ConditionalWeakTable<TKey, TValue>.GetValue Method

Parameters

• key
  Type: TKey
  The key to search for. key represents the object to which the property is attached.

• createValueCallback
  Type: System.Runtime.CompilerServices.ConditionalWeakTable<TKey, TValue>.CreateValueCallback
  A delegate to a method that can create a value for the given key. It has a single parameter of type TKey, and returns a value of type TValue.

Return Value

Type: TValue
The value attached to key, if key already exists in the table; otherwise, the new value returned by the createValueCallback delegate.

Imports System.Reflection
Imports System.Runtime.CompilerServices

Public Class MainClass
   Public Name As String

   Public Sub New(ByVal 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 MainClass instance.
Public Class MainInfo
   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 Example
   Private flags As BindingFlags = BindingFlags.Public Or BindingFlags.Instance

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim m1 As New MainClass("m1")
      Dim m2 As New MainClass("m2")
      Dim m3 As New MainClass("m3")

      Dim mInfo1 As New MainInfo()
      mInfo1.Name = m1.ToString()
      mInfo1.Methods = m1.GetType().GetMethods(flags).Count
      mInfo1.Properties = m1.GetType().GetProperties(flags).Count

      Dim mInfo3 As New MainInfo()
      mInfo3.Name = m3.ToString()
      mInfo3.Methods = m3.GetType().GetMethods(flags).Count
      mInfo3.Properties = m3.GetType().GetProperties(flags).Count

      Dim attached As New ConditionalWeakTable(Of MainClass, MainInfo)
      Dim value As MainInfo = Nothing

      ' Attach a property to m1 using the Add method, then retrieve it.
      attached.Add(m1, mInfo1)
      If attached.TryGetValue(m1, value) Then
         outputBlock.Text += String.Format("{0}, {1}", m1, value) & vbCrLf
      Else
         outputBlock.Text += String.Format("{0} does not have an attached property.", m1) & vbCrLf
      End If

      ' Attempt to retrieve the value attached to m2.
      value = attached.GetValue(m2, AddressOf Example.CreateAttachedValue)
      If attached.TryGetValue(m2, value) Then
         outputBlock.Text += String.Format("{0}, {1}", m2, value) & vbCrLf
      Else
         outputBlock.Text += String.Format("{0} does not have an attached property.", m2) & vbCrLf
      End If

      ' Atttempt to retrieve the value attached to m3.
      value = attached.GetOrCreateValue(m3)
      outputBlock.Text += String.Format("{0}, {1}", m3, value) & vbCrLf
   End Sub

   Public Function CreateAttachedValue(ByVal m As MainClass) As MainInfo
      Dim info As New MainInfo()
      info.Name = m.ToString()
      info.Methods = m.GetType().GetMethods(flags).Count
      info.Properties = m.GetType().GetProperties(flags).Count
      Return info
   End Function
End Module
' The example displays the following output:
'       m1, m1: 4 Methods, 0 Properties
'       m2, m2: 4 Methods, 0 Properties
'       m3, : 0 Methods, 0 Properties

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

public class MainClass
{
   string Name;

   public MainClass(string name)
   {
      this.Name = name;
   }

   public override string ToString()
   {
      return this.Name;
   }
}

// Define a class to contain information about each Example instance.
public class MainInfo
{
   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 Example
{
   private static BindingFlags flags = BindingFlags.Public | BindingFlags.Instance;

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      MainClass m1 = new MainClass("m1");
      MainClass m2 = new MainClass("m2");
      MainClass m3 = new MainClass("m3");

      MainInfo mInfo1 = new MainInfo();
      mInfo1.Name = m1.ToString();
      mInfo1.Methods = m1.GetType().GetMethods(flags).Length;
      mInfo1.Properties = m1.GetType().GetProperties(flags).Length;

      MainInfo mInfo3 = new MainInfo();
      mInfo3.Name = m3.ToString();
      mInfo3.Methods = m3.GetType().GetMethods(flags).Length;
      mInfo3.Properties = m3.GetType().GetProperties(flags).Length;

      var attached = new ConditionalWeakTable<MainClass, MainInfo>();
      MainInfo value = null;

      // Attach a property to m1 using the Add method, then retrieve it.
      attached.Add(m1, mInfo1);
      if (attached.TryGetValue(m1, out value))
         outputBlock.Text += String.Format("{0}, {1}", m1, value) + "\n";
      else
         outputBlock.Text += String.Format("{0} does not have an attached property.", m1) + "\n";

      // Attempt to retrieve the value attached to m2.
      value = attached.GetValue(m2, Example.CreateAttachedValue);
      if (attached.TryGetValue(m2, out value))
         outputBlock.Text += String.Format("{0}, {1}", m2, value) + "\n";
      else
         outputBlock.Text += String.Format("{0} does not have an attached property.", m2) + "\n";

      // Attempt to retrieve the value attached to m3.
      value = attached.GetOrCreateValue(m3);
      outputBlock.Text += String.Format("{0}, {1}", m3, value) + "\n";
   }

   public static MainInfo CreateAttachedValue(MainClass m)
   {
      MainInfo info = new MainInfo();
      info.Name = m.ToString();
      info.Methods = m.GetType().GetMethods(flags).Length;
      info.Properties = m.GetType().GetProperties(flags).Length;
      return info;
   }
}
// The example displays the following output:
//       m1, m1: 4 Methods, 0 Properties
//       m2, m2: 4 Methods, 0 Properties
//       m3, : 0 Methods, 0 Properties