Generating Missing Paint Event for TreeView and ListView Controls

• Download source and demo project - 16 KB

Introduction

Microsoft .NET forms controls like TreeView and Listview are just wrappers around the controls in ComCtl. As such, they do not normally invoke the Paint event. The only suggestion I have seen posted is to set the ControlStyles.UserPaint style and do all the drawing yourself!

TreeViewWithPaint Control

To solve this problem, an internal Graphics object based on a Bitmap was used. It is re-created during any Resize.

//Recreate internal graphics object
protected override void OnResize( System.EventArgs e ) {
    if( internalBitmap == null  ||
        internalBitmap.Width != Width || internalBitmap.Height != Height ) {

        if( Width != 0 && Height != 0 ) {
            DisposeInternal();
            internalBitmap = new Bitmap( Width, Height );
            internalGraphics = Graphics.FromImage( internalBitmap );
        }
    }
}

When the control receives a WM_PAINT, three steps are performed:

1. The ComCtl is painted into the internal Graphics object via a WM_PRINTCLIENT message.

   //Draw Internal Graphics
   IntPtr hdc = internalGraphics.GetHdc();
   Message printClientMessage = Message.Create( Handle, 
        WM_PRINTCLIENT, hdc, IntPtr.Zero );  
   DefWndProc( ref printClientMessage );
   internalGraphics.ReleaseHdc( hdc );

2. The OnPaint() is now invoked using PaintEventArgs constructed from the internal Graphics object.

   //Add the missing OnPaint() call
   OnPaint( new PaintEventArgs( internalGraphics, Rectangle.FromLTRB( 
       updateRect.left,
       updateRect.top,
       updateRect.right,
       updateRect.bottom ) ) );

3. The Bitmap of the internal Graphics object is copied to the normal screen Graphics device.

   //Draw Screen Graphics
   screenGraphics.DrawImage( internalBitmap, 0, 0 );

Also, the WM_ERASEBKGND was filtered out to remove flicker.

case WM_ERASEBKGND:
    //removes flicker
    return;

Also, the Paint event was added to restore browsable attributes.

[
//Re-enable Attributes for the Paint Event
EditorBrowsableAttribute( EditorBrowsableState.Always ),
BrowsableAttribute(true)
]
public new event PaintEventHandler Paint {
    add   { base.Paint += value; }
    remove{ base.Paint -= value; }
}

Using the Code

To use the TreeViewWithPaint control:

1. Just add the control to the toolbox.
2. Drag it on to your form.
3. Attach a Paint handler to the now exposed Paint event.

To create a <AnotherComCtl>WithPaint, modify TreeViewWithPaint as follows:

1. Use <AnotherComCtl> as the base class.
2. Copy the <AnotherComCtl> class attributes to the <AnotherComCtl>WithPaint class.
3. Add an <AnotherComCtl>WithPaint.bmp, which is a 16x16 bit map used for the toolbox icon.

TreeViewWithPaint Control Test Bench

I created a simple Form containing a single TreeViewWithPaint control. The Paint event can now be used.

treeViewWithPaint1.Paint += new PaintEventHandler( 
       treeViewWithPaint1_Paint );

This particular Paint handler just draws a simple white band inside the selected node.

//Add a simple yellow band inside the selected node
private void treeViewWithPaint1_Paint(object sender, PaintEventArgs e) {
    Graphics g = e.Graphics;
    TreeNode node = treeViewWithPaint1.SelectedNode;
    
    if( node != null && node.IsVisible ) {
        using( Pen pen = new Pen( Color.Yellow ) ) {
            g.DrawRectangle( pen, 
                node.Bounds.X + 1,
                node.Bounds.Y + 1,
                node.Bounds.Width  - 3,
                node.Bounds.Height - 3
                );
        }
    }
}

Points of Interest

• The needed attributes were discovered by using the VB (not C#) object browser for VS 2002 (not VS 2003).
• There is an undocumented feature of XP that horizontal scroll bars appear on TreeView if you add items at design time.

License

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