Class for drawing a flat color border

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• Download demo project - 16.7 KB

Introduction

Standard Windows Forms controls don't allow you to change border colors. I introduce here the BorderDrawer class which contains a simple code that helps to solve this problem. You may use this class for creating your custom controls.

BorderDrawer Class

1. Private fields:
C#

private Color borderColor = Color.Black;   // default border color is black
private static int WM_NCPAINT = 0x0085;    // WM_NCPAINT message
private static int WM_ERASEBKGND = 0x0014; // WM_ERASEBKGND message
private static int WM_PAINT = 0x000F;      // WM_PAINT message

2. The DrawBorder(ref Message message, int width, int height) method:
C#

// message - a message from control's WndProc(ref Message m) method
// width - controls' width
// height - controls' height
public void DrawBorder(ref Message message, int width, int height)
{
     if (message.Msg == WM_NCPAINT || message.Msg == WM_ERASEBKGND || 
         message.Msg == WM_PAINT)
     {
          //get handle to a display device context
          IntPtr hdc = GetDCEx(message.HWnd, (IntPtr)1, 1 | 0x0020);
         
          if (hdc != IntPtr.Zero)
          {
              //get Graphics object from the display device context
              Graphics graphics = Graphics.FromHdc(hdc);
              Rectangle rectangle = new Rectangle(0, 0, width, height);
              ControlPaint.DrawBorder(graphics, rectangle, 
                           borderColor, ButtonBorderStyle.Solid);

              message.Result = (IntPtr)1;
              ReleaseDC(message.HWnd, hdc);
          }           
     }
}

3. The BorderColor property:
C#

public Color BorderColor
{
    get { return borderColor; }
    set { borderColor = value; }
}

4. Here are the imported functions:
C#

//The GetDCEx function retrieves a handle to a display device context
//(DC) for the client area of a specified window
[DllImport("user32.dll")]
static extern IntPtr GetDCEx(IntPtr hwnd, IntPtr hrgnclip, uint fdwOptions);
//the ReleaseDC function releases a device context (DC)
[DllImport("user32.dll")]
static extern int ReleaseDC(IntPtr hwnd, IntPtr hDC);

Using the code

To get results, you only need to do four things:

1. Include in your control class, the BorderDrawer's object:
C#

private BorderDrawer borderDrawer = new BorderDrawer();

2. Override the WndProc(ref Message m) method.
3. Call the DrawBorder(...) method in the overridden WndProc(ref Message m) method.

Note that calling DrawBorder(...) should be after(!) calling base.WndProc(ref m).

C#

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    borderDrawer.DrawBorder(ref m, this.Width, this.Height);
}

4. Add a property that allows to change the border color.
C#

public Color BorderColor
{
    get { return borderDrawer.BorderColor; }
    set
    {
        borderDrawer.BorderColor = value;
        Invalidate();
    }
}

Example

Let's repaint the TextBox border using BorderDrawer:

public class TextBoxWithColorBorder : TextBox
{
    //creating instance of BorderDrawer class
    private BorderDrawer borderDrawer = new BorderDrawer();

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        //calling DrawBorder method
        borderDrawer.DrawBorder(ref m, this.Width, this.Height);
    }

    //this property allows control's users change border color
    public Color BorderColor
    {
        get { return borderDrawer.BorderColor; }
        set
        {
            borderDrawer.BorderColor = value;
            Invalidate();
        }
    }
}

Happy coding!