ConditionalWeakTable(Of TKey, TValue).TryGetValue Method (TKey, TValue)
.NET Framework (current version)
Gets the value of the specified key.
Assembly: mscorlib (in mscorlib.dll)
Public Function TryGetValue ( key As TKey, <OutAttribute> ByRef value As TValue ) As Boolean
| Exception | Condition |
|---|---|
| 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(Of 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.
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
SecurityCriticalAttribute
requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.
Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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