ConditionalWeakTable<TKey, TValue>.TryGetValue Method
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Gets the value of the specified key.
Namespace: System.Runtime.CompilerServices
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
<SecuritySafeCriticalAttribute> _
Public Function TryGetValue ( _
key As TKey, _
<OutAttribute> ByRef value As TValue _
) As Boolean
[SecuritySafeCriticalAttribute]
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.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | key is nulla null reference (Nothing in Visual Basic). |
Remarks
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).
Examples
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.
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
-
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.