ComboBox.DrawItem Ereignis

Definition

Namespace:

System.Windows.Forms

Assembly:

System.Windows.Forms.dll

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

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 

Ereignistyp

DrawItemEventHandler

Beispiele

Im folgenden Codebeispiel wird veranschaulicht, wie Sie ein kombinationsfeld vom Besitzer gezeichnet erstellen, indem Sie die DrawMode -Eigenschaft auf OwnerDrawnVariable und die DrawItem -Ereignisse und -Ereignisse festlegen und MeasureItem behandeln. Außerdem wird das Festlegen der DropDownWidth Eigenschaften und DropDownStyle veranschaulicht. Fügen Sie zum Ausführen des Beispiels den folgenden Code in ein Formular ein. Rufen Sie die InitializeComboBox -Methode im Konstruktor oder Load Ereignis des Formulars auf.

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();
   }

  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();
  }

  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

Hinweise

Dieses Ereignis wird von einem besitzergezeichneten ComboBoxverwendet. Sie können dieses Ereignis verwenden, um die Aufgaben auszuführen, die zum Zeichnen von Elementen in der ComboBoxerforderlich sind. Wenn Sie ein Element mit variabler Größe haben (wenn die ComboBox.DrawMode Eigenschaft auf den OwnerDrawVariable Wert von System.Windows.Forms.DrawModefestgelegt ist), bevor Sie ein Element zeichnen, wird das MeasureItem -Ereignis ausgelöst. Sie können einen Ereignishandler für das MeasureItem Ereignis erstellen, um die Größe des Elements anzugeben, das Sie in Ihrem Ereignishandler für das DrawItem Ereignis zeichnen möchten.

Weitere Informationen zur Behandlung von Ereignissen finden Sie unter behandeln und Auslösen von Ereignissen.