Could someone provide info about error-handling in wxWidgets or a pointer to documentation?
Specifically, I discovered this behavior: I try to create a wxImage from a file. This is in an event-handler. The file is not present. The call to the image constructor does not throw an exception. (I understand that no wxWidgets code throws exceptions.) A call to image.Ok() returns false. Fine. But after my event-handler exits, wxWidgets gratuitously pops up an error message dialog. That's okay for this particular application, but I wonder how to stop that from happening if I want to handle the error myself. I suspect that the dialog is coming from an event-handler, but I search for things like EVT_ERROR, and came up empty.
There is the class wxLogNull for suppressing those log messages. See http://docs.wxwidgets.org/stable/wx_wxlognull.html#wxlognull where also an example is given.
Read the wxLog overview for more details on how wxWidgets handles this.
You can define your own log target which would throw an exception if an error message is logged. Of course, then you'd probably need to catch it in your event handler anyhow as you probably don't want to just give the user a relatively useless "File couldn't be opened" message but rather a "Image couldn't be opened" one. And if you do this, then why not just test for file.IsOk() directly and use wxLogError() yourself? IOW you can do what you want but I don't really see how is it better than the traditional exception-less way of doing things in this particular case.
Related
I have a function in vb.net that is shared. At one point it throws an error that says an 'open datareader already exists'. But this function is called from several different places in the program. How can I find out which part of the program called the function when it errors out?
You go to the Debug menu, show the Exceptions window, put a tick next to CLR exceptions and then run your program until it errors. As soon as the exception is raised VS will break, you will be able to see the call stack, and find out where the code was before. Note that this causes VS to stop on every exception, handled or not; it can become tedious to get to where you want to be - untick the "always break when this type of exception is thrown" in the exception helper if you just keep getting irrelevant exceptions breaking before this error you're trying to chase
It sounds like you're perhaps not creating/disposing of your DB access resources properly, especially if this is a static/shared context. Are you trying to reuse one DB connection? It wouldn't hurt to post the code of the faulting module
My goal is to influence the error descriptions that appear in BizTalk Administration Console in the Error Information tab of suspended instance windows, after errors occur in my custom functoids. If possible, I would also like the ErrorReport.Description promoted property to display this error description on the failed message.
I've read everything I can find about custom functoid development, but I can't find much about error handling within them. In particular, whenever my functoids throw exceptions, I see the boilerplate "Exception has been thrown at the target of an invocation" message that occurs whenever exceptions occur through reflection, rather than the message on the exception itself.
I had hoped to find something within the BaseFunctoid class framework that would allow me to submit an error string, so as to traverse the reflection boundary. Is there some way to pass error information from within a custom functoid, such that the BizTalk Administration Console will display it?
If I emulate the approach taken by DatabaseLookupFunctoid and DatabaseErrorExtractFunctoid, is there some way I can fail the map with the extracted error, rather than mapping it to a field on the destination schema as is shown in its examples?
The simplest way to do this is using custom C#, writing something like this in your code:
System.Diagnostics.EventLog.WriteEntry("EVENT_LOG_SOURCE", "Error message...", System.Diagnostics.EventLogEntryType.Error);
As Johns-305 mentions, you need to make sure your event source is registered (e.g. System.Diagnostics.EventLog.CreateEventSource("EVENT_LOG_SOURCE", "Application") - but this should really be done as part of your installation steps with an EventLogInstaller or some kind of script to set up the environment). It's certainly true that error handling in BizTalk is just .NET error handling, but one thing to keep in mind is that maps are actually executing as XSLT, and the context in which their executing can have a major impact on how exceptions and errors will be handled, particularly unhandled exceptions.
Orchestrations
If you're executing a transform in an orchestration that has exception handling in it, the exception thrown will be handled and may even fall into additional logging you have in the orchestration - in other words, executing a throw from a C# functiod will work the way you'd think it would work elsewhere in C#. However, I try to avoid this since you never know if a map will at some point be used else where and because exception handling in XSLT doesn't always work the way you'd think (see below).
Send/Receive Ports
Unfortunately, if you're executing a map on a send or receive port and throw an exception within it, you will almost definitely get very unhelpful error message in the event log and a suspended instance in the group hub. There is no easy, straightforward way to simple "cancel" a transform - XSLT 1.0 doesn't have any specified way of doing that (see for example Throwing an exception from XSLT). That leaves you with outputting an error string to a particular node in the output (and/or to the EventLog), or writing lots of completely custom XSLT to try to validate input, or designing your schemas properly and using a validating component where necessary. For example, if you have a node that must match a particular regex, or should never be empty, or should never repeat more than X times, make sure you set those restrictions on the schema and then make sure you pass it through the XmlValidator or similar before attempting to map.
The simplest answer is, you just do.
Keep in mind, there is nothing special at all about error handling in BizTalk apps, it's just regular plain old .Net error handling.
So, what you do is catch the error in you code, write the details to the Windows Event Log (be sure to create a custom Event Source) and...that's it. That is all I do. I don't worry about what appear in BT Admin specifically.strong text
Short and simple:
How to catch pgPL/SQL exceptions with QtSQL?
I haven't found any example or info at the docs.
More details:
I'm developing the front end for a system with Qt 5.3. The database perform some validation at some of the inputs and raise custom exceptions when something is invalid. What I want is to be able to handle these exceptions at he front end code, showing appropriate messages to the user.
EDIT:
I have tried to use the QSqlError class. Although it gave me the exception, it gave me too much data which will need to be parsed to be useful. Is there a way to get the exception raised without parsing the messages?
I am trying to develop a standard when I code applications.
I was curious as to what other developers did when it comes to sql errors or general program errors. Do you output the error to the screen, write to a log file, or something else?
It really depends on the severity of the error.
Is it a show stopper?
Can the software automatically retry and get away with no message?
Can it be ignored?
You can log every exception, or just certain ones, or none. I have a custom Exception class which logs every exception created (of that type).
I have an unhandled exception handler which emails me when there is one.
I'd only send a message to the user when it will change the way the application works from the user's point of view.
Your question is a bit subjective and you would get opinion-based answers if the entire community bothered to answer.
If the error is relevant and important to the user (e.g.: invalid username/password) display it to the user using a message box.
If the error is relevant to the developer, or can be used in the debugging process, use a log or a console output.
The trick is to identify which and how the errors should be displayed to the user. You don't want to bombard the user with exceptions and complicated errors on which the user has no idea on how to act upon.
When I do the try/catch method in my vb.net project I will try the code I want and when it can't do it, i make a message box right after the catch method. The thing is that it will show the message box, and then another message from the program itself. Like for example, I have here a MySQLException, and when i click ok on the message box, it will show another one right after showing the exception itself. How would I be able to get rid of this so the user doesn't have to see this, and the program can continue.
Thanks,
kevin
It sounds like you're actually getting more than one exception. Have you checked the stack traces for both errors?
What I think is happening is that your first function is throwing the MySQLException and then returning nothing. You're then probably getting a NullReferenceException from whatever made the call to the database.
Your best bet is to not catch some many exceptions. Your data layer should be free of Try/Catch blocks unless you're trying to cater for something very specific. Your business layer should then catch any other non-general exceptions that occur specific to the functionality there. Finally, your application layer should be handling all of your general exceptions and reporting on them from there.
Try this. It should only display one message. Make sure your original message is coming from a statement after the Try.
Try
code
Catch ex as exception
call msgbox (ex.message)
end try