MeasureItemEventHandler MeasureItemEventHandler MeasureItemEventHandler MeasureItemEventHandler Delegate

定义

表示将处理 ListBoxComboBoxCheckedListBoxMenuItem 控件的 MeasureItem 事件的方法。Represents the method that will handle the MeasureItem event of the ListBox, ComboBox, CheckedListBox, or MenuItem controls.

public delegate void MeasureItemEventHandler(System::Object ^ sender, MeasureItemEventArgs ^ e);
public delegate void MeasureItemEventHandler(object sender, MeasureItemEventArgs e);
type MeasureItemEventHandler = delegate of obj * MeasureItemEventArgs -> unit
Public Delegate Sub MeasureItemEventHandler(sender As Object, e As MeasureItemEventArgs)

参数

sender
Object Object Object Object

事件源。The source of the event.

继承
MeasureItemEventHandlerMeasureItemEventHandlerMeasureItemEventHandlerMeasureItemEventHandler

示例

下面的代码示例演示了如何使用Graphics属性来执行中的项的自定义绘制ListBoxThe following code example demonstrates using the Graphics property to perform custom drawing of the items in a ListBox.

public ref class Form1: public System::Windows::Forms::Form
{
private:
   System::Windows::Forms::ListBox^ listBox1;
   System::ComponentModel::Container^ components;

public:
   ~Form1()
   {
      if ( components != nullptr )
      {
         delete components;
      }
   }

private:

   /// <summary>
   /// Required method for Designer support - do not modify
   /// the contents of this method with the code editor.
   /// </summary>
   void InitializeComponent()
   {
      this->listBox1 = gcnew System::Windows::Forms::ListBox;
      this->SuspendLayout();

      // 
      // listBox1
      // 
      this->listBox1->DrawMode = System::Windows::Forms::DrawMode::OwnerDrawVariable;
      this->listBox1->Location = System::Drawing::Point( 16, 48 );
      this->listBox1->Name = "listBox1";
      this->listBox1->SelectionMode = System::Windows::Forms::SelectionMode::MultiExtended;
      this->listBox1->Size = System::Drawing::Size( 256, 134 );
      this->listBox1->TabIndex = 0;
      this->listBox1->MeasureItem += gcnew System::Windows::Forms::MeasureItemEventHandler( this, &Form1::listBox1_MeasureItem );
      this->listBox1->DrawItem += gcnew System::Windows::Forms::DrawItemEventHandler( this, &Form1::listBox1_DrawItem );

      // 
      // Form1
      // 
      this->ClientSize = System::Drawing::Size( 292, 273 );
      array<System::Windows::Forms::Control^>^temp0 = {this->listBox1};
      this->Controls->AddRange( temp0 );
      this->Name = "Form1";
      this->Text = "Form1";
      this->ResumeLayout( false );
   }

   void listBox1_MeasureItem( Object^ /*sender*/, MeasureItemEventArgs^ e )
   {
      System::Drawing::Font^ font = (dynamic_cast<ListBoxFontItem^>(listBox1->Items[ e->Index ]))->Font;
      SizeF stringSize = e->Graphics->MeasureString( font->Name, font );
      
      // Set the height and width of the item
      e->ItemHeight = (int)stringSize.Height;
      e->ItemWidth = (int)stringSize.Width;
   }

   // For efficiency, cache the brush to use for drawing.
   SolidBrush^ foreColorBrush;
   void listBox1_DrawItem( Object^ /*sender*/, DrawItemEventArgs^ e )
   {
      Brush^ brush;

      // Create the brush using the ForeColor specified by the DrawItemEventArgs
      if ( foreColorBrush == nullptr )
            foreColorBrush = gcnew SolidBrush( e->ForeColor );
      else
      if ( foreColorBrush->Color != e->ForeColor )
      {
         // The control's ForeColor has changed, so dispose of the cached brush and
         // create a new one.
         delete foreColorBrush;
         foreColorBrush = gcnew SolidBrush( e->ForeColor );
      }

      // Select the appropriate brush depending on if the item is selected.
      // Since State can be a combinateion (bit-flag) of enum values, you can't use
      // "==" to compare them.
      if ( (e->State & DrawItemState::Selected) == DrawItemState::Selected )
            brush = SystemBrushes::HighlightText;
      else
            brush = foreColorBrush;

      // Perform the painting.
      System::Drawing::Font^ font = (dynamic_cast<ListBoxFontItem^>(listBox1->Items[ e->Index ]))->Font;
      e->DrawBackground();
      e->Graphics->DrawString( font->Name, font, brush, e->Bounds );
      e->DrawFocusRectangle();
   }

public:

   /// <summary>
   ///  A wrapper class for use with storing Fonts in a ListBox.  Since ListBox uses the
   ///  ToString() of its items for the text it displays, this class is needed to return
   ///  the name of the font, rather than its ToString() value.
   /// </summary>
   ref class ListBoxFontItem
   {
   public:
      System::Drawing::Font^ Font;
      ListBoxFontItem( System::Drawing::Font^ f )
      {
         Font = f;
      }

      virtual String^ ToString() override
      {
         return Font->Name;
      }
   };
};

[STAThread]
int main()
{
   Application::Run( gcnew Form1 );
}
 public class Form1 : System.Windows.Forms.Form
 {
    private System.Windows.Forms.ListBox listBox1;
    private System.ComponentModel.Container components = null;


    protected override void Dispose(bool disposing)
    {
       if( disposing )
       {
          if ( components != null ) 
             components.Dispose();

          if ( foreColorBrush != null )
             foreColorBrush.Dispose();
       }
       base.Dispose(disposing);
    }

#region Windows Form Designer generated code
    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
       this.listBox1 = new System.Windows.Forms.ListBox();
       this.SuspendLayout();
       // 
       // listBox1
       // 
       this.listBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawVariable;
       this.listBox1.Location = new System.Drawing.Point(16, 48);
       this.listBox1.Name = "listBox1";
       this.listBox1.SelectionMode = System.Windows.Forms.SelectionMode.MultiExtended;
       this.listBox1.Size = new System.Drawing.Size(256, 134);
       this.listBox1.TabIndex = 0;
       this.listBox1.MeasureItem += new System.Windows.Forms.MeasureItemEventHandler(this.listBox1_MeasureItem);
       this.listBox1.DrawItem += new System.Windows.Forms.DrawItemEventHandler(this.listBox1_DrawItem);
       // 
       // Form1
       // 
       this.ClientSize = new System.Drawing.Size(292, 273);
       this.Controls.AddRange(new System.Windows.Forms.Control[] {
                                                                    this.listBox1});
       this.Name = "Form1";
       this.Text = "Form1";
       this.ResumeLayout(false);

    }
#endregion

    [STAThread]
    static void Main() 
    {
       Application.Run(new Form1());
    }

    private void listBox1_MeasureItem(object sender, System.Windows.Forms.MeasureItemEventArgs e)
    {
       Font font = ((ListBoxFontItem)listBox1.Items[e.Index]).Font;
       SizeF stringSize = e.Graphics.MeasureString(font.Name, font);

       // Set the height and width of the item
       e.ItemHeight = (int)stringSize.Height;
       e.ItemWidth = (int)stringSize.Width;
    }

    // For efficiency, cache the brush to use for drawing.
    private SolidBrush foreColorBrush;

    private void listBox1_DrawItem(object sender, System.Windows.Forms.DrawItemEventArgs e)
    {
       Brush brush;

       // Create the brush using the ForeColor specified by the DrawItemEventArgs
       if ( foreColorBrush == null )
          foreColorBrush = new SolidBrush(e.ForeColor);
       else if ( foreColorBrush.Color != e.ForeColor )
       {
          // The control's ForeColor has changed, so dispose of the cached brush and
          // create a new one.
          foreColorBrush.Dispose();
          foreColorBrush = new SolidBrush(e.ForeColor);
       }

       // Select the appropriate brush depending on if the item is selected.
       // Since State can be a combinateion (bit-flag) of enum values, you can't use
       // "==" to compare them.
       if ( (e.State & DrawItemState.Selected) == DrawItemState.Selected )
          brush = SystemBrushes.HighlightText;
       else
          brush = foreColorBrush;

       // Perform the painting.
       Font font = ((ListBoxFontItem)listBox1.Items[e.Index]).Font;
       e.DrawBackground();
       e.Graphics.DrawString(font.Name, font, brush, e.Bounds);
       e.DrawFocusRectangle();
    }

    /// <summary>
    ///  A wrapper class for use with storing Fonts in a ListBox.  Since ListBox uses the
    ///  ToString() of its items for the text it displays, this class is needed to return
    ///  the name of the font, rather than its ToString() value.
    /// </summary>
    public class ListBoxFontItem 
    {
       public Font Font;

       public ListBoxFontItem(Font f) 
       {
          Font = f;
       }

       public override string ToString() 
       {
          return Font.Name;
       }
    }
 }
Public Class Form1
   Inherits System.Windows.Forms.Form
   Private WithEvents listBox1 As System.Windows.Forms.ListBox
   Private components As System.ComponentModel.Container = Nothing

   Private FontSize As Single = 12.0F

   '
   '  This sample displays a ListBox that contains a list of all the fonts
   '  installed on the system and draws each item in its respective font.
   '
   Public Sub New()
      InitializeComponent()

      ' Populate control with the fonts installed on the system.
      Dim families As FontFamily() = FontFamily.Families

      Dim family As FontFamily
      For Each family In families
         Dim style As FontStyle = FontStyle.Regular

         ' Monotype Corsiva is only available in italic
         If family.Name = "Monotype Corsiva" Then
            style = style Or FontStyle.Italic
         End If

         listBox1.Items.Add(New ListBoxFontItem(New Font(family.Name, FontSize, style, GraphicsUnit.Point)))
      Next family
   End Sub


   Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
      If disposing Then
         If (components IsNot Nothing) Then
            components.Dispose()
         End If

         If (foreColorBrush IsNot Nothing) Then
            foreColorBrush.Dispose()
         End If
      End If

      MyBase.Dispose(disposing)
   End Sub

   Private Sub InitializeComponent()
      Me.listBox1 = New System.Windows.Forms.ListBox()
      Me.SuspendLayout()
      ' 
      ' listBox1
      ' 
      Me.listBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawVariable
      Me.listBox1.Location = New System.Drawing.Point(16, 48)
      Me.listBox1.Name = "listBox1"
      Me.listBox1.SelectionMode = System.Windows.Forms.SelectionMode.MultiExtended
      Me.listBox1.Size = New System.Drawing.Size(256, 134)
      Me.listBox1.TabIndex = 0
      ' 
      ' Form1
      ' 
      Me.ClientSize = New System.Drawing.Size(292, 273)
      Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.listBox1})
      Me.Name = "Form1"
      Me.Text = "Form1"
      Me.ResumeLayout(False)
   End Sub

   <STAThread()> Shared Sub Main()
      Application.Run(New Form1())
   End Sub

   Private Sub listBox1_MeasureItem(ByVal sender As Object, ByVal e As System.Windows.Forms.MeasureItemEventArgs) Handles listBox1.MeasureItem
      Dim font As Font = CType(listBox1.Items(e.Index), ListBoxFontItem).Font
      Dim stringSize As SizeF = e.Graphics.MeasureString(font.Name, font)

      ' Set the height and width of the item
      e.ItemHeight = CInt(stringSize.Height)
      e.ItemWidth = CInt(stringSize.Width)
   End Sub

   ' For efficiency, cache the brush used for drawing.
   Private foreColorBrush As SolidBrush

   Private Sub listBox1_DrawItem(ByVal sender As Object, ByVal e As System.Windows.Forms.DrawItemEventArgs) Handles listBox1.DrawItem
      Dim brush As Brush

      ' Create the brush using the ForeColor specified by the DrawItemEventArgs
      If foreColorBrush Is Nothing Then
         foreColorBrush = New SolidBrush(e.ForeColor)
      Else
         If Not foreColorBrush.Color.Equals(e.ForeColor) Then
            ' The control's ForeColor has changed, so dispose of the cached brush and
            ' create a new one.
            foreColorBrush.Dispose()
            foreColorBrush = New SolidBrush(e.ForeColor)
         End If
      End If

      ' Select the appropriate brush depending on if the item is selected.
      ' Since State can be a combinateion (bit-flag) of enum values, you can't use
      ' "==" to compare them.
      If (e.State And DrawItemState.Selected) = DrawItemState.Selected Then
         brush = SystemBrushes.HighlightText
      Else
         brush = foreColorBrush
      End If

      ' Perform the painting.
      Dim font As Font = CType(listBox1.Items(e.Index), ListBoxFontItem).Font
      e.DrawBackground()
      e.Graphics.DrawString(font.Name, font, brush, e.Bounds.X, e.Bounds.Y)
      e.DrawFocusRectangle()
   End Sub

   '
   '  A wrapper class for use with storing Fonts in a ListBox.  Since ListBox uses the
   '  ToString() of its items for the text it displays, this class is needed to return
   '  the name of the font, rather than its ToString() value.
   '
   Public Class ListBoxFontItem
      Public Font As Font

      Public Sub New(ByVal f As Font)
         Font = f
      End Sub

      Public Overrides Function ToString() As String
         Return Font.Name
      End Function
   End Class
End Class

注解

创建 MeasureItemEventHandler 委托时,需要标识将处理该事件的方法。When you create a MeasureItemEventHandler delegate, you identify the method that will handle the event. 若要将事件与事件处理程序关联,请将该委托的一个实例添加到事件中。To associate the event with your event handler, add an instance of the delegate to the event. 除非移除了该委托,否则每当发生该事件时就会调用事件处理程序。The event handler is called whenever the event occurs, unless you remove the delegate. 有关事件处理程序委托的详细信息,请参阅处理和引发事件For more information about event handler delegates, see Handling and Raising Events.

扩展方法

GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。Gets an object that represents the method represented by the specified delegate.

适用于

另请参阅