MeasureItemEventArgs Classe

Definizione

Spazio dei nomi:

System.Windows.Forms

Assembly:

System.Windows.Forms.dll

Fornisce i dati per l'evento MeasureItem dei controlli ListBox, ComboBox, CheckedListBox e MenuItem.

public ref class MeasureItemEventArgs : EventArgs

public class MeasureItemEventArgs : EventArgs

type MeasureItemEventArgs = class
    inherit EventArgs

Public Class MeasureItemEventArgs
Inherits EventArgs

Ereditarietà

Object

EventArgs

MeasureItemEventArgs

Esempio

Nell'esempio di codice seguente viene illustrato come utilizzare la Graphics proprietà per eseguire un disegno personalizzato degli elementi in un oggetto 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

Commenti

Questo evento viene inviato quando la OwnerDraw proprietà di ListBox, ComboBox, CheckedListBoxo MenuItem è impostata su true. Viene usato per indicare alla funzione di disegno come ridimensionare un elemento.

Per informazioni sul modello di evento, vedere Gestione e generazione di eventi.

Costruttori

MeasureItemEventArgs(Graphics, Int32)	Inizializza una nuova istanza della classe MeasureItemEventArgs.
MeasureItemEventArgs(Graphics, Int32, Int32)	Inizializza una nuova istanza della classe MeasureItemEventArgs fornendo un parametro per l'altezza dell'elemento.

Proprietà

Graphics	Ottiene l'oggetto Graphics rispetto al quale effettuare la misurazione.
Index	Ottiene l'indice dell'elemento per il quale sono necessarie l'altezza o la larghezza.
ItemHeight	Ottiene o imposta l'altezza dell'elemento specificato dalla proprietà Index.
ItemWidth	Ottiene o imposta la larghezza dell'elemento specificato dalla proprietà Index.

Metodi

Equals(Object)	Determina se l'oggetto specificato è uguale all'oggetto corrente. (Ereditato da Object)
GetHashCode()	Funge da funzione hash predefinita. (Ereditato da Object)
GetType()	Ottiene l'oggetto Type dell'istanza corrente. (Ereditato da Object)
MemberwiseClone()	Crea una copia superficiale dell'oggetto Object corrente. (Ereditato da Object)
ToString()	Restituisce una stringa che rappresenta l'oggetto corrente. (Ereditato da Object)

Vedi anche

• ListBox
• ComboBox
• CheckedListBox
• MenuItem
• MeasureItemEventHandler