Expression.IfThen(Expression, Expression) Método

Definição

Namespace:

System.Linq.Expressions

Assembly:

System.Linq.Expressions.dll

Assembly:

System.Core.dll

Assembly:

netstandard.dll

Cria um ConditionalExpression que representa um bloco condicional com uma instrução if.

public:
 static System::Linq::Expressions::ConditionalExpression ^ IfThen(System::Linq::Expressions::Expression ^ test, System::Linq::Expressions::Expression ^ ifTrue);

public static System.Linq.Expressions.ConditionalExpression IfThen (System.Linq.Expressions.Expression test, System.Linq.Expressions.Expression ifTrue);

static member IfThen : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression -> System.Linq.Expressions.ConditionalExpression

Public Shared Function IfThen (test As Expression, ifTrue As Expression) As ConditionalExpression

Parâmetros

test

Expression

Um Expression para definir a propriedade Test igual a ele.

ifTrue

Expression

Um Expression para definir a propriedade IfTrue igual a ele.

Retornos

ConditionalExpression

Um ConditionalExpression que tem a propriedade NodeType igual a Conditional e as propriedades Test e IfTrue definidas como os valores especificados. A propriedade IfFalse foi definida como a expressão padrão e o tipo do ConditionalExpression resultante retornado por esse método é Void.

Exemplos

O exemplo de código a seguir mostra como criar uma expressão que representa um bloco condicional.

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

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

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
Expression.Lambda<Action>(ifThenExpr).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 ifThenExpr As Expression = Expression.IfThen(
     Expression.Constant(test),
     Expression.Call(
         Nothing,
         GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
         Expression.Constant("The condition is true.")
     )
)

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

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