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ConditionalWeakTable<TKey, TValue>.TryGetValue Method

Gets the value of the specified key.

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

public bool TryGetValue(
	TKey key,
	out TValue value
)

Parameters

key
Type: TKey
The key that represents an object with an attached property.
value
Type: TValue%
When this method returns, contains the attached property value. If key is not found, value contains the default value.

Return Value

Type: System.Boolean
true if key is found; otherwise, false.

ExceptionCondition
ArgumentNullException

key is null.

If the key is garbage-collected during this operation, the method may return false and set value to the default value (as if the key were not present).

The following example defines a MainClass class and a MainInfo class, which provides information about the MainClass instance. The example calls the Add, GetOrCreateValue, and GetValue methods to add key/value pairs to a ConditionalWeakTable<TKey, TValue> table. In each case, the example calls the TryGetValue method to confirm that the key/value pair has been added to the table.


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


.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

  • SecurityCriticalAttribute 

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

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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