TryExpression 类

定义

public ref class TryExpression sealed : System::Linq::Expressions::Expression

public sealed class TryExpression : System.Linq.Expressions.Expression

type TryExpression = class
    inherit Expression

Public NotInheritable Class TryExpression
Inherits Expression

继承

Object

Expression

TryExpression

示例

以下示例演示如何使用TryExpression该方法创建TryCatch包含 catch 语句的对象。

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

// A TryExpression object that has a Catch statement.
// The return types of the Try block and all Catch blocks must be the same.
TryExpression tryCatchExpr =
    Expression.TryCatch(
        Expression.Block(
            Expression.Throw(Expression.Constant(new DivideByZeroException())),
            Expression.Constant("Try block")
        ),
        Expression.Catch(
            typeof(DivideByZeroException),
            Expression.Constant("Catch block")
        )
    );

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
// If the exception is caught,
// the result of the TryExpression is the last statement
// of the corresponding Catch statement.
Console.WriteLine(Expression.Lambda<Func<string>>(tryCatchExpr).Compile()());

// This code example produces the following output:
//
// Catch block

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

' A TryExpression object that has a Catch statement.
' The return types of the Try block and all Catch blocks must be the same.
Dim tryCatchExpr As TryExpression =
       Expression.TryCatch(
           Expression.Block(
               Expression.Throw(Expression.Constant(New DivideByZeroException())),
               Expression.Constant("Try block")
           ),
           Expression.Catch(
               GetType(DivideByZeroException),
               Expression.Constant("Catch block")
           )
       )

' The following statement first creates an expression tree,
' then compiles it, and then runs it.
' If the exception is caught, 
' the result of the TryExpression is the last statement 
' of the corresponding Catch statement.
Console.WriteLine(Expression.Lambda(Of Func(Of String))(tryCatchExpr).Compile()())

' This code example produces the following output:
'
' Catch block

注解

正文块受 try 块的保护。

处理程序由一组可以是 catch 语句或筛选器的 CatchBlock 表达式组成。

如果引发异常，故障块将运行。

无论控件如何退出正文，最后块都会运行。

只能提供一个故障或最终块。

try 块的返回类型必须与任何关联的 catch 语句的返回类型匹配。