Expression.IfThen(Expression, Expression) Metode

Definisi

Ruang nama:

System.Linq.Expressions

Rakitan:

System.Linq.Expressions.dll

Sumber:

ConditionalExpression.cs

ConditionalExpression Membuat yang mewakili blok bersyarah dengan if pernyataan .

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

Parameter

test

Expression

Untuk Expression mengatur properti yang Test sama dengan.

ifTrue

Expression

Untuk Expression mengatur properti yang IfTrue sama dengan.

Mengembalikan

ConditionalExpression

ConditionalExpression yang memiliki NodeType properti yang sama dengan Conditional dan Testproperti , , IfTruediatur ke nilai yang ditentukan. Properti IfFalse diatur ke ekspresi default dan jenis hasil yang ConditionalExpression dikembalikan oleh metode ini adalah Void.

Contoh

Contoh kode berikut menunjukkan cara membuat ekspresi yang mewakili blok bersyarah.

// 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.