Expression.Condition 方法

定義

命名空間:

System.Linq.Expressions

組件:

System.Linq.Expressions.dll

建立表示條件陳述式的 ConditionalExpression。

多載

Condition(Expression, Expression, Expression)	建立表示條件陳述式的 ConditionalExpression。
Condition(Expression, Expression, Expression, Type)	建立表示條件陳述式的 ConditionalExpression。

Condition(Expression, Expression, Expression)

來源:

ConditionalExpression.cs

建立表示條件陳述式的 ConditionalExpression。

public:
 static System::Linq::Expressions::ConditionalExpression ^ Condition(System::Linq::Expressions::Expression ^ test, System::Linq::Expressions::Expression ^ ifTrue, System::Linq::Expressions::Expression ^ ifFalse);

public static System.Linq.Expressions.ConditionalExpression Condition (System.Linq.Expressions.Expression test, System.Linq.Expressions.Expression ifTrue, System.Linq.Expressions.Expression ifFalse);

static member Condition : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression * System.Linq.Expressions.Expression -> System.Linq.Expressions.ConditionalExpression

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

參數

test

Expression

要將 Expression 屬性設定為與之相等的 Test。

ifTrue

Expression

要將 Expression 屬性設定為與之相等的 IfTrue。

ifFalse

Expression

要將 Expression 屬性設定為與之相等的 IfFalse。

傳回

ConditionalExpression

ConditionalExpression，其 NodeType 屬性等於 Conditional，且 Test、IfTrue 和 IfFalse 屬性設定為指定的值。

例外狀況

ArgumentNullException

test、ifTrue 或 ifFalse 為 null。

ArgumentException

test.Type 不是 Boolean。

-或-

ifTrue.Type 不等於 ifFalse.Type。

範例

下列程式代碼範例示範如何建立代表條件語句的表達式。 如果第一個自變數評估為 true，則會執行第二個自變數，否則會執行第三個自變數。

// 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.
Console.WriteLine(conditionExpr.ToString());

// The following statement first creates an expression tree,
// then compiles it, and then executes it.
Console.WriteLine(
    Expression.Lambda<Func<string>>(conditionExpr).Compile()());

// 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:
' 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.
Console.WriteLine(conditionExpr.ToString())

' The following statement first creates an expression tree,
' then compiles it, and then executes it.       
Console.WriteLine(
    Expression.Lambda(Of Func(Of String))(conditionExpr).Compile()())

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

備註

Type產生的 ConditionalExpression 屬性等於 Type 的ifTrue屬性。

另請參閱

• IfThen(Expression, Expression)
• IfThenElse(Expression, Expression, Expression)

Condition(Expression, Expression, Expression, Type)

來源:

ConditionalExpression.cs

建立表示條件陳述式的 ConditionalExpression。

public:
 static System::Linq::Expressions::ConditionalExpression ^ Condition(System::Linq::Expressions::Expression ^ test, System::Linq::Expressions::Expression ^ ifTrue, System::Linq::Expressions::Expression ^ ifFalse, Type ^ type);

public static System.Linq.Expressions.ConditionalExpression Condition (System.Linq.Expressions.Expression test, System.Linq.Expressions.Expression ifTrue, System.Linq.Expressions.Expression ifFalse, Type type);

static member Condition : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression * System.Linq.Expressions.Expression * Type -> System.Linq.Expressions.ConditionalExpression

Public Shared Function Condition (test As Expression, ifTrue As Expression, ifFalse As Expression, type As Type) As ConditionalExpression

參數

test

Expression

要將 Expression 屬性設定為與之相等的 Test。

ifTrue

Expression

要將 Expression 屬性設定為與之相等的 IfTrue。

ifFalse

Expression

要將 Expression 屬性設定為與之相等的 IfFalse。

type

Type

要將 Type 屬性設定為與之相等的 Type。

傳回

ConditionalExpression

ConditionalExpression，其 NodeType 屬性等於 Conditional，且 Test、IfTrue 和 IfFalse 屬性設定為指定的值。

備註

這個方法允許在 和 ifFalse 表達式的類型不相等的情況下，明確統一條件表達式的結果類型ifTrue。 和 ifFalse 的類型ifTrue都必須隱含參考可指派給結果型別。 允許為 typeVoid。