Expression.SwitchCase 方法

定义

命名空间:

System.Linq.Expressions

程序集:

System.Linq.Expressions.dll

创建要在 SwitchCase 对象中使用的 SwitchExpression 对象。

重载

SwitchCase(Expression, Expression[])	创建在 SwitchCase 中使用的 SwitchExpression。
SwitchCase(Expression, IEnumerable<Expression>)	创建要在 SwitchCase 对象中使用的 SwitchExpression 对象。

SwitchCase(Expression, Expression[])

Source:

SwitchCase.cs

创建在 SwitchCase 中使用的 SwitchExpression。

public:
 static System::Linq::Expressions::SwitchCase ^ SwitchCase(System::Linq::Expressions::Expression ^ body, ... cli::array <System::Linq::Expressions::Expression ^> ^ testValues);

public static System.Linq.Expressions.SwitchCase SwitchCase (System.Linq.Expressions.Expression body, params System.Linq.Expressions.Expression[] testValues);

static member SwitchCase : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression[] -> System.Linq.Expressions.SwitchCase

Public Shared Function SwitchCase (body As Expression, ParamArray testValues As Expression()) As SwitchCase

参数

body

Expression

分支的主体。

testValues

Expression[]

分支的测试值。

返回

SwitchCase

创建的 SwitchCase。

SwitchCase(Expression, IEnumerable<Expression>)

Source:

SwitchCase.cs

创建要在 SwitchCase 对象中使用的 SwitchExpression 对象。

public:
 static System::Linq::Expressions::SwitchCase ^ SwitchCase(System::Linq::Expressions::Expression ^ body, System::Collections::Generic::IEnumerable<System::Linq::Expressions::Expression ^> ^ testValues);

public static System.Linq.Expressions.SwitchCase SwitchCase (System.Linq.Expressions.Expression body, System.Collections.Generic.IEnumerable<System.Linq.Expressions.Expression> testValues);

static member SwitchCase : System.Linq.Expressions.Expression * seq<System.Linq.Expressions.Expression> -> System.Linq.Expressions.SwitchCase

Public Shared Function SwitchCase (body As Expression, testValues As IEnumerable(Of Expression)) As SwitchCase

参数

body

Expression

分支的主体。

testValues

IEnumerable<Expression>

分支的测试值。

返回

SwitchCase

创建的 SwitchCase。

示例

以下示例演示如何创建表示具有默认事例的 switch 语句的表达式。

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

// An expression that represents the switch value.
ConstantExpression switchValue = Expression.Constant(3);

// This expression represents a switch statement
// that has a default case.
SwitchExpression switchExpr =
    Expression.Switch(
        switchValue,
        Expression.Call(
                    null,
                    typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
                    Expression.Constant("Default")
                ),
        new SwitchCase[] {
            Expression.SwitchCase(
                Expression.Call(
                    null,
                    typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
                    Expression.Constant("First")
                ),
                Expression.Constant(1)
            ),
            Expression.SwitchCase(
                Expression.Call(
                    null,
                    typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
                    Expression.Constant("Second")
                ),
                Expression.Constant(2)
            )
        }
    );

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
Expression.Lambda<Action>(switchExpr).Compile()();

// This code example produces the following output:
//
// Default

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

' An expression that represents the switch value.
Dim switchValue As ConstantExpression = Expression.Constant(3)

' This expression represents a switch statement 
' that has a default case.
Dim switchExpr As SwitchExpression =
Expression.Switch(
    switchValue,
    Expression.Call(
                Nothing,
                GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
                Expression.Constant("Default")
            ),
    New SwitchCase() {
        Expression.SwitchCase(
            Expression.Call(
                Nothing,
                GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
                Expression.Constant("First")
            ),
            Expression.Constant(1)
        ),
        Expression.SwitchCase(
            Expression.Call(
                Nothing,
                GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
                Expression.Constant("Second")
            ),
            Expression.Constant(2)
        )
    }
)

' The following statement first creates an expression tree,
' then compiles it, and then runs it.
Expression.Lambda(Of Action)(switchExpr).Compile()()

' This code example produces the following output:
'
' Default

注解

SwitchCase对象中的所有SwitchExpression对象必须具有相同的类型，除非 SwitchExpression 的类型为 void。

每个对象都有 SwitchCase 一个隐式 break 语句，这意味着不存在从一个事例标签到另一个事例标签的隐式下降。