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Draw a Line over child control such PictureBox or Group Box using C#

Posted on 2007-11-28
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Last Modified: 2013-12-03
Hi Experts,

How do I draw line over a control ?
Let say like this, I have a Windows Forms, and top of it there are GroupBox and on top of GroupBox there are PictureBox.
And how do I draw a line over GroupBox and PictureBox ?
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Question by:Aryo1
5 Comments
 
LVL 7

Expert Comment

by:bungHoc
ID: 20365004
Try this:

System.Drawing.Pen pen = new System.Drawing.Pen(System.Drawing.Color.Red);
 
System.Drawing.Graphics formGraphics;
formGraphics = this.CreateGraphics();
formGraphics.DrawLine(pen, 50, 50, 100, 100);
pen.Dispose();
formGraphics.Dispose();

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Expert Comment

by:Jaime Olivares
ID: 20366222
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LVL 85

Accepted Solution

by:
Mike Tomlinson earned 500 total points
ID: 20366927
To draw "above" multiple controls, get a DC to the Desktop Window and create a Graphics from that...

In VB.Net:
Public Class Form1
 
    Public Declare Function GetDesktopWindow Lib "user32" () As IntPtr
    Public Declare Function GetWindowDC Lib "user32" (ByVal handle As IntPtr) As IntPtr
    Public Declare Function ReleaseDC Lib "user32" Alias "ReleaseDC" (ByVal handle As IntPtr, ByVal hDc As IntPtr) As Integer
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim desktopHandle As IntPtr = GetDesktopWindow
        Dim desktopDC As IntPtr = GetWindowDC(desktopHandle)
        Dim g As Graphics = Graphics.FromHdc(desktopDC)
 
        Dim ptA As Point = Me.PointToScreen(New Point(0, 0))
        Dim ptB As Point = Me.PointToScreen(New Point(Me.ClientRectangle.Width, Me.ClientRectangle.Height))
        g.DrawLine(Pens.Black, ptA, ptB)
 
        g.Dispose()
        ReleaseDC(desktopDC, desktopHandle)
    End Sub
 
End Class

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Author Comment

by:Aryo1
ID: 20378801
@Idle_Mind

Thx, it seems your solutions can answers my problems.

BTW, Do you have suggestion where should I put this code ?
On Form_Paint or everytime there is change in UI (such as moving some control) ?
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LVL 85

Expert Comment

by:Mike Tomlinson
ID: 20379580
Well...a "catch all" approach would be to use the IMessageFilter() Interface and repaint the line whenever ANY control in your app gets a WM_PAINT message.  If your app is partially obscured though you could end up drawing a line over another apps window since we are drawing with the desktop DC.

Here is an example of IMessageFilter being used:
http://www.experts-exchange.com/Programming/Languages/.NET/Visual_Basic.NET/Q_22696110.html
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