Question

我正在尝试在异常后进行清理，但我不确定如何处理StreamWriter。

Dim sw As StreamWriter

Try 
    ''// stuff happens

    somethingBad1() ''//Sometimes throws an exception

    sw = New StreamWriter(File.Open("c:\tmp.txt", FileMode.Create))

    ''// stuff happens

    somethingBad2() ''//Also sometimes throws an exception

    sw.Write("Hello World")
    sw.Flush()  ''//Flush buffer
    sw.Close()  ''//Close Stream

Catch ex As Exception
    sw = Nothing       
Finally
    sw = Nothing       
end try

如果somethingBad1抛出异常，我不需要对sw做任何事情;但是，如果发生somathignBad2，则sw已经创建，我需要关闭它。但我如何知道是否已创建sw？

Answer 1

''//stuff happens but you don't care because you didn't instantiate 
''//              StreamWriter yet
somethingBad1() ''//Sometimes throws an exception

Using sw As New StreamWriter("test.dat")
    ''// stuff happens
    somethingBad2() ''//Also sometimes throws an exception
    ''//as you are in a using statement the sw.Dispose method would be called
    ''//which would free the file handle properly
    sw.Write("Hello World")
End Using

Answer 2

仅在分配try变量后（在您的示例中）执行sw。或者使用using声明。

但作为一般规则，您应该关闭StreamWriter（如果不将其与using一起使用），而不是仅为其分配Nothing。此外，应避免捕获所有异常，只处理您知道如何正常处理的异常。

Answer 3

达林说得对，但只有一个风格指向扩展Pavel Minaev的评论：与VB6不同，在VB.Net中设置sw对Nothing的引用没有实际效果。你真的不需要这样做。你可以做的是在你的finally块中有这样的代码：

Finally
    ''# test
    If sw IsNot Nothing Then sw.Dispose()
End

这会照顾所有所需的清理（包括你对catch块的显示）。您甚至不需要在主代码中关闭流。但Using块通常是处理此问题的更好方法。

在异常期间如何在StreamWriter之后清理？

3 个答案: