VB.NET ComboBox.DrawItem事件代码示例

Friend WithEvents ComboBox1 As System.Windows.Forms.ComboBox
  Private animals() As String

  ' This method initializes the owner-drawn combo box.
  ' The drop-down width is set much wider than the size of the combo box
  ' to accomodate the large items in the list.  The drop-down style is set to 
  ' ComboBox.DropDown, which requires the user to click on the arrow to 
  ' see the list.
  Private Sub InitializeComboBox()
      Me.ComboBox1 = New ComboBox
      Me.ComboBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawVariable
      Me.ComboBox1.Location = New System.Drawing.Point(10, 20)
      Me.ComboBox1.Name = "ComboBox1"
      Me.ComboBox1.Size = New System.Drawing.Size(100, 120)
      Me.ComboBox1.DropDownWidth = 250
      Me.ComboBox1.TabIndex = 0
      Me.ComboBox1.DropDownStyle = ComboBoxStyle.DropDown
      animals = New String() {"Elephant", "c r o c o d i l e", "lion"}
      ComboBox1.DataSource = animals
      Me.Controls.Add(Me.ComboBox1)
  End Sub

  ' If you set the Draw property to DrawMode.OwnerDrawVariable, 
  ' you must handle the MeasureItem event. This event handler 
  ' will set the height and width of each item before it is drawn. 
   Private Sub ComboBox1_MeasureItem(ByVal sender As Object, _
      ByVal e As System.Windows.Forms.MeasureItemEventArgs) _
          Handles ComboBox1.MeasureItem

      Select Case e.Index
          Case 0
              e.ItemHeight = 45
          Case 1
              e.ItemHeight = 20
          Case 2
              e.ItemHeight = 35
      End Select
      e.ItemWidth = 260

  End Sub

  ' You must handle the DrawItem event for owner-drawn combo boxes.  
  ' This event handler changes the color, size and font of an 
  ' item based on its position in the array.
  Private Sub ComboBox1_DrawItem(ByVal sender As Object,  _ 
      ByVal e As System.Windows.Forms.DrawItemEventArgs) _
      Handles ComboBox1.DrawItem

      Dim size As Single
      Dim myFont As System.Drawing.Font
      Dim family As FontFamily

      Dim animalColor As New System.Drawing.Color
      Select Case e.Index
          Case 0
              size = 30
              animalColor = System.Drawing.Color.Gray
              family = FontFamily.GenericSansSerif
          Case 1
              size = 10
              animalColor = System.Drawing.Color.LawnGreen
              family = FontFamily.GenericMonospace
          Case 2
              size = 15
              animalColor = System.Drawing.Color.Tan
              family = FontFamily.GenericSansSerif
      End Select

      ' Draw the background of the item.
      e.DrawBackground()

      ' Create a square filled with the animals color. Vary the size
      ' of the rectangle based on the length of the animals name.
      Dim rectangle As Rectangle = New Rectangle(2, e.Bounds.Top + 2, _
          e.Bounds.Height, e.Bounds.Height - 4)
      e.Graphics.FillRectangle(New SolidBrush(animalColor), rectangle)

      ' Draw each string in the array, using a different size, color,
      ' and font for each item.
      myFont = New Font(family, size, FontStyle.Bold)
      e.Graphics.DrawString(animals(e.Index), myFont, System.Drawing.Brushes.Black, _
          New RectangleF(e.Bounds.X + rectangle.Width, e.Bounds.Y, _ 
          e.Bounds.Width, e.Bounds.Height))

      ' Draw the focus rectangle if the mouse hovers over an item.
      e.DrawFocusRectangle()
  End Sub

' 导入命名空间
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Drawing.Drawing2D

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.XButton = New System.Windows.Forms.Button
        Me.ColorList = New System.Windows.Forms.ComboBox
        Me.SuspendLayout()
        '
        'XButton
        '
        Me.XButton.Location = New System.Drawing.Point(112, 24)
        Me.XButton.Name = "XButton"
        Me.XButton.Size = New System.Drawing.Size(75, 23)
        Me.XButton.TabIndex = 0
        Me.XButton.Text = "Button1"
        Me.XButton.UseVisualStyleBackColor = True
        '
        'ColorList
        '
        Me.ColorList.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed
        Me.ColorList.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList
        Me.ColorList.FormattingEnabled = True
        Me.ColorList.Location = New System.Drawing.Point(88, 64)
        Me.ColorList.Name = "ColorList"
        Me.ColorList.Size = New System.Drawing.Size(121, 21)
        Me.ColorList.TabIndex = 1
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(292, 221)
        Me.Controls.Add(Me.ColorList)
        Me.Controls.Add(Me.XButton)
        Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle
        Me.MaximizeBox = False
        Me.Name = "Form1"
        Me.Text = "Control Drawing"
        Me.ResumeLayout(False)

    End Sub
    Friend WithEvents XButton As System.Windows.Forms.Button
    Friend WithEvents ColorList As System.Windows.Forms.ComboBox

End Class
Public Class Form1
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        ColorList.Items.Add("Red")
        ColorList.Items.Add("Orange")
        ColorList.Items.Add("Yellow")
        ColorList.Items.Add("Green")
        ColorList.Items.Add("Blue")
        ColorList.Items.Add("Indigo")
        ColorList.Items.Add("Violet")
    End Sub

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        e.Graphics.DrawEllipse(Pens.Black, 10, 10, Me.ClientRectangle.Width - 20, _
            Me.ClientRectangle.Height - 20)
    End Sub

    Private Sub XButton_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles XButton.Paint
        Dim usePen As Pen

        e.Graphics.Clear(SystemColors.Control)

        usePen = New Pen(SystemColors.ControlText, 3)
        e.Graphics.DrawRectangle(usePen, XButton.ClientRectangle)

        usePen.Dispose()
    End Sub

    Private Sub ColorList_DrawItem(ByVal sender As Object, ByVal e As System.Windows.Forms.DrawItemEventArgs) Handles ColorList.DrawItem
        Dim useBrush As Brush

        If (e.Index = -1) Then Return

        e.DrawBackground()

        useBrush = New SolidBrush(Color.FromName(CStr(ColorList.Items(e.Index))))
        e.Graphics.FillRectangle(useBrush, _
            e.Bounds.Left + 2, e.Bounds.Top + 2, _
            e.Bounds.Width - 4, e.Bounds.Height - 4)
        useBrush.Dispose()

        e.Graphics.DrawRectangle(Pens.Black, _
            e.Bounds.Left + 2, e.Bounds.Top + 2, _
            e.Bounds.Width - 4, e.Bounds.Height - 4)
        e.DrawFocusRectangle()
    End Sub

    Private Sub XButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles XButton.Click
        MsgBox("Button clicked.")
    End Sub
End Class

public class ComboBoxCellRenderer
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class