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Expression.Label Metodo

Definizione

Crea un oggetto LabelTarget che rappresenta un'etichetta.

Overload

Label()

Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e nessun nome.

Label(LabelTarget)

Crea un oggetto LabelExpression che rappresenta un'etichetta senza un valore predefinito.

Label(String)

Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e il nome specificato.

Label(Type)

Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo specificato.

Label(LabelTarget, Expression)

Crea un oggetto LabelExpression che rappresenta un'etichetta con il valore predefinito specificato.

Label(Type, String)

Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo e il nome specificati.

Label()

Origine:
LabelTarget.cs
Origine:
LabelTarget.cs
Origine:
LabelTarget.cs

Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e nessun nome.

public:
 static System::Linq::Expressions::LabelTarget ^ Label();
public static System.Linq.Expressions.LabelTarget Label ();
static member Label : unit -> System.Linq.Expressions.LabelTarget
Public Shared Function Label () As LabelTarget

Restituisce

Nuovo oggetto LabelTarget.

Esempio

Nell'esempio seguente viene illustrato come creare un'espressione contenente un LabelTarget oggetto .

// Add the following directive to the file:
// using System.Linq.Expressions;

// A label expression of the void type that is the target for Expression.Return().
LabelTarget returnTarget = Expression.Label();

// This block contains a GotoExpression that represents a return statement with no value.
// It transfers execution to a label expression that is initialized with the same LabelTarget as the GotoExpression.
// The types of the GotoExpression, label expression, and LabelTarget must match.
BlockExpression blockExpr =
    Expression.Block(
        Expression.Call(typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }), Expression.Constant("Return")),
        Expression.Return(returnTarget),
        Expression.Call(typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }), Expression.Constant("Other Work")),
        Expression.Label(returnTarget)
    );

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
Expression.Lambda<Action>(blockExpr).Compile()();

// This code example produces the following output:
//
// Return

// "Other Work" is not printed because
// the Return expression transfers execution from Expression.Return(returnTarget)
// to Expression.Label(returnTarget).
' Add the following directive to the file:
' Imports System.Linq.Expressions  

' A label expression of the void type that is the target for Expression.Return().
Dim returnTarget As LabelTarget = Expression.Label()

' This block contains a GotoExpression that represents a return statement with no value.
' It transfers execution to a label expression that is initialized with the same LabelTarget as the GotoExpression.
' The types of the GotoExpression, label expression, and LabelTarget must match.
Dim blockExpr As BlockExpression =
      Expression.Block(
          Expression.Call(GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}), Expression.Constant("Return")),
          Expression.Return(returnTarget),
          Expression.Call(GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}), Expression.Constant("Other Work")),
          Expression.Label(returnTarget)
      )

' The following statement first creates an expression tree,
' then compiles it, and then runs it.
Expression.Lambda(Of Action)(blockExpr).Compile()()

' This code example produces the following output:
'
' Return

' "Other Work" is not printed because 
' the Return expression transfers execution from Return(returnTarget)
' to Expression.Label(returnTarget).

Si applica a

Label(LabelTarget)

Origine:
LabelExpression.cs
Origine:
LabelExpression.cs
Origine:
LabelExpression.cs

Crea un oggetto LabelExpression che rappresenta un'etichetta senza un valore predefinito.

public:
 static System::Linq::Expressions::LabelExpression ^ Label(System::Linq::Expressions::LabelTarget ^ target);
public static System.Linq.Expressions.LabelExpression Label (System.Linq.Expressions.LabelTarget target);
static member Label : System.Linq.Expressions.LabelTarget -> System.Linq.Expressions.LabelExpression
Public Shared Function Label (target As LabelTarget) As LabelExpression

Parametri

target
LabelTarget

Oggetto LabelTarget al quale verrà associato questo oggetto LabelExpression.

Restituisce

Oggetto LabelExpression senza un valore predefinito.

Si applica a

Label(String)

Origine:
LabelTarget.cs
Origine:
LabelTarget.cs
Origine:
LabelTarget.cs

Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e il nome specificato.

public:
 static System::Linq::Expressions::LabelTarget ^ Label(System::String ^ name);
public static System.Linq.Expressions.LabelTarget Label (string name);
public static System.Linq.Expressions.LabelTarget Label (string? name);
static member Label : string -> System.Linq.Expressions.LabelTarget
Public Shared Function Label (name As String) As LabelTarget

Parametri

name
String

Nome dell'etichetta.

Restituisce

Nuovo oggetto LabelTarget.

Si applica a

Label(Type)

Origine:
LabelTarget.cs
Origine:
LabelTarget.cs
Origine:
LabelTarget.cs

Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo specificato.

public:
 static System::Linq::Expressions::LabelTarget ^ Label(Type ^ type);
public static System.Linq.Expressions.LabelTarget Label (Type type);
static member Label : Type -> System.Linq.Expressions.LabelTarget
Public Shared Function Label (type As Type) As LabelTarget

Parametri

type
Type

Tipo di valore passato durante il passaggio all'etichetta.

Restituisce

Nuovo oggetto LabelTarget.

Esempio

Nell'esempio seguente viene illustrato come usare un LabelTarget oggetto in un'espressione ciclo.

// Add the following directive to the file:
// using System.Linq.Expressions;

// Creating a parameter expression.
ParameterExpression value = Expression.Parameter(typeof(int), "value");

// Creating an expression to hold a local variable.
ParameterExpression result = Expression.Parameter(typeof(int), "result");

// Creating a label to jump to from a loop.
LabelTarget label = Expression.Label(typeof(int));

// Creating a method body.
BlockExpression block = Expression.Block(
    new[] { result },
    Expression.Assign(result, Expression.Constant(1)),
        Expression.Loop(
           Expression.IfThenElse(
               Expression.GreaterThan(value, Expression.Constant(1)),
               Expression.MultiplyAssign(result,
                   Expression.PostDecrementAssign(value)),
               Expression.Break(label, result)
           ),
       label
    )
);

// Compile and run an expression tree.
int factorial = Expression.Lambda<Func<int, int>>(block, value).Compile()(5);

Console.WriteLine(factorial);

// This code example produces the following output:
//
// 120
' Add the following directive to the file:
' Imports System.Linq.Expressions  

' Creating a parameter expression.
Dim value As ParameterExpression =
    Expression.Parameter(GetType(Integer), "value")

' Creating an expression to hold a local variable. 
Dim result As ParameterExpression =
    Expression.Parameter(GetType(Integer), "result")

' Creating a label to jump to from a loop.
Dim label As LabelTarget = Expression.Label(GetType(Integer))

' Creating a method body.
Dim block As BlockExpression = Expression.Block(
    New ParameterExpression() {result},
    Expression.Assign(result, Expression.Constant(1)),
    Expression.Loop(
        Expression.IfThenElse(
            Expression.GreaterThan(value, Expression.Constant(1)),
            Expression.MultiplyAssign(result,
                Expression.PostDecrementAssign(value)),
            Expression.Break(label, result)
        ),
        label
    )
)

' Compile an expression tree and return a delegate.
Dim factorial As Integer =
    Expression.Lambda(Of Func(Of Integer, Integer))(block, value).Compile()(5)

Console.WriteLine(factorial)

' This code example produces the following output:
'
' 120

Si applica a

Label(LabelTarget, Expression)

Origine:
LabelExpression.cs
Origine:
LabelExpression.cs
Origine:
LabelExpression.cs

Crea un oggetto LabelExpression che rappresenta un'etichetta con il valore predefinito specificato.

public:
 static System::Linq::Expressions::LabelExpression ^ Label(System::Linq::Expressions::LabelTarget ^ target, System::Linq::Expressions::Expression ^ defaultValue);
public static System.Linq.Expressions.LabelExpression Label (System.Linq.Expressions.LabelTarget target, System.Linq.Expressions.Expression defaultValue);
public static System.Linq.Expressions.LabelExpression Label (System.Linq.Expressions.LabelTarget target, System.Linq.Expressions.Expression? defaultValue);
static member Label : System.Linq.Expressions.LabelTarget * System.Linq.Expressions.Expression -> System.Linq.Expressions.LabelExpression
Public Shared Function Label (target As LabelTarget, defaultValue As Expression) As LabelExpression

Parametri

target
LabelTarget

Oggetto LabelTarget al quale verrà associato questo oggetto LabelExpression.

defaultValue
Expression

Valore di questo oggetto LabelExpression quando l'etichetta viene raggiunta tramite il normale flusso di controllo.

Restituisce

Oggetto LabelExpression con il valore predefinito specificato.

Si applica a

Label(Type, String)

Origine:
LabelTarget.cs
Origine:
LabelTarget.cs
Origine:
LabelTarget.cs

Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo e il nome specificati.

public:
 static System::Linq::Expressions::LabelTarget ^ Label(Type ^ type, System::String ^ name);
public static System.Linq.Expressions.LabelTarget Label (Type type, string name);
public static System.Linq.Expressions.LabelTarget Label (Type type, string? name);
static member Label : Type * string -> System.Linq.Expressions.LabelTarget
Public Shared Function Label (type As Type, name As String) As LabelTarget

Parametri

type
Type

Tipo di valore passato durante il passaggio all'etichetta.

name
String

Nome dell'etichetta.

Restituisce

Nuovo oggetto LabelTarget.

Si applica a