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Expression.IfThen Method

Creates a ConditionalExpression that represents a conditional block with an if statement.

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

public static ConditionalExpression IfThen(
	Expression test,
	Expression ifTrue
)

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.

Return Value

Type: System.Linq.Expressions.ConditionalExpression
A ConditionalExpression that has the NodeType property equal to Conditional and the Test, IfTrue, properties set to the specified values. The IfFalse property is set to default expression and 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 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.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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