VB.Net Metafile generates error ("A generic error occurred in GDI+")

Question

I would like get a little help from you. I am working on a diagram creator which can be called more than once. The diagram every time is different than the earlier version but I would like to use the same filename. The problem is that when I click on the button the program is showing the diagram form with the diagram in the picturebox but if the form is closed and I am clicking on the button again I have an error ("A generic error occurred in GDI+"). I think the mf.dispose() does not close the file and it opened. What do you think what is the problem, how can I solve it?

Main Form:

Imports System.Runtime.InteropServices
Imports System.Drawing.Imaging

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Diagram.create_diagram()
        Diagram_FORM.PictureBox1.Image = New Metafile("c:\temp\test.wmf")
        Diagram_FORM.Show()
    End Sub

Diagram Class:


Imports System.Runtime.InteropServices
Imports System.Drawing.Imaging

Class Diagram

Public Sub create_diagram()
        Dim diagram_width As Integer = 600
        Dim diagram_Height As Integer = 600
        Dim filename As String = "c:\temp\test.wmf"
        
        Dim gr As Graphics
        gr = Graphics.FromImage(New Bitmap(diagram_width, diagram_Height))

        ' Make a Graphics object so we can use its hDC as a reference.
        Dim hdc As IntPtr = gr.GetHdc


        ' Make the Metafile, using the reference hDC.
        Dim bounds As New RectangleF(0, 0, Diagram_WidthSize, Diagram_HeightSize)
        Dim mf As New Metafile(filename, hdc, bounds, MetafileFrameUnit.Pixel)

        gr.ReleaseHdc(hdc)

        ' Make a Graphics object and draw.
        gr = Graphics.FromImage(mf)
        gr.PageUnit = GraphicsUnit.Pixel
        gr.Clear(Color.White)

        draw_diagram_background(gr)
        draw_diagram_curve(gr)

        gr.Dispose()
        mf.Dispose()

    End Sub

Private Sub draw_diagram_background(Byval gr as Graphics)

     'some code

End Sub

Private Sub draw_diagram_curve(Byval gr as Graphics)

    'some code

End Sub

End Class

If you use a different filename each time, does that make it work? — Andrew Morton, Jul 09 '20 at 08:34

score 1 · Accepted Answer · answered Oct 30 '20 at 12:58

You need to dispose Diagram_FORM.PictureBox1.Image when you close Form Diagram_FORM, otherwise exception will occur when you init Metafile with same filename c:\temp\test.wmf next time in method create_diagram() of class Diagram:

Dim mf As New Metafile(filename, hdc, bounds, MetafileFrameUnit.Pixel)

You can add the following code in your Diagram_FORM Form to dispose it's PictureBox1.Image when you close it.

Protected Overrides Sub OnFormClosed(e As FormClosedEventArgs)
    If PictureBox1.Image IsNot Nothing Then
        PictureBox1.Image.Dispose()
    End If
    MyBase.OnFormClosed(e)
End Sub

VB.Net Metafile generates error ("A generic error occurred in GDI+")

1 Answers1