ConditionalWeakTable<TKey,TValue>.CreateValueCallback Delegasikan

Definisi

Ruang nama:

System.Runtime.CompilerServices

Rakitan:

System.Runtime.dll

Sumber:

ConditionalWeakTable.cs

Mewakili metode yang membuat nilai non-default untuk ditambahkan sebagai bagian dari pasangan kunci/nilai ke ConditionalWeakTable<TKey,TValue> objek.

public:  where TKey : class where TValue : classdelegate TValue ConditionalWeakTable<TKey, TValue>::CreateValueCallback(TKey key);

public delegate TValue ConditionalWeakTable<TKey,TValue>.CreateValueCallback(TKey key) where TKey : class where TValue : class;

type ConditionalWeakTable<'Key, 'Value (requires 'Key : null and 'Value : null)>.CreateValueCallback = delegate of 'Key -> 'Value

Public Delegate Function ConditionalWeakTable(Of TKey, TValue).CreateValueCallback(key As TKey) As TValue 

Parameter

key

TKey

Kunci yang termasuk dalam nilai yang akan dibuat.

Tampilkan Nilai

TValue

Instans jenis referensi yang mewakili nilai untuk dilampirkan ke kunci yang ditentukan.

Contoh

Contoh berikut mendefinisikan MainClass kelas dan MainInfo kelas. MainInfo memberikan informasi tentang MainClass instans. Ini juga mendefinisikan metode statis (Shared dalam Visual Basic) CreateAttachedValue yang dapat ditetapkan ke ConditionalWeakTable<TKey,TValue>.CreateValueCallback delegasi dan diteruskan ke GetValue metode . Contoh memanggil GetValue metode untuk menambahkan MainClass objek dan objek yang MainInfo sesuai ke ConditionalWeakTable<TKey,TValue> tabel. Contoh ini juga mengilustrasikan panggilan ke Add metode dan GetOrCreateValue untuk menambahkan pasangan kunci/nilai ke tabel, dan panggilan ke TryGetValue metode untuk mengambil nilai milik kunci yang ada.

using System;
using System.Reflection;
using System.Runtime.CompilerServices;

public class Example
{
   string Name; 
   
   public Example(string name)
   {
      this.Name = name;
   }
   
   public override string ToString()
   {
      return this.Name;
   }
}

// Define a class to contain information about each Example instance.
public class ExampleInfo
{
   public string Name;
   public int Methods;
   public int Properties;
   
   public override string ToString()
   {
      return String.Format("{0}: {1} Methods, {2} Properties", 
                           this.Name, this.Methods, this.Properties);
   }
}

public class ExampleTest
{
   private static BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;

   public static void Main()
   {
      Example ex1 = new Example("ex1");
      Example ex2 = new Example("ex2");
      Example ex3 = new Example("ex3");
      
      ExampleInfo exInfo1 = new ExampleInfo(); 
      exInfo1.Name = ex1.ToString();
      exInfo1.Methods = ex1.GetType().GetMethods(flags).Length;
      exInfo1.Properties = ex1.GetType().GetProperties(flags).Length;
      
      ExampleInfo exInfo3 = new ExampleInfo(); 
      exInfo3.Name = ex3.ToString();
      exInfo3.Methods = ex3.GetType().GetMethods(flags).Length;
      exInfo3.Properties = ex3.GetType().GetProperties(flags).Length;

      var attached = new ConditionalWeakTable<Example, ExampleInfo>();
      ExampleInfo value = null;

      // Attach a property to ex1 using the Add method, then retrieve it.
      attached.Add(ex1, exInfo1);
      if (attached.TryGetValue(ex1, out value))
         Console.WriteLine("{0}, {1}", ex1, value);
      else
         Console.WriteLine("{0} does not have an attached property.", ex1);

      // Attempt to retrieve the value attached to ex2.
      value = attached.GetValue(ex2, ExampleTest.CreateAttachedValue);      
      if (attached.TryGetValue(ex2, out value))
         Console.WriteLine("{0}, {1}", ex2, value);
      else 
         Console.WriteLine("{0} does not have an attached property.", ex2);
      
      // Attempt to retrieve the value attached to ex3.
      value = attached.GetOrCreateValue(ex3);
      Console.WriteLine("{0}, {1}", ex3, value);
   }

   public static ExampleInfo CreateAttachedValue(Example ex)
   {
      ExampleInfo info = new ExampleInfo();
      info.Name = ex.ToString();
      info.Methods = ex.GetType().GetMethods(flags).Length;
      info.Properties = ex.GetType().GetProperties(flags).Length;
      return info;
   }
}
// The example displays the following output:
//       ex1, ex1: 4 Methods, 0 Properties
//       ex2, ex2: 4 Methods, 0 Properties
//       ex3, : 0 Methods, 0 Properties

Imports System.Reflection
Imports System.Runtime.CompilerServices

Public Class Example
   Public Name As String
   
   Public Sub New(name As String)
      Me.Name = name
   End Sub
   
   Public Overrides Function ToString() As String
      Return Me.Name
   End Function
End Class

' Define a class to contain information about each Example instance.
Public Class ExampleInfo
   Public Name As String
   Public Methods As Integer
   Public Properties As Integer
   
   Public Overrides Function ToString() As String
      Return String.Format("{0}: {1} Methods, {2} Properties", _
                           Me.Name, Me.Methods, Me.Properties)
   End Function
End Class

Module TestExample

   Private flags As BindingFlags = BindingFlags.Public Or BindingFlags.Instance

   Public Sub Main()
      Dim ex1 As New Example("ex1")
      Dim ex2 As New Example("ex2")
      Dim ex3 As New Example("ex3")
      
      Dim exInfo1 As New ExampleInfo() 
      exInfo1.Name = ex1.ToString()
      exInfo1.Methods = ex1.GetType().GetMethods(flags).Count
      exInfo1.Properties = ex1.GetType().GetProperties(flags).Count
      
      Dim exInfo3 As New ExampleInfo() 
      exInfo3.Name = ex3.ToString()
      exInfo3.Methods = ex3.GetType().GetMethods(flags).Count
      exInfo3.Properties = ex3.GetType().GetProperties(flags).Count

      Dim attached As New ConditionalWeakTable(Of Example, ExampleInfo)
      Dim value As ExampleInfo = Nothing

      ' Attach a property to ex1 using the Add method, then retrieve it.
      attached.Add(ex1, exInfo1)
      If attached.TryGetValue(ex1, value) Then
         Console.WriteLine("{0}, {1}", ex1, value)
      Else
         Console.WriteLine("{0} does not have an attached property.", ex1)
      End If

      ' Attempt to retrieve the value attached to ex2.
      value = attached.GetValue(ex2, AddressOf TestExample.CreateAttachedValue)      
      If attached.TryGetValue(ex2, value) Then
         Console.WriteLine("{0}, {1}", ex2, value)
      Else 
         Console.WriteLine("{0} does not have an attached property.", ex2)
      End If
      
      ' Atttempt to retrieve the value attached to ex3.
      value = attached.GetOrCreateValue(ex3)
      Console.WriteLine("{0}, {1}", ex3, value)
   End Sub
   
   Public Function CreateAttachedValue(ex As Example) As ExampleInfo
      Dim info As New ExampleInfo()
      info.Name = ex.ToString()
      info.Methods = ex.GetType().GetMethods(flags).Count
      info.Properties = ex.GetType().GetProperties(flags).Count
      Return info
   End Function
End Module
' The example displays the following output:
'       ex1, ex1: 4 Methods, 0 Properties
'       ex2, ex2: 4 Methods, 0 Properties
'       ex3, : 0 Methods, 0 Properties

Keterangan

Delegasi ConditionalWeakTable<TKey,TValue>.CreateValueCallback merangkum metode panggilan balik yang dipanggil oleh ConditionalWeakTable<TKey,TValue>.GetValue metode ketika kunci yang diteruskan ke metode tidak ditemukan di ConditionalWeakTable<TKey,TValue> objek . Metode GetValue meneruskan metode panggilan balik kunci yang mewakili objek terkelola tempat nilai properti akan dilampirkan secara dinamis. Metode ini bertanggung jawab untuk mengembalikan nilai properti ke pemanggilnya, yang, pada gilirannya, menambahkan pasangan kunci/nilai ke tabel.

Metode ConditionalWeakTable<TKey,TValue>.CreateValueCallback ini digunakan untuk mengembalikan instans jenis referensi yang dapat dilampirkan ke kunci yang ditentukan. Ini memungkinkan instans tersebut diinisialisasi menggunakan nilai non-default. Jika kunci tidak ditemukan dalam tabel, ConditionalWeakTable<TKey,TValue>.GetOrCreateValue metode menambahkan pasangan kunci/nilai di mana nilai diinisialisasi menggunakan nilai default.

Metode Ekstensi

GetMethodInfo(Delegate)

Mendapatkan objek yang mewakili metode yang diwakili oleh delegasi yang ditentukan.

Lihat juga

• GetValue(TKey, ConditionalWeakTable<TKey,TValue>.CreateValueCallback)