ListBox.OnDrawItem(DrawItemEventArgs) 方法

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

引发 DrawItem 事件。

protected:
 virtual void OnDrawItem(System::Windows::Forms::DrawItemEventArgs ^ e);

protected virtual void OnDrawItem (System.Windows.Forms.DrawItemEventArgs e);

abstract member OnDrawItem : System.Windows.Forms.DrawItemEventArgs -> unit
override this.OnDrawItem : System.Windows.Forms.DrawItemEventArgs -> unit

Protected Overridable Sub OnDrawItem (e As DrawItemEventArgs)

参数

e

DrawItemEventArgs

包含事件数据的 DrawItemEventArgs。

示例

下面的代码示例演示如何创建所有者绘制 ListBox 的项。 代码使用 DrawMode 属性指定绘制的项大小固定，以及 DrawItem 执行将每个项绘制到 中的 ListBox事件。 示例代码使用作为参数传递给事件处理程序的 DrawItemEventArgs 类的属性和方法来绘制项。 此示例要求 ListBox 已将名为 的 listBox1 控件添加到窗体中， DrawItem 并且该事件由示例代码中定义的事件处理程序处理。 该示例还要求已按该顺序将 ListBox 文本为“Apple”、“Orange”和“Plum”的项添加到 。

private ListBox ListBox1 = new ListBox();
private void InitializeListBox()
{
    ListBox1.Items.AddRange(new Object[] 
        { "Red Item", "Orange Item", "Purple Item" });
    ListBox1.Location = new System.Drawing.Point(81, 69);
    ListBox1.Size = new System.Drawing.Size(120, 95);
    ListBox1.DrawMode = DrawMode.OwnerDrawFixed;
    ListBox1.DrawItem += new DrawItemEventHandler(ListBox1_DrawItem);
    Controls.Add(ListBox1);
}

private void ListBox1_DrawItem(object sender, 
    System.Windows.Forms.DrawItemEventArgs e)
{
    // Draw the background of the ListBox control for each item.
    e.DrawBackground();
    // Define the default color of the brush as black.
    Brush myBrush = Brushes.Black;

    // Determine the color of the brush to draw each item based 
    // on the index of the item to draw.
    switch (e.Index)
    {
        case 0:
            myBrush = Brushes.Red;
            break;
        case 1:
            myBrush = Brushes.Orange;
            break;
        case 2:
            myBrush = Brushes.Purple;
            break;
    }

    // Draw the current item text based on the current Font 
    // and the custom brush settings.
    e.Graphics.DrawString(ListBox1.Items[e.Index].ToString(), 
        e.Font, myBrush, e.Bounds, StringFormat.GenericDefault);
    // If the ListBox has focus, draw a focus rectangle around the selected item.
    e.DrawFocusRectangle();
}

Private WithEvents ListBox1 As New ListBox()

Private Sub InitializeListBox() 
    ListBox1.Items.AddRange(New Object() _
        {"Red Item", "Orange Item", "Purple Item"})
    ListBox1.Location = New System.Drawing.Point(81, 69)
    ListBox1.Size = New System.Drawing.Size(120, 95)
    ListBox1.DrawMode = DrawMode.OwnerDrawFixed
    Controls.Add(ListBox1)

End Sub

Private Sub ListBox1_DrawItem(ByVal sender As Object, _
 ByVal e As System.Windows.Forms.DrawItemEventArgs) _
 Handles ListBox1.DrawItem

    ' Draw the background of the ListBox control for each item.
    e.DrawBackground()

    ' Define the default color of the brush as black.
    Dim myBrush As Brush = Brushes.Black

    ' Determine the color of the brush to draw each item based on   
    ' the index of the item to draw.
    Select Case e.Index
        Case 0
            myBrush = Brushes.Red
        Case 1
            myBrush = Brushes.Orange
        Case 2
            myBrush = Brushes.Purple
    End Select

    ' Draw the current item text based on the current 
    ' Font and the custom brush settings.
    e.Graphics.DrawString(ListBox1.Items(e.Index).ToString(), _
        e.Font, myBrush, e.Bounds, StringFormat.GenericDefault)

    ' If the ListBox has focus, draw a focus rectangle around  _ 
    ' the selected item.
    e.DrawFocusRectangle()
End Sub

注解

引发事件时，将通过委托调用事件处理程序。 有关详细信息，请参阅 处理和引发事件。

方法 OnDrawItem 还使派生类无需附加委托即可处理 事件。 这是在派生类中处理事件的首选技术。

继承者说明

在派生类中重写 OnDrawItem(DrawItemEventArgs) 时，一定要调用基类的 OnDrawItem(DrawItemEventArgs) 方法，以便已注册的委托对事件进行接收。

另请参阅

• DrawItem