ComboBox.DropDownStyle 属性

获取或设置指定组合框样式的值。

**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）

语法

声明
Public Property DropDownStyle As ComboBoxStyle
用法
Dim instance As ComboBox
Dim value As ComboBoxStyle

value = instance.DropDownStyle

instance.DropDownStyle = value

public ComboBoxStyle DropDownStyle { get; set; }

public:
property ComboBoxStyle DropDownStyle {
    ComboBoxStyle get ();
    void set (ComboBoxStyle value);
}

/** @property */
public ComboBoxStyle get_DropDownStyle ()

/** @property */
public void set_DropDownStyle (ComboBoxStyle value)

public function get DropDownStyle () : ComboBoxStyle

public function set DropDownStyle (value : ComboBoxStyle)

属性值

ComboBoxStyle 值之一。默认为 DropDown。

异常

异常类型	条件
InvalidEnumArgumentException	分配的值不是 ComboBoxStyle 值之一。

备注

DropDownStyle 属性控制显示给用户的界面。可以输入一个值，该值提供以下功能：简单的下拉列表框（始终显示列表）、下拉列表框（文本部分不可编辑，并且必须选择一个箭头才能查看下拉列表框）或默认下拉列表框（文本部分可编辑，并且用户必须按箭头键才能查看列表）。若要始终显示用户不能编辑的列表，请使用 ListBox 控件。

如果将 DropDownStyle 属性设置为 DropDownList，则只能从列表中选择有效值。如果将 DropDownStyle 属性设置为 DropDown，则可以在 ComboBox 的可编辑区域内键入任何值。这种情况下，AutoCompleteMode 的 Append 值与 AutoCompleteMode 的 SuggestAppend 值作用相同。

示例

下面的代码示例演示如何创建所有者描述的组合框，具体方法为将 DrawMode 属性设置为 OwnerDrawnVariable，并处理 DrawItem 和 MeasureItem 事件。它还阐释了如何设置 DropDownWidth 和 DropDownStyle 属性。要运行该示例，请将以下代码粘贴到一个窗体中。在该窗体的构造函数或 Load 事件中调用 InitializeComboBox 方法。

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

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();
}

internal:
   System::Windows::Forms::ComboBox^ ComboBox1;

private:
   array<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.
   void InitializeComboBox()
   {
      this->ComboBox1 = gcnew ComboBox;
      this->ComboBox1->DrawMode = System::Windows::Forms::DrawMode::OwnerDrawVariable;
      this->ComboBox1->Location = System::Drawing::Point( 10, 20 );
      this->ComboBox1->Name = "ComboBox1";
      this->ComboBox1->Size = System::Drawing::Size( 100, 120 );
      this->ComboBox1->DropDownWidth = 250;
      this->ComboBox1->TabIndex = 0;
      this->ComboBox1->DropDownStyle = ComboBoxStyle::DropDown;
      animals = gcnew array<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 +=
         gcnew DrawItemEventHandler( this, &Form1::ComboBox1_DrawItem );
      this->ComboBox1->MeasureItem +=
         gcnew MeasureItemEventHandler( this, &Form1::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;
   }

private:
   // 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.
   void ComboBox1_DrawItem( Object^ sender,
      System::Windows::Forms::DrawItemEventArgs^ e )
   {
      float size = 0;
      System::Drawing::Font^ myFont;
      FontFamily^ family = nullptr;

      System::Drawing::Color animalColor;
      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 = Rectangle( 2, e->Bounds.Top + 2,
         e->Bounds.Height, e->Bounds.Height - 4 );
      e->Graphics->FillRectangle( gcnew SolidBrush( animalColor ), rectangle );
      
      // Draw each string in the array, using a different size, color,
      // and font for each item.
      myFont = gcnew System::Drawing::Font( family, size, FontStyle::Bold );
      e->Graphics->DrawString( animals[ e->Index ], myFont,
         System::Drawing::Brushes::Black, 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();
   }

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.set_DrawMode(
        System.Windows.Forms.DrawMode.OwnerDrawVariable);
    this.comboBox1.set_Location(new System.Drawing.Point(10, 20));
    this.comboBox1.set_Name("comboBox1");
    this.comboBox1.set_Size(new System.Drawing.Size(100, 120));
    this.comboBox1.set_DropDownWidth(250);
    this.comboBox1.set_TabIndex(0);
    this.comboBox1.set_DropDownStyle(ComboBoxStyle.DropDown);
    animals = new String[] { "Elephant", "c r o c o d i l e", "lion" };
    comboBox1.set_DataSource(animals);
    this.get_Controls().Add(this.comboBox1);
    // Hook up the MeasureItem and DrawItem events
    this.comboBox1.add_DrawItem(
        new DrawItemEventHandler(comboBox1_DrawItem));
    this.comboBox1.add_MeasureItem(
        new MeasureItemEventHandler(comboBox1_MeasureItem));
} //InitializeComboBox

// 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.get_Index()) {
        case 0:
            e.set_ItemHeight(45);
            break;

        case 1:
            e.set_ItemHeight(20);
            break;

        case 2:
            e.set_ItemHeight(35);
            break;
    }
    e.set_ItemWidth(260);
} //comboBox1_MeasureItem

// 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.get_Index()) {
        case 0:
            size = 30;
            animalColor = System.Drawing.Color.get_Gray();
            family = FontFamily.get_GenericSansSerif();
            break;

        case 1:
            size = 10;
            animalColor = System.Drawing.Color.get_LawnGreen();
            family = FontFamily.get_GenericMonospace();
            break;

        case 2:
            size = 15;
            animalColor = System.Drawing.Color.get_Tan();
            family = FontFamily.get_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.get_Bounds().get_Top() + 2, 
        e.get_Bounds().get_Height(),
        e.get_Bounds().get_Height() - 4);
    e.get_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.get_Graphics().DrawString((String)animals.get_Item(e.get_Index()), 
        myFont, System.Drawing.Brushes.get_Black(), 
        new RectangleF(e.get_Bounds().get_X() + rectangle.get_Width(),
        e.get_Bounds().get_Y(), e.get_Bounds().get_Width(),
        e.get_Bounds().get_Height()));
    // Draw the focus rectangle if the mouse hovers over an item.
    e.DrawFocusRectangle();
} //comboBox1_DrawItem

平台

Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition

.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。

版本信息

.NET Framework

受以下版本支持：2.0、1.1、1.0

.NET Compact Framework

受以下版本支持：2.0、1.0

请参见

参考

ComboBox 类
ComboBox 成员
System.Windows.Forms 命名空间
ComboBoxStyle