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Expression.Condition Method (Expression, Expression, Expression)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Creates a ConditionalExpression that represents a conditional statement.

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

Syntax

'Declaration
Public Shared Function Condition ( _
    test As Expression, _
    ifTrue As Expression, _
    ifFalse As Expression _
) As ConditionalExpression

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

Parameters

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.

Exceptions

Exception Condition
ArgumentNullException

test or ifTrue or ifFalse is nulla null reference (Nothing in Visual Basic).
ArgumentException

test.Type is not Boolean.

-or-

ifTrue.Type is not equal to ifFalse.Type.

Remarks

The Type property of the resulting ConditionalExpression is equal to the Type property of ifTrue.

Examples

The following code example shows how to create an expression that represents a conditional statement. If the first argument evaluates to true, the second argument is executed; otherwise, the third argument is executed.

' Add the following directive to your file:
' Imports System.Linq.Expressions  

Dim num As Integer = 100

' This expression represents a conditional operation; 
' it will evaluate the test (first expression) and
' execute the ifTrue block (second argument) if the test evaluates to true, 
' or the ifFalse block (third argument) if the test evaluates to false.
Dim conditionExpr As Expression = Expression.Condition(
                            Expression.Constant(num > 10),
                            Expression.Constant("n is greater than 10"),
                            Expression.Constant("n is smaller than 10")
                        )

' Print the expression.
outputBlock.Text &= conditionExpr.ToString() & vbCrLf

' The following statement first creates an expression tree,
' then compiles it, and then executes it.       
outputBlock.Text &=
    Expression.Lambda(Of Func(Of String))(conditionExpr).Compile()() & vbCrLf

' This code example produces the following output:
'
' IIF("True", "num is greater than 10", "num is smaller than 10")
' num is greater than 10

// Add the following directive to your file:
// using System.Linq.Expressions; 

int num = 100;

// This expression represents a conditional operation. 
// It evaluates the test (first expression) and
// executes the iftrue block (second argument) if the test evaluates to true, 
// or the iffalse block (third argument) if the test evaluates to false.
Expression conditionExpr = Expression.Condition(
                           Expression.Constant(num > 10),
                           Expression.Constant("num is greater than 10"),
                           Expression.Constant("num is smaller than 10")
                         );

// Print out the expression.
outputBlock.Text += conditionExpr.ToString() + "\n";

// The following statement first creates an expression tree,
// then compiles it, and then executes it.       
outputBlock.Text +=
    Expression.Lambda<Func<string>>(conditionExpr).Compile()() + "\n";

// This code example produces the following output:
//
// IIF("True", "num is greater than 10", "num is smaller than 10")
// num is greater than 10

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.