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Getting Warning: "Variable" is used before it has been assigned a value.  Not sure why

Posted on 2008-10-14
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Last Modified: 2012-05-05
Getting Warning: "desktopArea" is used before it has been assigned a value.  Not sure why?


    Private Function GetScreen(ByVal X As Integer, ByVal Y As Integer, ByVal Width As Integer, ByVal Height As Integer) As Bitmap
        Dim hDeskDC As Integer
        Dim hTempDC As Integer
        Dim hBitmap As Integer
        Dim hTempBmp As Integer
        Dim desktopArea As Bitmap

        hDeskDC = CreateDC("DISPLAY", "", "", "")
        If hDeskDC Then
            hTempDC = CreateCompatibleDC(hDeskDC)
            If hTempDC Then
                hBitmap = CreateCompatibleBitmap(hDeskDC, Width, Height)
                If hBitmap Then
                    hTempBmp = SelectObject(hTempDC, hBitmap)
                    BitBlt(hTempDC, 0, 0, Width, Height, hDeskDC, X, Y, SRCCOPY)
                    desktopArea = Bitmap.FromHbitmap(New IntPtr(hBitmap))
                    DeleteObject(SelectObject(hTempDC, hTempBmp))
                End If
                DeleteDC(hTempDC)
            End If
            DeleteDC(hDeskDC)
        End If
        Return desktopArea
    End Function
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Question by:vaultworld
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3 Comments
 
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Mike Tomlinson earned 500 total points
ID: 22717679
Because it is possible that the If statements might fail and nothing ever gets assigned to "desktopArea".

You can fix the warning like this:

    Dim desktopArea As Bitmap = Nothing
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LVL 86

Expert Comment

by:Mike Tomlinson
ID: 22717716
For VB.Net 2005 (and above), you don't need a low level API wrapper like that though.

Just use one of the Graphics.CopyFromScreen() overloads:
http://msdn.microsoft.com/en-us/library/system.drawing.graphics.copyfromscreen(VS.80).aspx

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Author Closing Comment

by:vaultworld
ID: 31506166
Thanks again,
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