Expression.IfThenElse(Expression, Expression, Expression) Metodo

Definizione

Crea un oggetto ConditionalExpression che rappresenta un blocco condizionale con le istruzioni if e else.

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

Parametri

test
Expression

Oggetto Expression su cui impostare la proprietà Test.

ifTrue
Expression

Oggetto Expression su cui impostare la proprietà IfTrue.

ifFalse
Expression

Oggetto Expression su cui impostare la proprietà IfFalse.

Restituisce

Oggetto ConditionalExpression la cui proprietà NodeType è uguale a Conditional e le cui proprietà Test, IfTrue e IfFalse sono impostate sui valori specificati. Il tipo dell'oggetto ConditionalExpression risultante restituito da questo metodo è Void.

Esempio

Nell'esempio di codice seguente viene illustrato come creare un'espressione che rappresenta un blocco condizionale.

// 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.

Si applica a