vb.net - 在发生异常期间如何在 StreamWriter 之后进行清理？

Question

我正在尝试在发生异常后进行清理，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 somatignBad2 发生，则 sw 已经创建，我需要关闭它。但是我如何知道 sw 是否已创建？

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