ComboBox.DrawItem-Ereignis

Tritt ein, wenn sich ein Darstellungsaspekt einer Ownerdrawn-ComboBox ändert.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

Syntax

'Declaration
Public Event DrawItem As DrawItemEventHandler
'Usage
Dim instance As ComboBox
Dim handler As DrawItemEventHandler

AddHandler instance.DrawItem, handler

public event DrawItemEventHandler DrawItem

public:
event DrawItemEventHandler^ DrawItem {
    void add (DrawItemEventHandler^ value);
    void remove (DrawItemEventHandler^ value);
}

/** @event */
public void add_DrawItem (DrawItemEventHandler value)

/** @event */
public void remove_DrawItem (DrawItemEventHandler value)

JScript unterstützt die Verwendung von Ereignissen, aber nicht die Deklaration von neuen Ereignissen.

Hinweise

Dieses Ereignis wird von einer Ownerdrawn-ComboBox verwendet. Mithilfe dieses Ereignisses können Sie die Aufgaben durchführen, die zum Zeichnen der Elemente in der ComboBox erforderlich sind. Bei einem Element mit variabler Größe (wenn die ComboBox.DrawMode-Eigenschaft auf den OwnerDrawVariable-Wert von System.Windows.Forms.DrawMode festgelegt ist) wird vor dem Zeichnen eines Elements das MeasureItem-Ereignis ausgelöst. Sie können einen Ereignishandler für das MeasureItem-Ereignis erstellen, um die Größe für das Element anzugeben, das im Ereignishandler für das DrawItem-Ereignis gezeichnet werden soll.

Weitere Informationen zum Behandeln von Ereignissen finden Sie unter Behandeln von Ereignissen.

Beispiel

Im folgenden Codebeispiel wird das Erstellen eines Ownerdrawn-Kombinationsfelds veranschaulicht. Dazu wird die DrawMode-Eigenschaft auf OwnerDrawnVariable festgelegt, und anschließend werden das DrawItem-Ereignis und das MeasureItem-Ereignis behandelt. Außerdem wird gezeigt, wie die DropDownWidth-Eigenschaft und die DropDownStyle-Eigenschaft festgelegt werden. Fügen Sie zum Ausführen des Beispiels den folgenden Code in ein Formular ein. Rufen Sie die InitializeComboBox-Methode im Konstruktor oder im Load-Ereignis des Formulars auf.

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

Plattformen

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.

Versionsinformationen

.NET Framework

Unterstützt in: 2.0, 1.1, 1.0

Siehe auch

Referenz

ComboBox-Klasse
ComboBox-Member
System.Windows.Forms-Namespace