ListBox.DrawItem 事件

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

在所有者绘制的 ListBox 的可视方位更改时发生。

public:
 event System::Windows::Forms::DrawItemEventHandler ^ DrawItem;

public event System.Windows.Forms.DrawItemEventHandler? DrawItem;

member this.DrawItem : System.Windows.Forms.DrawItemEventHandler 

Public Custom Event DrawItem As DrawItemEventHandler 

事件类型

DrawItemEventHandler

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，并使用 DrawItem 事件将每个项绘制到 中 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。 此示例要求已将名为 的ListBoxlistBox1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 中。

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

此事件由所有者绘制 ListBox的 使用。 仅当 属性设置为 DrawMode.OwnerDrawFixed 或 DrawMode.OwnerDrawVariable时，DrawMode才会引发 事件。 可以使用此事件执行在 中 ListBox绘制项所需的任务。 如果在属性设置为) 时DrawMode (可变大小的项，则会在绘制项之前引发 事件MeasureItem。DrawMode.OwnerDrawVariable 可以为事件创建事件处理程序， MeasureItem 以指定要在事件事件处理程序 DrawItem 中绘制的项的大小。

有关处理事件的详细信息，请参阅 处理和引发事件。

另请参阅

• OnDrawItem(DrawItemEventArgs)