Expression.IfThen Method (Expression, Expression)

 

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

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

Public Shared Function IfThen (
	test As Expression,
	ifTrue As Expression
) As ConditionalExpression

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:
' 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.

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
Return to top
Show: