Drawing on[/underneath!] Controls

Drawing on[/underneath!] Controls

• Robs Pierre

  So why does my line control cover the listbox

  class Line : Control
  {
   Pen _Pen;
  
   Line()
   {
     this.SetStyle(ControlStyles.SupportsTransparentBackColor, true);
     this.BackColor = Color.Transparent; 
   }
  
   public void SetBounds(int Width)
   {
     _Pen = new Pen(new SolidBrush(Color.Red));
     _Pen.Width = Width;
     this.Location = new Point(0, 0);
     this.Height = Form1.ClientRectangle.Height;
     this.Width = Form1.ClientRectangle.Width;
     Invalidate();
   }
  
   protected override void OnPaint(System.Windows.Forms.PaintEventArgs e)
   {
     base.OnPaint(e);
     _Pen.DashCap = DashCap.Flat;
     _Pen.DashStyle = DashStyle.DashDotDot;
     _Pen.StartCap = LineCap.Flat;
     _Pen.EndCap = LineCap.ArrowAnchor;
     Graphics g = this.CreateGraphics;
     g.DrawBezier(_Pen, 20, 20, 500, 300, 550, 320, 510, 60);
   }
  }

  
  

• hemo

  Try this instead:
  
  using System;
  using System.Drawing;
  using System.Windows.Forms;
  
  public class Line : Control {
  protected override CreateParams CreateParams {
  get {
  // Turn on the WS_EX_TRANSPARENT style
  CreateParams cp = base.CreateParams;
  cp.ExStyle |= 0x20;
  return cp;
  }
  }
  protected override void OnPaintBackground(PaintEventArgs pevent) {
  // Do *not* paint the background
  }
  protected override void OnPaint(PaintEventArgs e) {
  // Draw the line, just a demo here:
  e.Graphics.DrawLine(Pens.Black, 0, 0, this.Width, this.Height);
  base.OnPaint(e);
  }
  }
  
  If you animate the line in any way, you'll need to invalidate the control's Parent so the background is redrawn correctly.
  
  
  

• Jafar Bhatti

  Thats a really working one thanks. BTW, could you please explain what it does in the CreateParams
  

• Nodnarb501

  Can we then create the line as a control and set its background to transparent so the list box is visible through
  

• Neil Ault

  Yes, that would work. Very similar to what you did with the transparent form.
  
  
  

• Jesper Ekenberg

  Because this.BackColor = Color.Transparent; doesn't realy work as expected.
  

• David Hanak

  As indicated, it turns on the WS_EX_TRANSPARENT window style. With this style set, Windows ensures that all windows "below" the window get painted first and the transparent window last.
  
  
  

• Robert G Lewis

  So any alternatives
  

• Jayakumar A

  No. You've got two distinct windows here. One for the form, another for the control. You can't draw on both.
  
  
  
• Drawing on[/underneath!] Controls