XtremListBox

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Introduction

Listbox is a control very often used in all applications, mainly for choosing a particular item from a collection of items. However, in the standard ListBox I missed an option to change the color of a selected item, its font and the border color. This article shows how to create your own user control, which will offer a choice of the options described above.

Background

Our new user control will be created on the baseclass of the standard listbox. I called the class which inherits its properties XtremListBox.

Public Class XtremListBox: Inherits System.Windows. Forms. ListBox

Our new class contains all properties of the standard listbox plus my new properties:

• Border color of a selected item
• Font color of a selected item
• Index of the column in which the text to show is saved.
• Font of a selected item
• Length of border color change of a selected item on the x-axis

Our new listbox gets the attribute for re-drawing in two ways:

1. It waits for the SelectedIndexChanged event from the baseclass.

Protected Sub XtremListBox_SelectedIndexChanged(ByVal sender As System.Object, 
    ByVal e As System.EventArgs)  _
Handles MyBase.SelectedIndexChanged
                  _NewDraw()
End Sub

2. It overrides the WndProc function and catches messages sent by Windows to our control.

Protected Overrides Sub WndProc(ByRef msg As System.Windows.Forms.Message)
                  MyBase.WndProc(msg)
                        Select Case msg.Msg
                             Case &H115, &HF, &H360, &H203, &H20A
                             _NewDraw()
                        End Select
End Sub

&H115, &HF, &H360, &H203, &H20A – are message number(WIN API)

You can find the whole list example on this web site: click here.

When we raise an event or a message to redraw ListBox, the core of our new control — the _NewDraw method — is called. This method redraws the standard blue border of the selected item with a new border which will look according to the properties set and it will also add the relevant text.

Public Sub _NewDraw()
    Dim _DrawText As String
    Dim p1, p2 As System.Drawing.PointF
    Dim i As Integer : Dim index As Integer = 0
    Dim str() As DataStruct

    p1.X = 0 : p1.Y = 0 'Starting points of rectangle
    p2.X = mSmoothWidth : p2.Y =
        MyClass.ItemHeight 'Finishing points of rectangle
    'This create smooth brush
    brushStandard = New System.Drawing.Drawing2D.LinearGradientBrush(p1,
        p2, mColor, MyClass.BackColor)

    '1. I get positions of selected items to str(i)._select and I get
    'indexs selected items to str(i)._index
    For i = 0 To MyClass.SelectedIndices.Count - 1
        ReDim Preserve str(i)
        str(i)._select = MyClass.GetItemRectangle(
            MyClass.SelectedIndices.Item(i))
        str(i)._index = MyClass.SelectedIndices.Item(i)
    Next

    If Not IsNothing(str) Then
        For i = 0 To UBound(str)
            '2. I draw rectangle to selected items positions
            MyClass.CreateGraphics.FillRectangle(brushStandard, 0,
                str(i)._select.Y, MyClass.Width, MyClass.ItemHeight)
            '3. I draw text to new rectangles
            If MyClass.Items.Item(0).GetType.Name = "String" Then
                _DrawText = MyClass.Items.Item(str(i)._index)
            Else
                If MyClass.Items.Item(0).item(mTextCol).GetType.Name =
                    "String" Then
                    _DrawText = MyClass.Items.Item(str(i)._index).item(
                        mTextCol)
                Else
                    _DrawText = ""
                End If
            End If
            MyClass.CreateGraphics.DrawString(_DrawText, mFFont,
                mFFontColor, 0, str(i)._select.Y)
        Next
    End If
    brushStandard.dispose()
End Sub

Conclusion

I hope that you find this example useful, especially if you are a beginner coder, to orientate in this issue and to find a way to create your own usercontrols.

History

First release 14.11.2007