Expression.IfThen(Expression, Expression) Метод

Определение

Создает объект ConditionalExpression, представляющий условный блок с оператором if.Creates a ConditionalExpression that represents a conditional block with an if statement.

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

Параметры

test
Expression

Объект Expression, который следует задать в качестве значения свойства Test.An Expression to set the Test property equal to.

ifTrue
Expression

Объект Expression, который следует задать в качестве значения свойства IfTrue.An Expression to set the IfTrue property equal to.

Возвраты

Выражение ConditionalExpression со свойством NodeType, равным Conditional, и свойствами Test и IfTrue, для которых заданы указанные значения.A ConditionalExpression that has the NodeType property equal to Conditional and the Test, IfTrue, properties set to the specified values. Свойству IfFalse присваивается значение выражения по умолчанию, тип получаемого выражения ConditionalExpression, возвращаемого этим методом, — Void.The IfFalse property is set to default expression and the type of the resulting ConditionalExpression returned by this method is Void.

Примеры

В следующем примере кода показано, как создать выражение, представляющее условный блок.The following code example shows how to create an expression that represents a conditional block.

// 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.

Применяется к