Expression.IfThenElse(Expression, Expression, Expression) 方法

定义

命名空间:
System.Linq.Expressions
程序集:
System.Core.dll, System.Linq.Expressions.dll
程序集:
netstandard.dll, System.Linq.Expressions.dll
程序集:
System.Linq.Expressions.dll
程序集:
System.Core.dll
程序集:
netstandard.dll
Source:
ConditionalExpression.cs
Source:
ConditionalExpression.cs
Source:
ConditionalExpression.cs
Source:
ConditionalExpression.cs
Source:
ConditionalExpression.cs

创建一个 ConditionalExpression 表示带 if 语句的条件块和 else 语句。

public:
 static System::Linq::Expressions::ConditionalExpression ^ IfThenElse(System::Linq::Expressions::Expression ^ test, System::Linq::Expressions::Expression ^ ifTrue, System::Linq::Expressions::Expression ^ ifFalse);
public static System.Linq.Expressions.ConditionalExpression IfThenElse(System.Linq.Expressions.Expression test, System.Linq.Expressions.Expression ifTrue, System.Linq.Expressions.Expression ifFalse);
static member IfThenElse : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression * System.Linq.Expressions.Expression -> System.Linq.Expressions.ConditionalExpression
Public Shared Function IfThenElse (test As Expression, ifTrue As Expression, ifFalse As Expression) As ConditionalExpression

参数

test
Expression

要设置的属性Expression等于的一个Test。

ifTrue
Expression

要设置的属性Expression等于的一个IfTrue。

ifFalse
Expression

要设置的属性Expression等于的一个IfFalse。

返回

ConditionalExpression

一个属性等于和 <a0 /> 的属性，以及设置为指定值的属性。 此方法返回的结果 ConditionalExpression 的类型为 Void。

示例

下面的代码示例演示如何创建表示条件块的表达式。

// Add the following directive to the file:
// using System.Linq.Expressions;
bool test = true;

// This expression represents the conditional block.
Expression ifThenElseExpr = Expression.IfThenElse(
    Expression.Constant(test),
    Expression.Call(
        null,
        typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
        Expression.Constant("The condition is true.")
    ),
    Expression.Call(
        null,
        typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
        Expression.Constant("The condition is false.")
    )
);

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

// This code example produces the following output:
//
// The condition is true.

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

Dim test As Boolean = True

' This expression represents the conditional block.
Dim ifThenElseExpr As Expression = Expression.IfThenElse(
     Expression.Constant(test),
     Expression.Call(
         Nothing,
         GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
         Expression.Constant("The condition is true.")
     ),
     Expression.Call(
         Nothing,
         GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
         Expression.Constant("The condition is false.")
     )
)

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

' This code example produces the following output:
'
' The condition is true.

适用于