Paint Events

[Barguast]

I touched on this in my last topic. I've been unable to get a 'Paint' event for a TextBox working - this is documented in the .NET help, but it is not listed in the Events list of the control (In VC#). I tried to write one into the code myself but it never triggers.

// In InitializeComponent ()
this.txtText.Paint += new System.Windows.Forms.PaintEventHandler(this.txtText_Paint);
// Paint function
private void txtText_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
     // This function never runs
}

Am I doing something wrong? I also notice that the TreeView control doesn't have a Paint event at all - is there a suitable alternative I can use?

[raysoft_jack]

You can use gdi32 instead.

using System.Runtime.InteropServices;
using System.Drawing;

public class API {
    [DllImport("user32.dll", EntryPoint="GetWindowDC")]
    public static extern int GetWindowDC (
        int hwnd
    );

    [DllImport("user32.dll", EntryPoint="ReleaseDC")]
    public static extern int ReleaseDC (
        int hwnd,
        int hdc
    );
}


public class Form1 : System.Windows.Forms.Form {

    private TreeView       TV;

    //
    // IDE generated codes ............
    //

    private void DrawOnTheControl( ref Control c ) {

        int hWnd= c.Handle.ToInt32();
        int hDC = API.GetWindowDC( hWnd );

        Graphics canvas = Graphics.FromHdc( new IntPtr( hDC ) );
        // Do some drawings;

        // Don't forget to release the gdi object
        API.REleaseDC( hWnd , hDC );
    }

}

[Barguast]

Surely I need an event to call the DrawOnTheControl function? And since the function performs drawing it'd be a Paint event (which the TextBox and Tree controls don't seem to have)

... Unless I'm missing something

[raysoft_jack]

A Paint event of a control is raised when there is something changed on the control or it's surrounding.

So add DrawOnTheControl( ref treeviewInstance ) to the following events' handlers :

SizeChanged , Resize , DrawItem ( if exist ) , SelectedItemChanged , etc.

[Barguast]

Ah, I see. Just out of curiousity, but why don't these controls have Paint events?

[Pirate]

Originally posted by raysoft_jack
You can use gdi32 instead.

using System.Runtime.InteropServices;
using System.Drawing;

public class API {
    [DllImport("user32.dll", EntryPoint="GetWindowDC")]
    public static extern int GetWindowDC (
        int hwnd
    );

    [DllImport("user32.dll", EntryPoint="ReleaseDC")]
    public static extern int ReleaseDC (
        int hwnd,
        int hdc
    );
}


public class Form1 : System.Windows.Forms.Form {

    private TreeView       TV;

    //
    // IDE generated codes ............
    //

    private void DrawOnTheControl( ref Control c ) {

        int hWnd= c.Handle.ToInt32();
        int hDC = API.GetWindowDC( hWnd );

        Graphics canvas = Graphics.FromHdc( new IntPtr( hDC ) );
        // Do some drawings;

        // Don't forget to release the gdi object
        API.REleaseDC( hWnd , hDC );
    }

}

I wouldn't use this unmanaged code . You can get same functionality in managed GDI+ .Just a thought ...

[raysoft_jack]

Well, I see ... ... I forget it has a CreateGraphics() method.

public class Form1 : System.Windows.Forms.Form {

    private TreeView       TV;

    //
    // IDE generated codes ............
    //

    private void DrawOnTheControl( ref Control c ) {
        Graphics canvas = c.CreateGraphics();

        // Call some mathods of canvas;

        canvas.Flush();
        canvas.Dispose();
    }

}

[Barguast]

Urgh... I still can't get this right. I tried the suggested events for calling the DrawOnTheControl function, but it still won't paint it when the control first appears. I tried instead to draw the borders when the form is initialised or resize, for example:

private void frmMain_Load(object sender, System.EventArgs e)
{
     drawBorder (textBox1, Color.Blue);
}

private void drawBorder (Control ctrl, Color colour)
{
     Graphics g = ctrl.CreateGraphics ();
     Pen p = new Pen (colour, 2);
	
     g.DrawRectangle (p,
          ctrl.ClientRectangle.Left, ctrl.ClientRectangle.Top,
          ctrl.ClientRectangle.Width, ctrl.ClientSize.Height);
            	
     g.Flush ();
     g.Dispose ();
}

It works ok with the resize event (although you can still see 'trails' of the original black colour), but the Load function doesn't work at all - I'm guessing this is because the control hasn't been loaded yet.

Is there not a better way to do this?

Also, while I've got the code posted, how can I pass the control in by reference? I've tried using 'ref' but it complains about me passing a TextBox rather a Control.

Thanks with your help so far, though