ConditionalWeakTable<TKey,TValue>.TryGetValue(TKey, TValue) Método
Definição
Obtém o valor da chave especificada.Gets the value of the specified key.
public:
bool TryGetValue(TKey key, [Runtime::InteropServices::Out] TValue % value);
public bool TryGetValue (TKey key, out TValue value);
member this.TryGetValue : 'Key * 'Value -> bool
Public Function TryGetValue (key As TKey, ByRef value As TValue) As Boolean
Parâmetros
- key
- TKey
A chave que representa um objeto com uma propriedade anexada.The key that represents an object with an attached property.
- value
- TValue
Quando é retornado, este método contém o valor da propriedade anexada.When this method returns, contains the attached property value. Se key não for encontrado, value conterá o valor padrão.If key is not found, value contains the default value.
Retornos
true se key for encontrado; caso contrário, false.true if key is found; otherwise, false.
Exceções
key é null.key is null.
Exemplos
O exemplo a seguir define uma MainClass classe e uma MainInfo classe, que fornece informações sobre a MainClass instância.The following example defines a MainClass class and a MainInfo class, which provides information about the MainClass instance. O exemplo chama os Add GetOrCreateValue métodos, e GetValue para adicionar pares de chave/valor a uma ConditionalWeakTable<TKey,TValue> tabela.The example calls the Add, GetOrCreateValue, and GetValue methods to add key/value pairs to a ConditionalWeakTable<TKey,TValue> table. Em cada caso, o exemplo chama o TryGetValue método para confirmar que o par chave/valor foi adicionado à tabela.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
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
Comentários
Se a chave for coletada por lixo durante essa operação, o método poderá retornar false e definir value como o valor padrão (como se a chave não estivesse presente).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).