Adding a standard border to a control

The Control class doesn't have a border style property so creating controls with standard borders can present a problem. Many people assume the border is drawn in the OnPaint override but this creates a problem because it uses up some of the client rectangle which always has to be compensated for when doing the "real" drawing in a control. Really, the control border should be a non-client item and drawn for us by the system. The secret to enabling this feature is in the window creation parameters which are used every time a control is created or recreated.

The CreateParams property may be overridden to return a set of creation parameters that include the flags which add borders to the control. There also needs to be a mechanism for specifying which border is to be displayed so a property of type BorderStyle is ideal.

The basic control shown in the following C# and VB listings show how to do this.

Imports System

Imports System.ComponentModel

Imports System.Windows.Forms

Namespace controlborders

Public Class ControlEx

Inherits Control

Private _borderStyle As BorderStyle

< _

Category("Appearance"), _

Description("The border style") _

> _

Public Property BorderStyle() As BorderStyle

Get

Return _borderStyle

End Get

Set(ByVal Value As BorderStyle)

_borderStyle = Value

Me.RecreateHandle()

Invalidate()

End Set

End Property

Protected Overrides ReadOnly Property CreateParams() As CreateParams

Get

Const WS_BORDER As Integer = &H800000

Const WS_EX_STATICEDGE As Integer = &H20000

Dim cp As CreateParams = MyBase.CreateParams

Select Case _borderStyle

Case BorderStyle.FixedSingle

cp.Style = cp.Style Or WS_BORDER

Case BorderStyle.Fixed3D

cp.ExStyle = cp.ExStyle Or WS_EX_STATICEDGE

End Select

Return cp

End Get

End Property

Public Sub New()

End Sub 'New

End Class 'ControlEx

End Namespace 'controlborders

namespace controlborders

{

using System;

using System.Windows.Forms;

public class ControlEx : Control

{

private BorderStyle _borderStyle;

[

Category("Appearance"),

Description("The border style")

]

public BorderStyle BorderStyle

{

get

{

return _borderStyle;

}

set

{

_borderStyle = value;

this.RecreateHandle();

Invalidate();

}

protected override CreateParams CreateParams

{

get

{

const int WS_BORDER=0x00800000;

const int WS_EX_STATICEDGE=0x00020000;

CreateParams cp=base.CreateParams;

switch (_borderStyle)

{

case BorderStyle.FixedSingle:

cp.Style|=WS_BORDER;

break;

case BorderStyle.Fixed3D:

cp.ExStyle |= WS_EX_STATICEDGE;

break;

}

return cp;

}

public ControlEx()

{

}

Any class which derives from ControlEx will now have a BorderStyle property that can be used to select the FixedSingle or Fixed3D styles.

Return to the Tips and Tricks index