Handling exceptions

[Sweetiecakes]

Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulating data within the database in question. This class is used
from forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to
show when giving an error message?

Is there any "centralize d" way of handling exceptions: for example,
having a centralized exception handler catch everything, and show an
error message relative to the caught exception?

Thanks

[Bela Istok]

Ok this is a multi answer question because there is no a right way to handle
all the exceptions, one that works for me is:
First if the Exception is an expected exception handle that near the code
that gives the Exception.
Second if you can recover from the exception do it near when it's throwing.
If you don't know or expect the exception and because you are using windows
form you can set a Global exception handler in the application object like
this:
Application.Set UnhandledExcept ionMode(Unhandl edExceptionMode .Automatic);
Application.Thr eadException += new
System.Threadin g.ThreadExcepti onEventHandler( Application_Thr eadException);
static void Application_Thr eadException(ob ject sender,
System.Threadin g.ThreadExcepti onEventArgs e)
{
//Handle here an Unhandled Exception
}

And there you will handle an unexpected exception, but there is a catch, you
need to know if the application can continue after the exception or not.

Regards,

Bela Istok
"Sweetiecak es" <[e-mail] in message
news:48******** *************** @news.fv.fi...

Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulating data within the database in question. This class is used from
forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to show
when giving an error message?

Is there any "centralize d" way of handling exceptions: for example, having
a centralized exception handler catch everything, and show an error
message relative to the caught exception?

Thanks

[Cor Ligthert[MVP]]

SweetieCakes,

A very retro question you ask, I think from about the 70's.

But you can of course make a method that handles those in a kind of general
way and pass the exception.

I don't know if it was just speaking words, but an SQL exception should only
be in design time, because it catches the errors you have made in your
scripts.
Cor

"Sweetiecak es" <[e-mail] ef in bericht
news:48******** *************** @news.fv.fi...

Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulating data within the database in question. This class is used from
forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to show
when giving an error message?

Is there any "centralize d" way of handling exceptions: for example, having
a centralized exception handler catch everything, and show an error
message relative to the caught exception?

Thanks

[Jeroen Mostert]

Cor Ligthert[MVP] wrote:

I don't know if it was just speaking words, but an SQL exception should
only be in design time, because it catches the errors you have made in
your scripts.

I'm in your server room *right now*, unplugging your network. Let's see how
your users like cryptic error messages. :-)

--
J.

[Jon Skeet [C# MVP]]

Cor Ligthert[MVP] <no************ @planet.nlwrote :

A very retro question you ask, I think from about the 70's.

But you can of course make a method that handles those in a kind of general
way and pass the exception.

I don't know if it was just speaking words, but an SQL exception should only
be in design time, because it catches the errors you have made in your
scripts.

And of course nothing *ever* goes wrong with valid SQL... The database
never goes down, there are never concurrency violations, locking
problems, failing to find expected data etc.

There are plenty of reasons why you may see SQL exceptions at execution
time.

--
Jon Skeet - <sk***@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com

[Bela Istok]

Let's not shoot him about this message.

Regards,

Bela Istok
"Cor Ligthert[MVP]" <no************ @planet.nlwrote in message
news:24******** *************** ***********@mic rosoft.com...

SweetieCakes,

A very retro question you ask, I think from about the 70's.

But you can of course make a method that handles those in a kind of
general way and pass the exception.

I don't know if it was just speaking words, but an SQL exception should
only be in design time, because it catches the errors you have made in
your scripts.
Cor

"Sweetiecak es" <[e-mail] ef in bericht
news:48******** *************** @news.fv.fi...

>Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulating data within the database in question. This class is used
from forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to show
when giving an error message?

Is there any "centralize d" way of handling exceptions: for example,
having a centralized exception handler catch everything, and show an
error message relative to the caught exception?

Thanks

[sloan]

Check this entry out:
http://blogs.msdn.com/kcwalina/archi...16/396787.aspx


"Sweetiecak es" <[e-mail] in message
news:48******** *************** @news.fv.fi...

Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulating data within the database in question. This class is used from
forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to show
when giving an error message?

Is there any "centralize d" way of handling exceptions: for example, having
a centralized exception handler catch everything, and show an error
message relative to the caught exception?

Thanks

[Bela Istok]

Nice post sloan, but this is the opposite site of the question. The Cwalina
post talks about throwing exceptions not handling the exceptions. But it's
good to know that too.

Regards,

Bela Istok

"sloan" <sl***@ipass.ne twrote in message
news:OR******** ********@TK2MSF TNGP04.phx.gbl. ..

>>
Check this entry out:
http://blogs.msdn.com/kcwalina/archi...16/396787.aspx


"Sweetiecake s" <[e-mail] in message
news:48******* *************** *@news.fv.fi...

>>Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulatin g data within the database in question. This class is used
from forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to
show when giving an error message?

Is there any "centralize d" way of handling exceptions: for example,
having a centralized exception handler catch everything, and show an
error message relative to the caught exception?

Thanks

[sloan]

Most times, you will write

try
{}
finally
{}

blocks. notice no "catch". You don't catch them.

Then, in your presentation layer, you can catch them.

try
{

}
catch(Exception ex)
{
MessageBox.Show (ex.Message);
//Response.Write( ex.Message); //asp.net

}
There's one more tactic. When you want to catch a dotNet, un-user friendly
exception, and make it into something nicer.

This might be in the BAL layer.

try
{
//try something against the db ........
}
catch ( SqlException sqlex )
{
throw new MyCustomDatabas eIsDownExceptio n( "Sorry, the db is currently not
working" , sqlex );
}
catch (Exception ex)
{
throw new MyCustomNonHand ledException ("Something unexpected happened."
, ex);
}
Its usually a good practice to take the "real" exception and make it the
".InnerExceptio n"...when you create your own exception classes. Which you
can handle with the overloaded constructor.

Most times I don't wrap 'em up for the user nice-like. But that's me.
Depending on the audience and application, you might want to wrap 'em up
nice-like.
............

"Bela Istok" <be****@hotmail .comwrote in message
news:%2******** **********@TK2M SFTNGP06.phx.gb l...

Nice post sloan, but this is the opposite site of the question. The
Cwalina
post talks about throwing exceptions not handling the exceptions. But it's
good to know that too.

Regards,

Bela Istok

>"sloan" <sl***@ipass.ne twrote in message
news:OR******* *********@TK2MS FTNGP04.phx.gbl ...

>>>
Check this entry out:
http://blogs.msdn.com/kcwalina/archi...16/396787.aspx


"Sweetiecakes " <[e-mail] in message
news:48****** *************** **@news.fv.fi.. .
Hello

I'm a bit confused on how one should handle exceptions. I'm currently
building an ADO.NET Windows Forms application. I've built a class for
manipulati ng data within the database in question. This class is used
from forms. Let's assume that there is an SQL error: this will throw an
exception. Where should I handle it? How should I handle it? What to
show when giving an error message?

Is there any "centralize d" way of handling exceptions: for example,
having a centralized exception handler catch everything, and show an
error message relative to the caught exception?

Thanks

[Cor Ligthert[MVP]]

Jon,

And of course nothing *ever* goes wrong with valid SQL... The database
never goes down, there are never concurrency violations, locking
problems, failing to find expected data etc.

As far as I know them will the SQLException ignore all of those problems you
are showing

The SQLexception is needed to check if a stored procedure or an parameter in
that does not exist.
But you are in my opinion a jerk of a developer as you are testing that at
run time.

Cor