.NET 4.0 - AccessViolationException and WndProc

Question

I have this code snippet:

internal class MTool : NativeWindow
{
    private const int WM_LBUTTONDOWN = 0x0201;
    public event TipDeactivateEventHandler Deactivate;

    protected override void WndProc(ref System.Windows.Forms.Message m)
    {           
        if( m.Msg == WM_LBUTTONDOWN )
        {
            if( this.Deactivate != null)
            {
                this.Deactivate();
            }
        }

        base.WndProc(ref m);
    }
}

When I run my program I get an AccessViolationException error at the line base.WndProc(ref m); and I don't know why.

Apparently this was ported over from .NET 2.0 to 4.0 and my theory is that there may be an alternate method used now in place of overriding WndProc. Is this case? If not why am I getting this exception?

Could you provide a bit more complete of a sample? At least showing how you're creating the MTool window and displaying it? I want to make sure my repro is close to yours. — Tim, Aug 20 '12 at 17:29
So you're not actually showing it any particular place, just creating the object? Don't you need to call CreateHandle or something like that for the NativeWindow to be useful? — Tim, Aug 20 '12 at 19:10
Have you tried putting a breakpoint on base.WndProc and seeing what is the value of m when exception is raised...also does it ever work for some m or does it throw exception the first time it is invoked.. — Amit Mittal, Aug 24 '12 at 10:21

score 7 · Accepted Answer · answered Aug 20 '12 at 19:39

7

I fixed it by adding this attribute above the method:

[System.Runtime.ExceptionServices.HandleProcessCorruptedStateExceptions]

Then surrounding the line where the exception occurs with a try/catch. I found this information here.

answered Aug 20 '12 at 19:39

Kyle V.

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Wouldn't it be better to work out what is causing the exception and try to fix that? – MikeKulls Aug 27 '12 at 01:05

score 2 · Answer 2 · answered Aug 20 '12 at 17:25

2

The documentation for WndProc shows demanding full-trust. have you tried that? e.g.:

[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
internal class MTool : NativeWindow
{
    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
    protected override void WndProc(ref Message m)
    {
//...

answered Aug 20 '12 at 17:25

Peter Ritchie

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Tried that, still getting the same exception. – Kyle V. Aug 20 '12 at 17:34

score 0 · Answer 3 · answered Aug 20 '12 at 18:04

0

I suspect there's something larger happening in your code. Based on your snippet, I would try:

Comment out the WndProc override, does this still repro by crashing somewhere else?
Make the WndProc only invoke "base.WndProc(ref msg)". Do you still get the same error? What's the callstack? Is there any more of your code deeper in the stack?
With the snippet as-is, is this only happening when WM_LBUTTONDOWN? When this throws that exception what is hooked to that Deactivate handler?

If these aren't practical to try, you probably need to update the snippet to explain better what you're trying to do.

answered Aug 20 '12 at 18:04

Joe Castro

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I strongly recommend against using the HPCSEAttribute to solve this. What's probably happening is your managed code is throwing an exception, or there's a marshalling exception (how did you build ptrStruct?). When you have code weaving in and out of native it's losing the context of the original exception and eventually surfacing as something that the CLR doesn't think it can catch. The attribute you've flagged as the correct answer is probably the difference in why this used to work, but there's a deeper problem that is being hidden. You really should debug this more. – Joe Castro Aug 21 '12 at 16:01

.NET 4.0 - AccessViolationException and WndProc

3 Answers3

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