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Expression.IfThenElse Method

Creates a ConditionalExpression that represents a conditional block with if and else statements.

Namespace:  System.Linq.Expressions
Assemblies:   System.Core (in System.Core.dll)
  System.Linq.Expressions (in System.Linq.Expressions.dll)

public static ConditionalExpression IfThenElse(
	Expression test,
	Expression ifTrue,
	Expression ifFalse
)

Parameters

test
Type: System.Linq.Expressions.Expression

An Expression to set the Test property equal to.

ifTrue
Type: System.Linq.Expressions.Expression

An Expression to set the IfTrue property equal to.

ifFalse
Type: System.Linq.Expressions.Expression

An Expression to set the IfFalse property equal to.

Return Value

Type: System.Linq.Expressions.ConditionalExpression
A ConditionalExpression that has the NodeType property equal to Conditional and the Test, IfTrue, and IfFalse properties set to the specified values. The type of the resulting ConditionalExpression returned by this method is Void.

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 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.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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