ListBox.MeasureItem-Ereignis

Tritt ein, wenn eine Ownerdrawn-ListBox erstellt und die Größe der einzelnen Listenelemente bestimmt wird.

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

Syntax

'Declaration
Public Event MeasureItem As MeasureItemEventHandler
'Usage
Dim instance As ListBox
Dim handler As MeasureItemEventHandler

AddHandler instance.MeasureItem, handler

public event MeasureItemEventHandler MeasureItem

public:
event MeasureItemEventHandler^ MeasureItem {
    void add (MeasureItemEventHandler^ value);
    void remove (MeasureItemEventHandler^ value);
}

/** @event */
public void add_MeasureItem (MeasureItemEventHandler value)

/** @event */
public void remove_MeasureItem (MeasureItemEventHandler value)

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

Hinweise

Sie können einen Ereignishandler für dieses Ereignis erstellen, um anzugeben, auf welche Größe ein Element vergrößert wird, bevor es im DrawItem-Ereignis gezeichnet wird. Das Ereignis wird nur ausgelöst, wenn die DrawMode-Eigenschaft auf OwnerDrawVariable festgelegt ist.

Die maximale Höhe eines ListBox-Elements beträgt 255 Pixel. Das Festlegen der ItemHeight-Eigenschaft der MeasureItemEventArgs auf einen höheren Wert als 255 beim Behandeln dieses Ereignisses führt u. U. zu unerwarteten Ergebnissen.

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

Beispiel

Im folgenden Codebeispiel wird eine Ownerdrawn-ListBox durch Festlegen der DrawMode-Eigenschaft auf OwnerDrawVariable und durch Behandeln des DrawItem-Ereignisses und des MeasureItem-Ereignisses veranschaulicht. Außerdem werden das Festlegen der BorderStyle-Eigenschaft und der ScrollAlwaysVisible-Eigenschaft sowie das Verwenden der AddRange-Methode dargestellt.

Wenn Sie das Beispiel ausführen möchten, fügen Sie es in ein leeres Formular ein, in das der System.Drawing-Namespace und der System.Windows.Forms-Namespace importiert werden. Rufen Sie InitializeOwnerDrawnListBox im Konstruktor oder in der Load-Ereignisbehandlungsmethode des Formulars auf.

Friend WithEvents ListBox1 As System.Windows.Forms.ListBox

Private Sub InitializeOwnerDrawnListBox()
    Me.ListBox1 = New System.Windows.Forms.ListBox

    ' Set the location and size.
    ListBox1.Location = New Point(20, 20)
    ListBox1.Size = New Size(240, 240)

    ' Populate the ListBox.ObjectCollection property 
    ' with several strings, using the AddRange method.
    Me.ListBox1.Items.AddRange(New Object() _
        {"System.Windows.Forms", "System.Drawing", "System.Xml", _
        "System.Net", "System.Runtime.Remoting", "System.Web"})

    ' Turn off the scrollbar.
    ListBox1.ScrollAlwaysVisible = False

    ' Set the border style to a single, flat border.
    ListBox1.BorderStyle = BorderStyle.FixedSingle

    ' Set the DrawMode property to the OwnerDrawVariable value. 
    ' This means the MeasureItem and DrawItem events must be 
    ' handled.
    ListBox1.DrawMode = DrawMode.OwnerDrawVariable
    Me.Controls.Add(Me.ListBox1)
End Sub


' Handle the DrawItem event for an owner-drawn ListBox.
Private Sub ListBox1_DrawItem(ByVal sender As Object, _
    ByVal e As DrawItemEventArgs) Handles ListBox1.DrawItem

    ' If the item is the selected item, then draw the rectangle filled in
    ' blue. The item is selected when a bitwise And of the State property
    ' and the DrawItemState.Selected property is true. 
    If (e.State And DrawItemState.Selected = DrawItemState.Selected) Then
        e.Graphics.FillRectangle(Brushes.CornflowerBlue, e.Bounds)
    Else
        ' Otherwise, draw the rectangle filled in beige.
        e.Graphics.FillRectangle(Brushes.Beige, e.Bounds)
    End If

    ' Draw a rectangle in blue around each item.
    e.Graphics.DrawRectangle(Pens.Blue, e.Bounds)

    ' Draw the text in the item.
    e.Graphics.DrawString(Me.ListBox1.Items(e.Index), Me.Font, _
        Brushes.Black, e.Bounds.X, e.Bounds.Y)

    ' Draw the focus rectangle around the selected item.
    e.DrawFocusRectangle()
End Sub

' Handle the MeasureItem event for an owner-drawn ListBox.
Private Sub ListBox1_MeasureItem(ByVal sender As Object, _
    ByVal e As MeasureItemEventArgs) Handles ListBox1.MeasureItem

    ' Cast the sender object back to ListBox type.
    Dim theListBox As ListBox = CType(sender, ListBox)

    ' Get the string contained in each item.
    Dim itemString As String = CType(theListBox.Items(e.Index), String)

    ' Split the string at the " . "  character.
    Dim resultStrings() As String = itemString.Split(".")

    ' If the string contains more than one period, increase the 
    ' height by ten pixels; otherwise, increase the height by 
    ' five pixels.
    If (resultStrings.Length > 2) Then
        e.ItemHeight += 10
    Else
        e.ItemHeight += 5
    End If

End Sub

internal System.Windows.Forms.ListBox ListBox1;

private void InitializeOwnerDrawnListBox()
{
    this.ListBox1 = new System.Windows.Forms.ListBox();

    // Set the location and size.
    ListBox1.Location = new Point(20, 20);
    ListBox1.Size = new Size(240, 240);

    // Populate the ListBox.ObjectCollection property 
    // with several strings, using the AddRange method.
    this.ListBox1.Items.AddRange(new object[]{"System.Windows.Forms", 
        "System.Drawing", "System.Xml", "System.Net", "System.Runtime.Remoting", 
        "System.Web"});

    // Turn off the scrollbar.
    ListBox1.ScrollAlwaysVisible = false;

    // Set the border style to a single, flat border.
    ListBox1.BorderStyle = BorderStyle.FixedSingle;

    // Set the DrawMode property to the OwnerDrawVariable value. 
    // This means the MeasureItem and DrawItem events must be 
    // handled.
    ListBox1.DrawMode = DrawMode.OwnerDrawVariable;
    ListBox1.MeasureItem += 
        new MeasureItemEventHandler(ListBox1_MeasureItem);
    ListBox1.DrawItem += new DrawItemEventHandler(ListBox1_DrawItem);
    this.Controls.Add(this.ListBox1);
    
}


// Handle the DrawItem event for an owner-drawn ListBox.
private void ListBox1_DrawItem(object sender, DrawItemEventArgs e)
{

    // If the item is the selected item, then draw the rectangle
    // filled in blue. The item is selected when a bitwise And  
    // of the State property and the DrawItemState.Selected 
    // property is true.
    if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
    {
        e.Graphics.FillRectangle(Brushes.CornflowerBlue, e.Bounds);
    }
    else
    {
        // Otherwise, draw the rectangle filled in beige.
        e.Graphics.FillRectangle(Brushes.Beige, e.Bounds);
    }

    // Draw a rectangle in blue around each item.
    e.Graphics.DrawRectangle(Pens.Blue, e.Bounds);

    // Draw the text in the item.
    e.Graphics.DrawString(ListBox1.Items[e.Index].ToString(),
        this.Font, Brushes.Black, e.Bounds.X, e.Bounds.Y);

    // Draw the focus rectangle around the selected item.
    e.DrawFocusRectangle();
}

// Handle the MeasureItem event for an owner-drawn ListBox.
private void ListBox1_MeasureItem(object sender, 
    MeasureItemEventArgs e)
{

    // Cast the sender object back to ListBox type.
    ListBox theListBox = (ListBox) sender;

    // Get the string contained in each item.
    string itemString = (string) theListBox.Items[e.Index];

    // Split the string at the " . "  character.
    string[] resultStrings = itemString.Split('.');

    // If the string contains more than one period, increase the 
    // height by ten pixels; otherwise, increase the height by 
    // five pixels.
    if (resultStrings.Length>2)
    {
        e.ItemHeight += 10;
    }
    else
    {
        e.ItemHeight += 5;
    }

}

internal:
   System::Windows::Forms::ListBox^ ListBox1;

private:
   void InitializeOwnerDrawnListBox()
   {
      this->ListBox1 = gcnew System::Windows::Forms::ListBox;
      
      // Set the location and size.
      ListBox1->Location = Point(20,20);
      ListBox1->Size = System::Drawing::Size( 240, 240 );
      
      // Populate the ListBox.ObjectCollection property 
      // with several strings, using the AddRange method.
      array<Object^>^temp0 = {"System.Windows.Forms","System.Drawing","System.Xml","System.Net","System.Runtime.Remoting","System.Web"};
      this->ListBox1->Items->AddRange( temp0 );
      
      // Turn off the scrollbar.
      ListBox1->ScrollAlwaysVisible = false;
      
      // Set the border style to a single, flat border.
      ListBox1->BorderStyle = BorderStyle::FixedSingle;
      
      // Set the DrawMode property to the OwnerDrawVariable value. 
      // This means the MeasureItem and DrawItem events must be 
      // handled.
      ListBox1->DrawMode = DrawMode::OwnerDrawVariable;
      ListBox1->MeasureItem += gcnew MeasureItemEventHandler( this, &Form1::ListBox1_MeasureItem );
      ListBox1->DrawItem += gcnew DrawItemEventHandler( this, &Form1::ListBox1_DrawItem );
      this->Controls->Add( this->ListBox1 );
   }

   // Handle the DrawItem event for an owner-drawn ListBox.
   void ListBox1_DrawItem( Object^ /*sender*/, DrawItemEventArgs^ e )
   {
      // If the item is the selected item, then draw the rectangle
      // filled in blue. The item is selected when a bitwise And  
      // of the State property and the DrawItemState.Selected 
      // property is true.
      if ( (e->State & DrawItemState::Selected) == DrawItemState::Selected )
      {
         e->Graphics->FillRectangle( Brushes::CornflowerBlue, e->Bounds );
      }
      else
      {
         
         // Otherwise, draw the rectangle filled in beige.
         e->Graphics->FillRectangle( Brushes::Beige, e->Bounds );
      }
      
      // Draw a rectangle in blue around each item.
      e->Graphics->DrawRectangle( Pens::Blue, e->Bounds );
      
      // Draw the text in the item.
      e->Graphics->DrawString( ListBox1->Items[ e->Index ]->ToString(), this->Font, Brushes::Black, (float)e->Bounds.X, (float)e->Bounds.Y );
      
      // Draw the focus rectangle around the selected item.
      e->DrawFocusRectangle();
   }


   // Handle the MeasureItem event for an owner-drawn ListBox.
   void ListBox1_MeasureItem( Object^ sender, MeasureItemEventArgs^ e )
   {
      
      // Cast the sender object back to ListBox type.
      ListBox^ theListBox = dynamic_cast<ListBox^>(sender);
      
      // Get the string contained in each item.
      String^ itemString = dynamic_cast<String^>(theListBox->Items[ e->Index ]);
      
      // Split the string at the " . "  character.
      array<Char>^temp1 = {'.'};
      array<String^>^resultStrings = itemString->Split( temp1 );
      
      // If the string contains more than one period, increase the 
      // height by ten pixels; otherwise, increase the height by 
      // five pixels.
      if ( resultStrings->Length > 2 )
      {
         e->ItemHeight += 10;
      }
      else
      {
         e->ItemHeight += 5;
      }
   }

private System.Windows.Forms.ListBox listBox1;

private void InitializeOwnerDrawnListBox()
{
    this.listBox1 = new System.Windows.Forms.ListBox();
    // Set the location and size.
    listBox1.set_Location(new Point(20, 20));
    listBox1.set_Size(new Size(240, 240));
    // Populate the ListBox.ObjectCollection property 
    // with several strings, using the AddRange method.
    this.listBox1.get_Items().AddRange(new Object[] { 
        "System.Windows.Forms", "System.Drawing", 
        "System.Xml", "System.Net", "System.Runtime.Remoting", 
        "System.Web" });
    // Turn off the scrollbar.
    listBox1.set_ScrollAlwaysVisible(false);
    // Set the border style to a single, flat border.
    listBox1.set_BorderStyle(BorderStyle.FixedSingle);
    // Set the DrawMode property to the OwnerDrawVariable value. 
    // This means the MeasureItem and DrawItem events must be 
    // handled.
    listBox1.set_DrawMode(DrawMode.OwnerDrawVariable);
    listBox1.add_MeasureItem(new MeasureItemEventHandler(
        listBox1_MeasureItem));
    listBox1.add_DrawItem(new DrawItemEventHandler(listBox1_DrawItem));
    this.get_Controls().Add(this.listBox1);
} //InitializeOwnerDrawnListBox

// Handle the DrawItem event for an owner-drawn ListBox.
private void listBox1_DrawItem(Object sender, DrawItemEventArgs e)
{
    // If the item is the selected item, then draw the rectangle
    // filled in blue. The item is selected when a bitwise And  
    // of the State property and the DrawItemState.Selected 
    // property is true.
    if ((e.get_State() & DrawItemState.Selected) 
        == DrawItemState.Selected) {
        e.get_Graphics().FillRectangle(Brushes.get_CornflowerBlue(), 
            e.get_Bounds());
    }
    else {
        // Otherwise, draw the rectangle filled in beige.
        e.get_Graphics().FillRectangle(Brushes.get_Beige(), 
            e.get_Bounds());
    }
    // Draw a rectangle in blue around each item.
    e.get_Graphics().DrawRectangle(Pens.get_Blue(), e.get_Bounds());
    // Draw the text in the item.
    e.get_Graphics().DrawString(listBox1.get_Items().get_Item(
        e.get_Index()).ToString(), this.get_Font(), 
        Brushes.get_Black(), e.get_Bounds().get_X(), 
        e.get_Bounds().get_Y());
    // Draw the focus rectangle around the selected item.
    e.DrawFocusRectangle();
} //listBox1_DrawItem

// Handle the MeasureItem event for an owner-drawn ListBox.
private void listBox1_MeasureItem(Object sender, MeasureItemEventArgs e)
{
    // Cast the sender object back to ListBox type.
    ListBox theListBox = (ListBox) sender;
    // Get the string contained in each item.
    String itemString = (String)(theListBox.get_Items().
           get_Item(e.get_Index()));
    // Split the string at the " . "  character.
    String resultStrings[] = itemString.Split(new char[] { '.' });
    // If the string contains more than one period, increase the 
    // height by ten pixels; otherwise, increase the height by 
    // five pixels.
    if (resultStrings.length > 2) {
        e.set_ItemHeight(e.get_ItemHeight() + 10);
    }
    else {
        e.set_ItemHeight(e.get_ItemHeight() + 5);
    }
} //listBox1_MeasureItem

Plattformen

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, 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

ListBox-Klasse
ListBox-Member
System.Windows.Forms-Namespace
ListBox.ItemHeight-Eigenschaft