The variable 'MyException' is declared but

问题:

I need to clear this warning :

try
{
    doSomething()
}
catch (AmbiguousMatchException MyException)
{
    doSomethingElse()
}

The complier is telling me :

The variable 'MyException' is declared but never used

How can I fix this.

回答1:

1. You can remove it like this:

   try
   {
       doSomething()
   }
   catch (AmbiguousMatchException)
   {
       doSomethingElse()
   }
   

2. Use warning disable like this:

   try
   {
       doSomething()
   }
   #pragma warning disable 0168
   catch (AmbiguousMatchException exception)
   #pragma warning restore 0168
   {
       doSomethingElse()
   }
   

Other familiar warning disable

#pragma warning disable 0168 // variable declared but not used.
#pragma warning disable 0219 // variable assigned but not used.
#pragma warning disable 0414 // private field assigned but not used.

回答2:

You declare a name for the exception, MyException, but you never do anything with it. Since it's not used, the compiler points it out.

You can simply remove the name.

catch(AmbiguousMatchException)
{
   doSomethingElse();
}

回答3:

You can simply write:

catch (AmbiguousMatchException)

and omit the exception name if you won't be using it in the catch clause.

回答4:

The trouble is, you aren't using your variable MyException anywhere. It gets declared, but isn't used. This isn't a problem... just the compiler giving you a hint in case you intended to use it.

回答5:

You could write the exception out to a log if you've got one running. Might be useful for tracking down any problems.

Log.Write("AmbiguousMatchException: {0}", MyException.Message);

回答6:

but never used means that you should use it after catch() such as writing its value to console, then this warning message will disappear.

catch (AmbiguousMatchException MyException)
{
    Console.WriteLine(MyException); // use it here
}