Apologies for the lack of information...
Is there a way to find out what is the specific Exception that is causing a call to throw the Exception?
Currently, I am catching all the Exceptions by doing catch(Exception e) but I know this is not good practices at all.
Is there a way to know from the Exception what is the specific one that caused the issue so I can be more granular?
You can get more information for the particular exception using different methods on it. Here I'm using the System.Diagnostics.Debug class to print in Visual Studio's output console. In your catch block:
using System.Diagnostics;
try
{
// do stuff
}
catch (Exception e)
{
Debug.WriteLine(e.GetType()); // Displays the type of exception
Debug.WriteLine(e.Message()); // Displays the exception message
}
You can see more here: Exception methods &
Exception properties
Option 1 - Documentation
Read the documentation of the method you are calling, if it is a Framework Class type (like SqlConnection.Open) the thrown exceptions are well documented.
Option 2 - Discover them at Run Time
If its a 3rd party library and documentation is limited then check the Exception at runtime using exception.GetType() and then add known exceptions you want to handle as catch blocks.
Personally I prefer to not add catch blocks at all where I am not sure if an Exception will materialize or not. If/When it does the debugger will break (if it is set to break) or you have a global catch all that logs and rethrows. Then you get the type and update your code accordingly. Where you add such a global Exception logger depends on the type of application you are developing. If you go the route of a global logger do take note that you 1) rethrow the Exception so the app breaks at runtime and not swallow it and 2) rethrow using throw; syntax (not throw ex;).
You can catch different types of exceptions. With this solution you are able to handle the different types easily.
try
{
//Try something
}
catch (StackOverflowException soe)
{
//Handle StackOverFlowException
}
catch (FormatException fe)
{
//Handle FormatException
}
//... Other exceptions
If you want to make it more specific for logging errors, try something like:
e.GetType()
Or, if you need some more information like the StackTrace or message:
e.ToString()
If you only want to catch a specific type of exception, you need to do something like:
try {
// someCode
} catch (SpecificExceptionType e) {
// someCode (e.g. Console.WriteLine(e.ToString()); )
}
catch (AnotherSpecificExceptionType e) {
// someCode (e.g. Console.WriteLine(e.ToString()); )
}
Related
I want to be able to get access to e.ErrorDetails contents when an exception occurs in a try/catch block, but unfortunately I can't.
How could I do this without parsing the entire exception object?
try
{...}
catch (Exception e)
{Console.WriteLine(e.ErrorDetails);} //compile error!
Thank you
You need to have an expression of type IScriptEngineException. The simplest approach to that is probably to catch that specific exception. You can't use the interface for that directly, but you can use an exception filter to have the same effect as if you wrote catch (IScriptEngineException ex):
try
{
// ...
}
catch (Exception e) when (e is IScriptEngineException ex)
{
Console.WriteLine(ex.ErrorDetails);
}
// Potentially a more general catch block here
You should consider carefully whether you want to have a more general catch block (catching all exceptions) - without more context, we can't give much advice for that. "Catch all" blocks are generally appropriate only at the top level of a program - e.g. to avoid taking a server down when a single request fails, or to give diagnostic information in a console app before exiting.
I am working in MVC3 Dot Net project Using EF.
We are catching all the Exceptions in an object of Exception (i.e ex)
From this how can I get (or filter) SQlExceptions and I like to show the meaningful message.
facing problem :
I am not getting System.Data.UpdateException class
loop through exception/inner excetion and check if(ex is SQlException) { }
Maybe you missed adding reference to System.Data.Entity so you dont see System.Data.UpdateException class
You shouldn't be catching Exception first (or at all unless you are specifically doing something with all exceptions)
If you want only UpdateExceptions, then you should only catch that exception.
This catch should be above any other handlings that are more generic, for example
try
{
}
catch(System.Data.UpdateException ex)
{
}
catch(Exception ex) //optionally
{
///less generic handling
}
Also consider for general logging ELMAH
http://code.google.com/p/elmah/
is there any way to catch and return an exception thrown from one project to another?
For example, i'm keeping codes in different projects . Say A and B. If A is the engine part and B is the UI part, then an exception occurred in the engine should be caught in UI as well.Please help.
The only reason you'd want to catch the exception in your engine code is if you thought you could handle it, or you needed to do some logging or something like that. There isn't much (any) benefit in catching simply to rethrow. However, assuming you have a valid reason, then in your UI code you can have
try
{
engine.Start();
}
catch (SpecificException se)
{
// Do stuff with specific exception
}
catch (Exception ex)
{
// Show the user something unexpected happened
}
In your Engine code, you can have;
public void Start()
{
try
{
if (this.HasNoOil)
{
throw new SpecificException("Can't go without oil. We'll do some damage");
}
// Other stuff
}
catch (Exception ex)
{
// Log details of exception and throw it up the stack
throw;
}
}
If you want to catch exceptions at the UI level you can not catch them at your engine level.
For the running application there is no difference in which assembly (every project creates an assembly) the exception was thrown.
If you really have to catch and re-throw the exception at your engine level re-throw correctly
catch(Exception ex)
{
// whatever logic
throw;
}
or wrap it
catch(Exception ex)
{
// whatever logic
throw new YourEngineException("Some Message", ex);
}
If you just want to log it, don't do it, if it does not cross process boundaries.
Catch, log, re-throw is an anti pattern in my opinion. It just creates a bazillion log entries, catching at the highest possible level should be enough if you don't destroy the stack trace.
Use wrapping if you can provide extra information to the exception. For Example if you have one method which loads data, changes and saves it you could wrap the exception and add "Error '{0}' when saving" or something else. However don't forget to include the originating exception as inner exception.
In my view it is not possible, until unless these two application share same App domain. To make them part of single app domain you need do remoting or wcF kind of stuff, where you can share the objects between two projects.
Is it correct to catch each exception with Exception class ??? If not then what should be the correct sequence to catch exception within try catch block?
e.g
try{
.
.
some code
.
}
catch(Exception ex)
{
throw ex;
}
No, this is wrong.
Catching only to throw again is pointless.
It's rethrowing incorrectly, which leads to losing the stack trace. The right way to rethrow (when rethrowing makes sense, that is), is simply: throw;
If you want to catch one exception and then throw another, you should keep the first one as an inner exception of the second. This is done by passing it in to the constructor.
Bottom line: Only catch the exceptions that you know what to do with.
If you are throwing the exception right after you catch it -- that is essentially the same as not having a try / catch block at all.
Catch specific exceptions that might occur.
For instance, you try to save a file but for some reason it cannot be written:
try
{
SaveFile();
}
catch(FileIsReadOnlyException)
{
//do whatever to recover
}
catch(Exception ex)
{
//If we hit the generic exception, we're saying that we basically have
//no idea what went wrong, other than the save failed.
//
//Depending on the situation you might want to sink and log it, i.e. do nothing
//but log it so you can debug and figure out what specific exception handler to
//add to your code -- or you might want to try to save to a temporary file and
//exit the program.
//
//If you were UpdatingAnAdvertisement() or doing something else non-critical
//to the functioning of the program, you might just let it continue and
//do nothing.
//
//In that case, you can just omit the generic catch.
}
In my opinion, you should generally try and catch exceptions that you would expect to come out of the code you call in the try block, and let the rest get caught elsewhere. For instance:
try
{
// ... some code that you know may throw ArgumentException or any other known exceptions
}
catch (ArgumentException ex)
{
// ... handle the exception with a good idea of why it was thrown
}
In the catch block, you now can handle the error in a clean, specific way knowing that an invalid argument was passed somewhere in the try block. For example, you could alert the user that they have supplied an invalid argument.
If something happened that you didn't expect (e.g. a NullReferenceException) you probably don't know how to recover from it, so by not catching it you delegate responsibility to the consumer of your component to handle exceptional situations in general.
In short, you should catch exceptions when you know how to handle or correct the error, and allow unknown errors to be caught higher-up the call chain
Make sense?
Always catch most specific exceptions first.
try
{
// some file system code
}
catch (DirectoryNotFoundException e1)
{
// do something about it
}
catch (IOException e2)
{
// do something else about it
}
catch (Exception e)
{
// most generic catch - probably just dump onto screen or error log
}
Rethrowing is made for easier debugging - that is not a way to tell user about the error. The right way to do it:
try
{
// some code that does X
}
catch (Exception e)
{
throw new Exception("describe X and parameters to it where applicable", e);
}
It's not so much that it's incorrect, as that re-throwing the exception is not what you should be doing. There's a host of reasons that re-throwing it is bad mojo and they touch things like maintainability, performance and good coding practices. Unfortunately, the compiler allows it.
As for when you should be catching the exception,a good rule of thumb is that the exception needs to be caught at the point that you want your code to HANDLE the exception.
I am reading C# article.It suggests that
At the end of the catch block, you have three choices:
• Re-throw the same exception, notifying code higher up in the call stack of the
exception.
• Throw a different exception, giving richer exception information to code higher up in
the call stack.
• Let the thread fall out of the bottom of the catch block.
I am unable to understand the points.It would be a great help, if you clarify it by giving simple example.
Thanks in advance.
Update :
When i need to handle rethrown exception ,do i need to have nested try .. catch blocks like
try
{
try
{
}
catch(InvalidOperationException exp)
{
throw;
}
}
catch(Exception ex)
{
// handle the exception thrown by inner catch block
// (in this case the "throw" clause inside the inner "catch")
}
}
Well, here are those different options in code:
Option 1: Rethrow
try
{
// Something
}
catch (IOException e)
{
// Do some logging first
throw;
}
Option 2: Throw a different exception
try
{
// Something
}
catch (IOException e)
{
// Do some logging first
throw new SorryDaveICantDoThatException("Oops", e);
}
Option 3: Let the thread fall out of the bottom
try
{
// Something
}
catch (IOException e)
{
// Possibly do some logging, and handle the problem.
// No need to throw, I've handled it
}
EDIT: To answer the extra question, yes - if you need to handle a rethrown exception, that needs to be handled in an outer scope, exactly as shown in the question. That's very rarely a good idea though. Indeed, catch blocks should relatively rare in the first place, and nested ones even more so.
These are the choices. Difference between 1 and 2 is that if an exception is thrown and you want to debug to the position is it thrown, you will get there with option 1
(all the way down in the try block at the specific object). With option 2 you will and up only at that line (throw new Exception2())
3 is when you want to ignore the exception and just continue
//1
catch (Exception ex)
{
throw;
}
//2
catch (Exception ex)
{
throw new Exception2();
}
//3
catch (Exception ex)
{
}
return something;
In most production systems the last thing you want is a truly unhandled exception. This is why you typically try and catch statements.
You might be wondering why you would want to throw an error you've caught, and here are a few real world examples.
You've caught an exception in a WCF Application, logged the exception, then thrown a faultException instead to be returned to the WCF client. In the same way you might have a traditional asmx, caught an exception, then thrown a SOAP exception back to the client. Point is certain exceptions need to abide by certain rules: a standard .net exception would not be digested well by a WCF client for example.
You've caught an exception somewhere deep inside your code, logged the exception and possibly even taken some action. But higher up in your code you have another routine that is also waiting for exceptions, at this point higher up, an exception could easily change the business workflow. By catching the exception lower down, the code higher up is not aware of any exception, so you need to throw the exception back out to be caught higher up, so that the code you wrote up there can adjust the workflow. Ofc none of this happens by magic, it all has to be coded, and differant programmers use differant techniques.
You might also want to catch an exception around just 1 or a few statements, for example getting a configuration value from an XML file, if something goes wrong, .net might just return object reference not set. You might catch this, then rethrow the exception as "Configuration Value : Customer Name not provided".
Hope this helps.
rethrow the same exception:
try
{
// do something that raises an exception
}
catch (SomeException ex)
{
// do something with ex
throw;
}
throw a different exception
try
{
// do something that raises an exception
}
catch (SomeException ex)
{
// do something with ex
throw new SomeOtherException(ex); // NOTE: please keep ex as an inner exception
}
let the thread fall out:
try
{
// do something that raises an exception
}
catch (SomeException ex)
{
// do something with ex
}
// the code will finish handling the exception and continue on here
1) Re-throw
try
{
...
}
catch (Exception e)
{
...
throw;
}
2) Throw a new exception
try
{
...
}
catch (Exception e)
{
...
throw new NewException("new exception", e);
}
3) Fall out
try
{
...
}
catch (Exception e)
{
...
}
You could also return in the catch block, so there is that 4th option. Return false, return null, etc... (even return a default value.)
Letting the catch block fall through implies that you have successfully dealt with the Exception that was raised in your try block. If you haven't, better rethrow, or fail in some other way.
this isn't c# specific, it's true of any programming language (call them exceptions, call them errors, call them whatever you want).
So, the answer to you question is that this is a basic premise of all programming and you must determine the correct action to take in your code, given the error, the circumstance and the requirements.
Taylor,
As you are learning about Exception handling I would like to add my 2 cents. Exception throwing is very expensive ( expensive being memory hogging of course ) so in this case you should consider assigning the error message to a string and carry it forward through the application to the log or something.
for example:
string errorMessage = string.empty;
try
{
...
}
catch(Exception e)
{
errorMessage = e.Message + e.StackTrace;;
}
This way you can carry this string anyway. This string can be a global property and can be emailed or logged in text file.
I think that there is something to add to the great answers we've already got here.
It may be part of your overall architectural design (or not) but what I've always observed is that you typically only catch where you can add value (or recover from the error) - in other words, not to try...catch...re-throw multiple times for a single operation.
You should normally plan a consistent pattern or design for how you handle exceptions as part of your overall design. You should always plan to handle exceptions in any case, unhandled exceptions are ugly!