On the previous page, this article showed how to create a custom control using VB.NET and inheritance.
Because our new control is not in our toolbox, we have to create it on the form with code. The best place to do this is in the form Load event procedure. Here's how to code that:
Open the code window for the form load event procedure and add this code:
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
Dim MyCheckBox As New newCheckBox()
With MyCheckBox
.Text = "Custom Colored Check Box"
.Left = oldCheckBox.Left
.Top = oldCheckBox.Top + OldCheckBox.Height
.Size = oldCheckBox.Size
End With
Controls.Add(MyCheckBox)
End Sub
To place the new checkbox on the form, we've taken advantage of the fact that there is already one one there and just used the size and position of that one. Otherwise we would have to code the position manually. When MyCheckBox has been added to the form, we then add it to the Controls collection.
But there are several problems with this code.
- It doesn't work unless the default position of the Checkbox (RightToLeft = No) is used. The hardcoded "Dim CenterSquare As New Rectangle(2, 3, 9, 9)" causes this problem.
- The color Red is hardcoded and changing the color requires changing the program.
Here's a new, improved CheckBox class. I won't explain this one completely, but it shows you how to take one of the next steps toward VB.NET object oriented coding.
Public Class betterCheckBox
Inherits CheckBox
'
'Syntax:
'
' object.FillImage = New Bitmap(Filename:="filename")
' object.FillColor = Color.colorname
' The Bitmap object file can be of several different
' formats and any size.
' It's recommended that you have an image close to 9x9
' pixels because GDI+ will resize the image to that size
' automatically and this can produce horrendous results.
' If the FillImage property is not provided, the FillColor
' will be used to fill the box.
' If the FillColor property is also missing,
' a standard checkmark is displayed.
'
Private CenterSquareColor As Color
Private CenterSquareImage As Bitmap
Protected Overrides Sub OnPaint _
(ByVal pEvent As System.Windows.Forms.PaintEventArgs)
' Allow for any size checkbox to be properly filled
' The IIF Statement determines which side of the
' CheckBox object the box is actually on.
' The (Me.Height / 2) - 4 finds the top of the area
' to be filled in
' The 9, 9 is the height and width of the
' interior of the CheckBox box.
Dim CenterSquare As New Rectangle( _
IIf(Me.RightToLeft = RightToLeft.No, _
2, Me.Width - 12), (Me.Height / 2) - 5, 9, 9)
MyBase.OnPaint(pEvent)
If Me.Checked Then
' Fill in the box with the predetermined
' Color() (using a solid brush)
If CenterSquareImage Is Nothing Then
pEvent.Graphics.FillRectangle( _
New SolidBrush( _
CenterSquareColor), CenterSquare)
Else
' Fill in the box with the an the
' image that was passed
pEvent.Graphics.DrawImage( _
CenterSquareImage, CenterSquare)
End If
End If
End Sub
Public Property FillColor() As Color
Get
FillColor = CenterSquareColor
End Get
Set(ByVal Value As Color)
CenterSquareColor = Value
End Set
End Property
Public Property FillImage() As Bitmap
Get
FillImage = CenterSquareImage
End Get
Set(ByVal Value As Bitmap)
CenterSquareImage = Value
End Set
End Property
End Class
On the next page, some of the features of the new, improved code are explained.
