Expression.Label 方法

定義

命名空間:: System.Linq.Expressions

組件:: System.Core.dll, System.Linq.Expressions.dll

組件:: netstandard.dll, System.Linq.Expressions.dll

組件:: System.Linq.Expressions.dll

組件:: System.Core.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

創造一個 LabelTarget 代表標籤的。

多載

名稱	Description
Label()	建立 LabelTarget 一個代表空值且無名稱的標籤。
Label(LabelTarget)	建立 LabelExpression 一個表示標籤但沒有預設值的。
Label(String)	建立 LabelTarget 一個代表標籤的 void 類型與 given name。
Label(Type)	建立 LabelTarget 一個代表給定類型的標籤的。
Label(LabelTarget, Expression)	建立 LabelExpression 一個代表給定預設值的標籤。
Label(Type, String)	建立 LabelTarget 一個代表標籤的標籤，包含給定型別和名稱。

Label()

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

建立 LabelTarget 一個代表空值且無名稱的標籤。

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

傳回

LabelTarget

新的 LabelTarget.

範例

以下範例示範如何建立包含 LabelTarget 物件的表達式。

// 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).

適用於

Label(LabelTarget)

來源:: LabelExpression.cs

來源:: LabelExpression.cs

來源:: LabelExpression.cs

來源:: LabelExpression.cs

來源:: LabelExpression.cs

建立 LabelExpression 一個表示標籤但沒有預設值的。

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

參數

target: LabelTarget

這將 LabelTarget 與之 LabelExpression 相關聯。

傳回

LabelExpression

LabelExpression A，沒有預設值。

適用於

Label(String)

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

建立 LabelTarget 一個代表標籤的 void 類型與 given name。

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

參數

name: String

標籤的名稱。

傳回

LabelTarget

新的 LabelTarget.

適用於

Label(Type)

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

建立 LabelTarget 一個代表給定類型的標籤的。

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

參數

type: Type

跳轉到標籤時傳遞的值類型。

傳回

LabelTarget

新的 LabelTarget.

範例

以下範例示範如何在迴圈表達式中使用物件 LabelTarget 。

// 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

適用於

Label(LabelTarget, Expression)

來源:: LabelExpression.cs

來源:: LabelExpression.cs

來源:: LabelExpression.cs

來源:: LabelExpression.cs

來源:: LabelExpression.cs

建立 LabelExpression 一個代表給定預設值的標籤。

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

參數

target: LabelTarget

這將 LabelTarget 與之 LabelExpression 相關聯。

defaultValue: Expression

當標籤通過常規控制流程到達時，這個 LabelExpression 值。

傳回

LabelExpression

LabelExpression A 與給定的預設值相符。

適用於

Label(Type, String)

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

來源:: LabelTarget.cs

建立 LabelTarget 一個代表標籤的標籤，包含給定型別和名稱。

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

參數

type: Type

跳轉到標籤時傳遞的值類型。

name: String

標籤的名稱。

傳回

LabelTarget

新的 LabelTarget.

適用於

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