嵌套的尝试/捕捉块是一个坏主意吗？

假设我们有这样一个结构:

Try
' Outer try code, that can fail with more generic conditions,
' that I know less about and might not be able to handle


Try
' Inner try code, that can fail with more specific conditions,
' that I probably know more about, and are likely to handle appropriately
Catch innerEx as Exception
' Handle the inner exception
End Try


Catch outerEx as Exception
' Handle outer exception
End Try

我已经看到了一些意见，嵌套像这样的 Try块是不鼓励的，但我不能找到任何具体的原因。

这是坏代码吗? 如果是，为什么？

90905

小开

最佳答案

There are certain circumstances where they're a good idea, e.g. one try/catch for the whole method and another inside a loop as you want to handle the exception and continue processing the rest of a collection.

Really the only reason to do it is if you want to skip the bit that errored and carry on, instead of unwinding the stack and losing context. Opening multiple files in an editor is one example.

That said, exceptions should (as the name implies) be exceptional. A program should handle them but try to avoid them as part of normal execution flow. They're computationally expensive in most languages (Python being one notable exception).

One other technique which can be useful is catching specific exception types...

Try
'Some code to read from a file


Catch ex as IOException
'Handle file access issues (possibly silently depending on usage)
Catch ex as Exception
' Handle all other exceptions.
' If you've got a handler further up, just omit this Catch and let the
' exception propagate
Throw
End Try

We also use nested try/catches in our error handling routines...

    Try
Dim Message = String.Format("...", )
Try
'Log to database
Catch ex As Exception
'Do nothing
End Try


Try
'Log to file
Catch ex As Exception
'Do nothing
End Try
Catch ex As Exception
'Give up and go home
End Try