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custom Listbox double buffering

I'm using a custom listbox (which uses System.Windows.Forms.ListBox) and am trying to double buffer it in order to stop the accursed flicker.  My test case uses 4 different items in the list.  In OnDrawItem, I create a new Bitmap of the appropriate size and then create a Graphics from the Bitmap.  Then I "draw" the correct string from the event.  Finally, I draw the Bitmap to the ListBox and then dispose of the graphics objects and bitmap (I've tried without disposing them, with the same results).  Only the first item gets drawn.  Debug.WriteLine code tells me that OnDrawItem is getting called with the appropriate values (text, x & y location, etc.).  As a last ditch effort, I put code into the OnDrawItem that looped through all 4 items, drawing each one.  This resulted in 4 items getting drawn, all with the same, first value (and the expected issues involving improper invalidation... it was just a test, after all).  What have I done wrong?  Who did I wrong in a past life?

protected override void OnDrawItem(DrawItemEventArgs e)
{
base.OnDrawItem(e);
// Verify index is valid before painting
if (e.Index >= 0)
{
for(int i=0;i<4;i++)
{
    Bitmap bmp = GetIndexBitmap(i);//e.Index);
    Graphics graphics = CreateGraphics();
    graphics.DrawImage(bmp, e.Bounds.X, e.Bounds.Y);
    //Debug.WriteLine("index:"+e.Index+"  x="+rectItem.X+"  y="+rectItem.Y);
    graphics.Dispose();
    bmp.Dispose();
  }
}
}


protected Bitmap GetIndexBitmap(int nIndex)
{
Rectangle r = GetItemRectangle(nIndex);
Bitmap offScreenBmp = new Bitmap(r.Width, r.Height);
Graphics offScreenDC = Graphics.FromImage(offScreenBmp);
string sItemText = (string)Items[nIndex];
Debug.WriteLine("index:"+nIndex+"  Items[index]:"+Items[nIndex]+"  str="+sItemText);

pCurrentBrush = m_NormalTextSolidBrush;

// Clear the background for fresh drawing
//offScreenDC.FillRectangle(m_BackSolidBrush, e.Bounds);

// Draw text
{
  offScreenDC.DrawString(sItemText, Font, pCurrentBrush, (float)(r.Left + m_nIndentLeft),(float)(r.Top + m_nIndentTop));
}

Rectangle rectItem = GetItemRectangle(nIndex);
offScreenDC.DrawImage(offScreenBmp, r.X, r.Y);
offScreenDC.Dispose();
return offScreenBmp;
}

}
}
0
rwinkler
Asked:
rwinkler
  • 2
2 Solutions
 
rama_krishna580Commented:
0
 
ptmcompCommented:
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Runtime.InteropServices;

namespace TestDoubleBuffer
{
      public class DoubleBufferListView: ListView
      {
            public const int WM_PAINT = 0x000F;
            public const int WM_PRINT = 0x0317;
            public const int WM_PRINTCLIENT = 0x0318;
            public const int WM_ERASEBKGND = 0x0014;

            public const int PRF_CHECKVISIBLE = 0x00000001;
            public const int PRF_NONCLIENT    = 0x00000002;
            public const int PRF_CLIENT       = 0x00000004;
            public const int PRF_ERASEBKGND   = 0x00000008;
            public const int PRF_CHILDREN     = 0x00000010;
            public const int PRF_OWNED        = 0x00000020;

            [DllImport("User32.DLL")]
            public static extern int SendMessage(          
                  IntPtr hWnd,
                  uint Msg,
                  IntPtr wParam,
                  IntPtr lParam
                  );

            public DoubleBufferListView(): base()
            {
                  SetStyle(ControlStyles.DoubleBuffer, false);
                  SetStyle(ControlStyles.Opaque, true);
                  //SetStyle(ControlStyles.UserPaint, true);
            }

            private Bitmap bufferBmp = null;
            protected Bitmap GetBitmap(Graphics g)
            {
                  if ((bufferBmp == null) || (bufferBmp.Size != ClientRectangle.Size))
                  {
                        bufferBmp = new Bitmap(ClientRectangle.Width, ClientRectangle.Height, g);
                  }
                  return bufferBmp;
            }

            protected override void WndProc(ref Message m)
            {
                  switch (m.Msg)
                  {
                        case WM_PAINT:
                              using(Graphics gWin = Graphics.FromHwnd(m.HWnd))
                              {
                                    Bitmap bmp = GetBitmap(gWin);
                                    using (Graphics gBmp = Graphics.FromImage(bmp))
                                    {
                                          IntPtr hDc;
                                          gBmp.FillRectangle(SystemBrushes.Window, 0, 0, bmp.Width, bmp.Height);
                                          hDc = gBmp.GetHdc();

                                          m.WParam = hDc;
                                          base.WndProc(ref m);
                                          m.WParam = IntPtr.Zero;
                                          //InvokePaint(this, new PaintEventArgs(gBmp, ClientRectangle));
                                          //OnPaint(new PaintEventArgs(gBmp, ClientRectangle));
                                          //Message printMessage = Message.Create(m.HWnd, WM_PRINTCLIENT, gBmp.GetHdc(), new IntPtr(PRF_CLIENT | PRF_ERASEBKGND));
                                          //SendMessage(m.HWnd, WM_PRINTCLIENT, hDc, new IntPtr(PRF_CLIENT | PRF_ERASEBKGND));
                                          gBmp.ReleaseHdc(hDc);
                                          //gBmp.FillRectangle(SystemBrushes.Desktop, 0, 0, bmp.Width, bmp.Height);
                                    }
                                    gWin.DrawImageUnscaled(bmp, 0, 0, bmp.Width, bmp.Height);
                              }
                              m.Result = IntPtr.Zero;
                              break;
                        case WM_ERASEBKGND :
                              m.Result = new IntPtr(1);
                              break;
                        default:
                              base.WndProc(ref m);
                              break;
                  }
            }
      }
}
0
 
ptmcompCommented:
Oops the commented lines are not necessary... ;o)
0

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