WinForms: Why do I get InvalidCastException when showing folder browser dialog?

Posted by Marek on Stack Overflow See other posts from Stack Overflow or by Marek
Published on 2010-05-11T15:04:09Z Indexed on 2010/05/11 15:24 UTC
Read the original article Hit count: 329

Filed under:

imalloc

|

folderbrowserdialog

|

winforms

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c#

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.net-2.0

I am randomly getting InvalidCastException when showing FolderBrowserDialog and also many clients have reported this.

I have not been able to find anything relevant on the internet. Does anyone know what causes this/how to fix this?

My code:

        using (FolderBrowserDialog fbd = new FolderBrowserDialog())
        {
            fbd.ShowNewFolderButton = false;
            if (fbd.ShowDialog() == DialogResult.OK)

Stack trace:

Error: System.InvalidCastException: 
'Unable to cast object of type 'System.__ComObject' to type 'IMalloc'.'.

    Stack trace:    
at System.Windows.Forms.UnsafeNativeMethods.Shell32.SHGetMalloc(IMalloc[] ppMalloc)
at System.Windows.Forms.FolderBrowserDialog.GetSHMalloc()
at System.Windows.Forms.FolderBrowserDialog.RunDialog(IntPtr hWndOwner)
at System.Windows.Forms.CommonDialog.ShowDialog(IWin32Window owner)
at System.Windows.Forms.CommonDialog.ShowDialog()

EDIT: Additional information: I have been able to reproduce this only when running in VS2008 debugger.

When running out of debugger, it happens only very rarely (happened once or twice in 6 months) on my 64 bit Windows 7 and goes away after restart.

The clients are certainly not running the app in debugger so it is surely reproducible out of debugger.

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