How to implement "On Error Resume"?

  • Thread starter Thread starter Rexel
  • Start date Start date
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Rexel

Implementing VB's stock error handler, "On Error Goto Err_Label", is
easy enough using Try/Catch/Finally.

I also figured out how to implement "On Error Resume Next" case, like
when you want to delete a file but don't care about the error if the file
doesn't exists.
So:

Try
'main code

Try
'line causing error
Catch
End Try

'continue main code

Catch
'main error handler
Finally
'cleanup if needed
End Try


The simple Try/Catch block in the middle will do the same as
"On Error Resume Next".

But I haven't been able to implement "On Error Resume", where I
want to try again the line of code that caused the error.
It seems that you have to set up a loop enclosing the Try/Catch block.

How do the experts implement "On Error Resume" case in VB.NET?
 
I can't image why you would do that...
But here some code

dim maxretries as Integer = 5
dim counter as Integer = 0
dim succes as Boolean = False

while (not succes and (counter < maxretries))
try
<do stuff here>
succes = True
catch ...
end try
counter += 1
end while


hope this helps

dominique
 
* Rexel said:
Implementing VB's stock error handler, "On Error Goto Err_Label", is
easy enough using Try/Catch/Finally.

I also figured out how to implement "On Error Resume Next" case, like
when you want to delete a file but don't care about the error if the file
doesn't exists.
So:

Try
'main code

Try
'line causing error
Catch
End Try

'continue main code

Catch
'main error handler
Finally
'cleanup if needed
End Try


The simple Try/Catch block in the middle will do the same as
"On Error Resume Next".

But I haven't been able to implement "On Error Resume", where I
want to try again the line of code that caused the error.
It seems that you have to set up a loop enclosing the Try/Catch block.

How do the experts implement "On Error Resume" case in VB.NET?
Click to expand...

Why not use unstructured error handling in this case? It will make
everything easier...

;-)
 
You can use old school error handling using the Err object or you can use
Structured Exception handling, but you can't mix in the middle of a
structured block. You can rip out the try catch and just use OnError Resume
Next or you can call a goto statement in the catch block. However,
structured exception handling is vastly superior to the old methods and you
should avoid it if at all possible.
 
You can use old school error handling using the Err object or you can use
Structured Exception handling, but you can't mix in the middle of a
structured block. You can rip out the try catch and just use OnError Resume
Next or you can call a goto statement in the catch block. However,
structured exception handling is vastly superior to the old methods and you
should avoid it if at all possible.
Click to expand...

Yes, I would like to use the structured method and avoid the use of On
Error, or Goto etc.
Maybe I didn't make myself clear. I want to implement the functionality
of "On Error Resume", but using only the new structured method.

The reply from Dominique using a loop seems to do the trick.
 
I can't image why you would do that...
But here some code

dim maxretries as Integer = 5
dim counter as Integer = 0
dim succes as Boolean = False

while (not succes and (counter < maxretries))
try
<do stuff here>
succes = True
catch ...
end try
counter += 1
end while


hope this helps

dominique
Click to expand...

Yes, that will do. Thanks. I kind of suspected I had to use a loop.

As to why I would do that, well, in VB we use "On Error Resume" frequently.
One example is when the line causing error is a SQL operation, and the
cause of error is a deadlock. So in this case we try the line agian via On
Error Resume mechanism, after a short delay. Of course there is a counter
for how many trials before giving up.

I am learning VB.NET, and as I go along I try to figure out how to do in
VB.NET the things I used to do in VB, without using any old VB stuff.
 
I'm no "expert" but...

Since I haven't programmed in VB6, I am unsure what it does, but assuming
that it simply retries a particular statement until it finally works.
(Aren't you risking an infinite loop? Seems bad practice.)

dim done as boolean = false
while not done
try
somefunction()
catch ex as system.exception
if ex is the expected one then
'do nothing
else
'handle the error
done = true
end if
end try
end while
 
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