ConditionalWeakTable<TKey,TValue>.CreateValueCallback 代理人

參考

定義

命名空間:: System.Runtime.CompilerServices

組件:: System.Runtime.dll

組件:: mscorlib.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

代表方法，這個方法會建立非預設值，以作為索引鍵/值組的一部分加入 ConditionalWeakTable<TKey,TValue> 物件。

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

參數

key: TKey

屬於所要建立之值的索引鍵。

傳回值

TValue

參考類型的執行個體，代表要附加至所指定索引鍵的值。

範例

下列範例會 MainClass 定義類別和 MainInfo 類別。 MainInfo 提供實例的相關資訊 MainClass 。它也會在 Visual Basic) 方法中 CreateAttachedValue 定義靜態 (Shared ，可以指派給 ConditionalWeakTable<TKey,TValue>.CreateValueCallback 委派並傳遞至 GetValue 方法。此範例會 GetValue 呼叫方法，將物件及其對應的 MainInfo 物件新增 MainClass 至 ConditionalWeakTable<TKey,TValue> 資料表。此範例也會說明對和 GetOrCreateValue 方法的呼叫 Add ，以將索引鍵/值組新增至資料表，以及呼叫 TryGetValue 方法來擷取屬於現有索引鍵的值。

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

備註

委派 ConditionalWeakTable<TKey,TValue>.CreateValueCallback 會封裝在物件中找不到傳遞至方法的索引鍵時，由方法叫用的 ConditionalWeakTable<TKey,TValue> 回呼方法 ConditionalWeakTable<TKey,TValue>.GetValue 。方法 GetValue 會將回呼方法傳遞索引鍵，代表要動態附加屬性值的 Managed 物件。方法負責將屬性值傳回給其呼叫端，進而將索引鍵/值組新增至資料表。

方法 ConditionalWeakTable<TKey,TValue>.CreateValueCallback 可用來傳回可附加至指定索引鍵之參考型別的實例。它可讓該實例使用非預設值初始化。如果資料表中找不到索引鍵，此方法會 ConditionalWeakTable<TKey,TValue>.GetOrCreateValue 新增索引鍵/值組，其中會使用預設值初始化值。

擴充方法

GetMethodInfo(Delegate)

取得表示特定委派所代表之方法的物件。

適用於

另請參閱

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

ConditionalWeakTable<TKey,TValue>.CreateValueCallback 代理人

定義

參數

傳回值

範例

備註

擴充方法

適用於

另請參閱

其他資源