Articolo
11/18/2011

ConditionalExpression Class

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

Represents an expression that has a conditional operator.

Inheritance Hierarchy

System.Object
System.Linq.Expressions.Expression
System.Linq.Expressions.ConditionalExpression

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

Syntax

'Declaration
Public Class ConditionalExpression _
    Inherits Expression

public class ConditionalExpression : Expression

The ConditionalExpression type exposes the following members.

Properties

	Name	Description
	CanReduce	Indicates that the node can be reduced to a simpler node. If this returns true, Reduce() can be called to produce the reduced form. (Inherited from Expression.)
	IfFalse	Gets the expression to execute if the test evaluates to false.
	IfTrue	Gets the expression to execute if the test evaluates to true.
	NodeType	Returns the node type of this expression. Extension nodes should return Extension when overriding this method. (Overrides Expression.NodeType.) In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.NodeType. In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.NodeType.
	Test	Gets the test of the conditional operation.
	Type	Gets the static type of the expression that this Expression represents. (Overrides Expression.Type.) In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.Type. In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.Type.

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Methods

	Name	Description
	Accept	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Overrides Expression.Accept(ExpressionVisitor).)
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Reduce	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceAndCheck	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceExtensions	Reduces the expression to a known node type (that is not an Extension node) or just returns the expression if it is already a known type. (Inherited from Expression.)
	ToString	Returns a textual representation of the Expression. (Inherited from Expression.)
	Update	Creates a new expression that is like this one, but using the supplied children. If all of the children are the same, it will return this expression
	VisitChildren	Reduces the node and then calls the visitor delegate on the reduced expression. The method throws an exception if the node is not reducible. (Inherited from Expression.)

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Remarks

Use the Condition factory method to create a ConditionalExpression.

The NodeType of a ConditionalExpression is Conditional.

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.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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