description) Then Throw New ArgumentException("description must not be null", "description")
 
        'Allow nothing to be passed for the icon file
        Dim iconFile As FileInfo = Nothing
        If iconPath IsNot Nothing Then
            iconFile = New FileInfo(iconPath)
            If Not iconFile.Exists Then Throw New ArgumentException("Icon file does not exist", "iconPath")
        End If
 
        Dim applicationFile As New FileInfo(applicationPath)
        If Not applicationFile.Exists Then Throw New ArgumentException("Application file does not exist", "applicationFile")
 
        'Create .extension value
        My.Computer.Registry.ClassesRoot.CreateSubKey(extension).SetValue("", name, Microsoft.Win32.RegistryValueKind.String)
 
        'Create filename value
        My.Computer.Registry.ClassesRoot.CreateSubKey((name & "\shell\open\command")).SetValue("", (applicationFile.FullName & " ""%l"" "), Microsoft.Win32.RegistryValueKind.String)
 
        'Set the description for the file name
        My.Computer.Registry.ClassesRoot.CreateSubKey(name).SetValue("", description)
 
        'Associate an icon if we were passed one
        If iconFile IsNot Nothing Then _
            My.Computer.Registry.ClassesRoot.CreateSubKey((name & "\DefaultIcon")).SetValue("", iconFile.FullName, Microsoft.Win32.RegistryValueKind.String)
 
    End Sub

Re: adding .dll

Nickr5

17:13 10 Aug '10

You may need to delete the Progid value located under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.txt Does using your code to associate an unused extension work? Does regedit show that everything has been changed correctly? File Association in VB.Net
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My vote of 2

jkljj

7:45 22 Feb '10

not very easy and wat if u want other stuff rather than text
Sign In·View Thread·Permalink	1.00/5 (1 vote)

Re: My vote of 2

Nickr5

16:37 10 Aug '10

For any format other than text, you would just read the file however you would normally read that type of file. For example, for an xml file you would just create an instance of a `System.Xml.XmlReader`. File Association in VB.Net
Sign In·View Thread·Permalink	5.00/5 (1 vote)

My vote of 2

ThePhilProject

1:08 3 Jan '10

Source Code Hidden in DLL!
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[My vote of 2] Souce code for all others: I can't belive you hid your code man, I gave this 5 for this, revoted to 2-

adudley256

22:32 4 Nov '09

 
Public Shared Sub Associate(ByVal Type As FileType, ByVal ExeFile As String, ByVal Optional ExtraCommands As String = Nothing)
    If ((((Type.Description <> Nothing) And (Type.Extension = Nothing)) And (Type.Icon = Nothing)) And (Type.Name = Nothing)) Then
        MyProject.Computer.Registry.ClassesRoot.CreateSubKey(Type.Extension).SetValue("", Type.Name, RegistryValueKind.String)
        MyProject.Computer.Registry.ClassesRoot.CreateSubKey((Type.Name & "\shell\open\command")).SetValue("", (ExeFile & " ""%l"" " & ExtraCommands), RegistryValueKind.String)
        MyProject.Computer.Registry.ClassesRoot.CreateSubKey(Type.Name).SetValue("", Type.Description)
        MyProject.Computer.Registry.ClassesRoot.CreateSubKey((Type.Name & "\DefaultIcon")).SetValue("", Type.Icon, RegistryValueKind.String)
    Else
        Dim innerException As New Exception(String.Concat(New String() { "Type.Name: ", Type.Name, ChrW(13) & ChrW(10) & "Type.Extension: ", Type.Extension, ChrW(13) & ChrW(10) & "Type.Description: ", Type.Description, ChrW(13) & ChrW(10) & "Type.Icon", Type.Icon }))
        Throw New Exception("One or more of the FileType's properties are invalid. See innerexception for deatails.", innerException)
    End If
End Sub

Re: [My vote of 2] Souce code for all others: I can't belive you hid your code man, I gave this 5 for this, revoted to 2-

adudley256

23:03 4 Nov '09

And this is the code done right:

''' <summary>
    ''' Associates the file extension passed with the application.
    ''' </summary>
    ''' <param name="extension">The extension.</param>
    ''' <param name="name">The name.</param>
    ''' <param name="description">The description.</param>
    ''' <param name="iconPath">The icon path.</param>
    ''' <param name="applicationPath">The application path.</param>
    Private Shared Sub AssociateFile(ByVal extension As String, ByVal name As String, ByVal description As String, ByVal iconPath As String, ByVal applicationPath As String)
 
        'Validate arguments
        If String.IsNullOrEmpty(extension) OrElse Not extension.StartsWith(".") Then Throw New ArgumentException("Extension must not be null, must also start with '.'", "extension")
        If String.IsNullOrEmpty(description) Then Throw New ArgumentException("description must not be null", "description")
 
        'Allow nothing to be passed for the icon file
        Dim iconFile As FileInfo = Nothing
        If iconPath IsNot Nothing Then
            iconFile = New FileInfo(iconPath)
            If Not iconFile.Exists Then Throw New ArgumentException("Icon file does not exist", "iconPath")
        End If
 
        Dim applicationFile As New FileInfo(applicationPath)
        If Not applicationFile.Exists Then Throw New ArgumentException("Application file does not exist", "applicationFile")
 
        'Create .extension value
        My.Computer.Registry.ClassesRoot.CreateSubKey(extension).SetValue("", name, Microsoft.Win32.RegistryValueKind.String)
 
        'Create filename value
        My.Computer.Registry.ClassesRoot.CreateSubKey((name & "\shell\open\command")).SetValue("", (applicationFile.FullName & " ""%l"" "), Microsoft.Win32.RegistryValueKind.String)
 
        'Set the description for the file name
        My.Computer.Registry.ClassesRoot.CreateSubKey(name).SetValue("", description)
 
        'Associate an icon if we were passed one
        If iconFile IsNot Nothing Then _
            My.Computer.Registry.ClassesRoot.CreateSubKey((name & "\DefaultIcon")).SetValue("", iconFile.FullName, Microsoft.Win32.RegistryValueKind.String)
 
    End Sub

And this is it being used:

Private Sub AssociateExtFile()
 
        Try
 
            Dim extension As String = ".test"
            Dim name As String = "testFile"
            Dim description As String = "test Formats File"
            Dim applicationPath As String = Environment.GetCommandLineArgs()(0)
            Dim iconPath As String = Path.Combine(Path.GetDirectoryName(applicationPath), "test.ico")
 
            AssociateFile(extension, name, description, iconPath, applicationPath)
 
        Catch ex As Exception
            MsgBox("Unable to associate file type" & ex.ToString)
        End Try
    End Sub

Re: [My vote of 2] Souce code for all others: I can't belive you hid your code man, I gave this 5 for this, revoted to 2-

Mr.Jinky

3:38 14 Aug '10

You got my 5 -= Really cool sig goes here =-
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Message Removed

Member 7724163

17:22 3 Mar '11

Message Removed
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Re: [My vote of 2]

adudley256

2:57 4 Mar '11

do you have access to write to the classess rout part of the registry? (try running your app as an administrator first) Normally any 'install' app needs to be promoted to Admin access.
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source code

DrKefir

14:48 28 Oct '09

Could you provide the source code of the Registry Actions.dll? Is the source code of your demo project that I just downloaded really up to date? It does not contain any of the actions from the "screen dump-picture of the form" from your article.
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Mailto association

asdfasdgf

8:25 29 Jun '09

So what would be used to associate a mailto link with an email program? URL:Mailto doesn't work. What would?
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how to remove association?

Rathin Mina

17:28 18 Mar '09

can you add a function to remove the association safely as well so that the previous program will take over registrations? Thanks!
Sign In·View Thread·Permalink	1.00/5 (3 votes)

NICE

MikeDaMan2594

15:56 14 Jan '09

This 100% Works! Its not even hard to follow! very clean, easy, and best of all working Thumbs up to you!
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I can't get it working

galaicra

12:14 20 Apr '08

Hi, I've tried your dll, with the following code:



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim fType As New FileType(".fitytest", "filetypetest", "Test of filetypes", "C:\Documents and Settings\Jesper\Skrivebord\free_icons\amc\Standard V.ico")

        DoAssociation.Associate(fType, Application.ExecutablePath, """%1""")

    End Sub

I've looked in my registry, and it seem to work, but when i open my .fifytest file, windows don't know which program to use. The program aren't shown either.
What have i done wrong?
- galaicra

Re: I can't get it working

Nickr5

5:59 21 Apr '08

`New FileType(".fitytest"` Try it without the preceding period. `New FileType("fitytest"` Fluent in VB, Attempts to speak C#, Python, English --- File Association in VB.Net Creating Custom Controls: Casino Royale
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