ComboBox.DrawItem 事件

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

Source:

ComboBox.cs

在所有者绘制的 ComboBox 的可视方位更改时发生。

C#

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

事件类型

DrawItemEventHandler

示例

下面的代码示例演示如何通过将 属性OwnerDrawnVariable设置为 DrawMode 并处理 DrawItem 和 MeasureItem 事件来创建所有者绘制的组合框。 它还演示了设置 DropDownWidth 和 DropDownStyle 属性。 若要运行该示例，请将以下代码粘贴到窗体中。 InitializeComboBox在窗体的构造函数或Load事件中调用 方法。

C#

  internal System.Windows.Forms.ComboBox ComboBox1;
  private string[] animals;

  // 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 void InitializeComboBox()
  {
      this.ComboBox1 = new ComboBox();
      this.ComboBox1.DrawMode = 
          System.Windows.Forms.DrawMode.OwnerDrawVariable;
      this.ComboBox1.Location = new System.Drawing.Point(10, 20);
      this.ComboBox1.Name = "ComboBox1";
      this.ComboBox1.Size = new System.Drawing.Size(100, 120);
      this.ComboBox1.DropDownWidth = 250;
      this.ComboBox1.TabIndex = 0;
      this.ComboBox1.DropDownStyle = ComboBoxStyle.DropDown;
      animals = new string[]{"Elephant", "c r o c o d i l e", "lion"};
      ComboBox1.DataSource = animals;
      this.Controls.Add(this.ComboBox1);

      // Hook up the MeasureItem and DrawItem events
      this.ComboBox1.DrawItem += 
          new DrawItemEventHandler(ComboBox1_DrawItem);
      this.ComboBox1.MeasureItem += 
          new MeasureItemEventHandler(ComboBox1_MeasureItem);
  }

  // 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 void ComboBox1_MeasureItem(object sender, 
      System.Windows.Forms.MeasureItemEventArgs e)
  {

      switch(e.Index)
      {
          case 0:
              e.ItemHeight = 45;
              break;
          case 1:
              e.ItemHeight = 20;
              break;
          case 2:
              e.ItemHeight = 35;
              break;
      }
      e.ItemWidth = 260;
  }

  // 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 void ComboBox1_DrawItem(object sender, 
      System.Windows.Forms.DrawItemEventArgs e)
  {

      float size = 0;
      System.Drawing.Font myFont;
      FontFamily family = null;

      System.Drawing.Color animalColor = new System.Drawing.Color();
      switch(e.Index)
      {
          case 0:
              size = 30;
              animalColor = System.Drawing.Color.Gray;
              family = FontFamily.GenericSansSerif;
              break;
          case 1:
              size = 10;
              animalColor = System.Drawing.Color.LawnGreen;
              family = FontFamily.GenericMonospace;
              break;
          case 2:
              size = 15;
              animalColor = System.Drawing.Color.Tan;
              family = FontFamily.GenericSansSerif;
              break;
      }

      // 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.
      Rectangle 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();
  }

注解

此事件由所有者绘制 ComboBox的 使用。 可以使用此事件执行在 中 ComboBox绘制项所需的任务。 如果在将 属性设置为 OwnerDrawVariable) 的值时ComboBox.DrawMode (一个大小可变的System.Windows.Forms.DrawMode项，则会在绘制项之前引发 事件MeasureItem。 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。

适用于