TryExpression Classe

Definição

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

Herança

Object

Expression

TryExpression

Exemplos

O exemplo a seguir demonstra como criar um TryExpression objeto que contém uma instrução catch usando o TryCatch método.

// 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

Comentários

O bloco do corpo é protegido pelo bloco try.

Os manipuladores consistem em um conjunto de CatchBlock expressões que podem ser instruções catch ou filtros.

O bloco de falha será executado se uma exceção for gerada.

O bloco finalmente é executado independentemente de como o controle sai do corpo.

Somente um dos blocos de falha ou por fim pode ser fornecido.

O tipo de retorno do bloco try deve corresponder ao tipo de retorno de qualquer instrução catch associada.