WM_DEVICECHANGE strange issue

Question

Hello experts Here I found how to listen to disk inserted or new drive added events: https://learn.microsoft.com/en-us/answers/questions/1555337/optical-drive-disc-inserted-event?source=docs And this is my code:

<SecurityPermission(SecurityAction.LinkDemand, Flags:=SecurityPermissionFlag.UnmanagedCode)>
Protected Overrides Sub WndProc(ByRef m As Message)
    If Button1.Enabled = False Then Exit Sub
    If m.Msg = WM_DEVICECHANGE AndAlso m.WParam.ToInt32() = DBT_DEVICEARRIVAL OrElse m.WParam.ToInt32() = DBT_DEVICEREMOVECOMPLETE OrElse m.WParam.ToInt32() = DBT_DEVNODES_CHANGED Then
        If m.LParam <> Nothing AndAlso Marshal.ReadInt32(m.LParam, 4) = DBT_DEVTYP_VOLUME Then RefreshButton_Click(Me, Nothing)
    End If
    MyBase.WndProc(m)
End Sub

But however, this line:

If Button1.Enabled = False Then Exit Sub

Will cause the form stop working normally and strange behavior, almost hang! Removing that single line will make it work as expected! Am I doing it correctly? And is this method safe at all or forget it? One more thing is that is it safe to use it on multiple forms? Thanks :)

Answer 1

Hi @Peter Volz ,

When Button1.Enabled = False, the code will exit Sub WndProc immediately when it reaches this line.

If you don't have a mandatory requirement for the state of Button1 in this method, you can delete this line.

Best Regards.

Jiachen Li

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