Статья
11/18/2011

Expression.Goto Method (LabelTarget)

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Creates a GotoExpression representing a "go to" statement.

Namespace: System.Linq.Expressions
Assembly: System.Core (in System.Core.dll)

Syntax

'Declaration
Public Shared Function Goto ( _
    target As LabelTarget _
) As GotoExpression

public static GotoExpression Goto(
    LabelTarget target
)

Parameters

target
Type: System.Linq.Expressions.LabelTarget
The LabelTarget that the GotoExpression will jump to.

Return Value

Type: System.Linq.Expressions.GotoExpression
A GotoExpression with Kind equal to Goto, the Target property set to the specified value, and a null value to be passed to the target label upon jumping.

Examples

The following example demonstrates how to create an expression that contains a GotoExpression object.

' Add the following directive to your file:
' Imports System.Linq.Expressions  

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

' This block contains a GotoExpression.
' 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("GoTo")),
          Expression.Goto(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:
'
' GoTo

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

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

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

// This block contains a GotoExpression.
// 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("GoTo")),
        Expression.Goto(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:
//
// GoTo

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

Version Information

Silverlight

Supported in: 5, 4

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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