Solved

Imagelist shows blank bitmaps

Posted on 2008-10-08
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Last Modified: 2012-05-05
This strikes me as odd - I create a small in-memory bitmap, and draw a single character with a background color on it. I then transfer this into an Imagelist control. However, when I transfer the imagelist.image(x) to a location in a picturebox, only the background color of the image shows up.

I know that the bitmap was created correctly, because if I use "bmp1.save(filename)" then take the file and read it into an image ("dim g as image = image.fromfile(filename)") then load g into the imagelist, it works great.

Can anyone tell me why it doesn't transfer properly to the imagelist unless I save it to disk and read it back?  Thanks!!


Dim bmp1 As New Bitmap(CellWidth, CellHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb)
 

For i = 1 To CellWidth

  For l = 1 To CellHeight

  'draw the '1's' as black

   If Mid$(CellString(i), l, 1) = "1" Then

     bmp1.SetPixel(i - 1, CellHeight - l, Color.Black)

   Else

     bmp1.SetPixel(i - 1, CellHeight - l, Color.DarkGoldenrod)

   End If

  Next l

Next i
 

IList1A.Images.Add(bmp1)

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Comment
Question by:LongDave
  • 4
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8 Comments
 
LVL 55

Expert Comment

by:Jaime Olivares
Comment Utility
try with the following:

yourImgList.ImageSize = new System.Drawing.Size(CellWidth, CellHeight)
yourImgList.Images.Add(bmp1)
yourImgList.TransparentColor = Color.DarkGoldenrod  'optional

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Author Comment

by:LongDave
Comment Utility
Nope - that didn't do it. The wierd thing is that it seems that saving the bmp to a file and then calling it back somehow transforms it so that it loads properly in the Imagelist control. Any other ideas?

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LVL 85

Expert Comment

by:Mike Tomlinson
Comment Utility
Does this make a diff?
        Dim bmp1 As New Bitmap(cellWidth, cellHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb)

        Dim G As Graphics = Graphics.FromImage(bmp1)

        G.Clear(Color.Goldenrod)

        For i = 1 To cellWidth

            For l = 1 To cellHeight

                'draw the '1's' as black

                If Mid$(CellString(i), l, 1) = "1" Then

                    G.FillRectangle(Brushes.Black, New Rectangle(i - 1, cellHeight - l, 1, 1))

                End If

            Next l

        Next i

        G.Dispose()

        IList1A.Images.Add(bmp1)

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Author Comment

by:LongDave
Comment Utility
OK!! That did it! But I still don't see why the use of the bmp directly to the imagelist didn't work properly. Any ideas? I'd really like to understand why. But I will issue you the points - I just didn't want to close the question before your answer.
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LVL 85

Accepted Solution

by:
Mike Tomlinson earned 500 total points
Comment Utility
I really don't have a TECHNICAL answer for you sorry...just haven't really seen anyone using Bitmap.SetPixel() and I knew that my method would work...   =\

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Author Closing Comment

by:LongDave
Comment Utility
Hi, Idle_Mind ... This is the 2nd time you've helped me. Thanks a lot! Your solution looks like it works fine - but I wish I knew WHY the other didn't!  :(
Oh, well!
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LVL 85

Expert Comment

by:Mike Tomlinson
Comment Utility
A simple test using your original technique worked for me...not sure what you did wrong:
Public Class Form1
 

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim CellWidth As Integer = 5

        Dim CellHeight As Integer = 5
 

        Dim pixels As String = "11111,00100,00100,00100,11111;10001,11011,10101,10001,10001"

        For Each charSig As String In pixels.Split(";")

            Dim bmp As New Bitmap(CellWidth, CellHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb)

            Dim rows() As String = charSig.Split(",")

            For y As Integer = 0 To rows.GetUpperBound(0)

                For x As Integer = 0 To rows(y).Length - 1

                    If rows(y).Substring(x, 1) = "1" Then

                        bmp.SetPixel(x, y, Color.Black)

                    Else

                        bmp.SetPixel(x, y, Color.DarkGoldenrod)

                    End If

                Next

            Next

            ImageList1.Images.Add(bmp)

        Next

        PictureBox1.Image = ImageList1.Images(0)

        PictureBox2.Image = ImageList1.Images(1)

    End Sub
 

End Class

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IM-Chars.jpg
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Author Comment

by:LongDave
Comment Utility
Wierd - thanks for the input though. I was using the DrawImage function to place the chars in the picturebox, but I don't know why that would have made any difference (I'm sure it did not).

But thanks again - hope I don't have to bug you too often! :)
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