ConditionalWeakTable<TKey, TValue>.Add Method

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Adds a key to the table.

Namespace:  System.Runtime.CompilerServices
Assembly:  mscorlib (in mscorlib.dll)

Syntax

'Declaration
<SecuritySafeCriticalAttribute> _
Public Sub Add ( _
    key As TKey, _
    value As TValue _
)

[SecuritySafeCriticalAttribute]
public void Add(
    TKey key,
    TValue value
)

Parameters

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

• value
  Type: TValue
  The key's property value.

Exceptions

Exception	Condition
ArgumentNullException	key is nulla null reference (Nothing in Visual Basic).
ArgumentException	key already exists.

Remarks

Every key in a ConditionalWeakTable<TKey, TValue> object must be unique. Keys are not unique if they refer to the same object (that is, if passing them as arguments to the Object.ReferenceEquals method returns true).

If the key is garbage-collected during the addition operation, the existing key/value pair is removed and the new key/value pair is added without an exception being thrown.

Examples

The following example defines a MainClass class and a MainInfo class, which provides information about the MainClass instance. The example then calls the Add method to add a MainClass object and its attached MainInfo object to a ConditionalWeakTable<TKey, TValue> table. The example also illustrates calls to the GetOrCreateValue and GetValue methods to add key/value pairs to the table, and to the TryGetValue method to retrieve the value of an existing key.

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

Version Information

Silverlight

Supported in: 5, 4

Permissions

• SecurityCriticalAttribute 

  requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

See Also

Reference

ConditionalWeakTable<TKey, TValue> Class

System.Runtime.CompilerServices Namespace

GetOrCreateValue