ListBox.OnDrawItem(DrawItemEventArgs) 方法

定义

引发 DrawItem 事件。Raises the DrawItem event.

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 DrawItemEventArgsA DrawItemEventArgs that contains the event data.

示例

下面的代码示例演示如何创建所有者描述的 ListBox 项。The following code example demonstrates how to create owner-drawn ListBox items. 此代码使用 DrawMode 属性来指定所绘制的项固定大小,并使用 DrawItem 事件来执行每个项到 ListBox的绘制。The code uses the DrawMode property to specify that the items drawn are fixed sized and the DrawItem event to perform the drawing of each item into the ListBox. 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。The example code uses the properties and methods of the DrawItemEventArgs class passed as a parameter to the event handler to draw the items. 此示例要求将 listBox1 ListBox 控件添加到窗体中,并且 DrawItem 事件由示例代码中定义的事件处理程序进行处理。This example requires that a ListBox control called listBox1 has been added to a form and that the DrawItem event is handled by the event handler defined in the example code. 该示例还要求使用文本 "Apple"、"橙色" 和 "Plum" 将项添加到 ListBox 中。The example also requires that items have been added to the ListBox with the text of "Apple", "Orange", and "Plum" in that order.

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。Raising an event invokes the event handler through a delegate. 有关详细信息,请参阅处理和引发事件For more information, see Handling and Raising Events.

利用 OnDrawItem 方法,派生类还可以处理事件,而无需附加委托。The OnDrawItem method also enables derived classes to handle the event without attaching a delegate. 这是在派生类中处理事件的首选技术。This is the preferred technique for handling the event in a derived class.

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。When overriding OnDrawItem(DrawItemEventArgs) in a derived class, be sure to call the base class's OnDrawItem(DrawItemEventArgs) method so that registered delegates receive the event.

适用于

另请参阅