How to handle unahandled exceptions in blazor server razor component, In page model, I'm handling with try catch block, but some errors come from razor file and the circuit breaks, application stops. Kindly suggest me the solution to handle this.
I read alot about this issue and what I found that there is no way to make a global error handling right now for blazor, you can handle the error that related with http request like this:
if (!response.IsSuccessStatusCode)
{
var statusCode = response.StatusCode;
switch (statusCode)
{
case HttpStatusCode.NotFound: _navigation.NavigateTo("/Notfound", true);
break;
case HttpStatusCode.Unauthorized: _navigation.NavigateTo("/Error");
break;
default: _navigation.NavigateTo("/Error");
break;
}
throw new ApplicationException($"Reason: {response.ReasonPhrase}");
}
You need also to be carefull about using try catch inside blazor component with some proberty [inject] becuase maybe your blazor circuit will fail!.
You can read more about that in microsoft documents and correct if I am wrong.
Related
I'm writing an app in Xamarin and was wondering if it's possible to externalize my strings I use in exceptions.
For example if I write in my code
throw new Exception("This is an error");
How can I externalize the errormessag "this is an error" ?
I already tried something like this :
throw new Exception("#string/errormessage")
and added errormessage to the Strings.xml file, but that didn't work.
Does anybody know if this can be done?
Assuming this is in your values\Strings.xml:
<string name="stackoverflow">StackOverflow Custom Exception String</string>
You can use it as your custom exception message via:
button.Click += delegate {
throw new Exception(this.Resources.GetString(Resource.String.stackoverflow));
};
I have a service method which does some operation inside a transaction.
public User method1() {
// some code...
Vehicle.withTransaction { status ->
// some collection loop
// some other delete
vehicle.delete(failOnError:true)
}
if (checkSomething outside transaction) {
return throw some user defined exception
}
return user
}
If there is a runtime exception we dont have to catch that exception and the transaction will be rolled back automatically. But how to determine that transaction rolled back due to some exception and I want to throw some user friendly error message. delete() call also wont return anything.
If I add try/catch block inside the transaction by catching the Exception (super class) it is not getting into that exception block. But i was expecting it to go into that block and throw user friendly exception.
EDIT 1: Is it a good idea to add try/catch arround withTransaction
Any idea how to solver this?? Thanks in advance.
If I understand you question correctly, you want to know how to catch an exception, determine what the exception is, and return a message to the user. There are a few ways to do this. I will show you how I do it.
Before I get to the code there are a few things I might suggest. First, you don't need to explicitly declare the transaction in a service (I'm using v2.2.5). Services are transactional by default (not a big deal).
Second, the transaction will automatically roll back if any exception occurs while executing the service method.
Third, I would recommend removing failOnError:true from save() (I don't think it works on delete()... I may be wrong?). I find it is easier to run validate() or save() in the service then return the model instance to the controller where the objects errors can be used in a flash message.
The following is a sample of how I like to handle exceptions and saves using a service method and try/catch in the controller:
class FooService {
def saveFoo(Foo fooInstance) {
return fooInstance.save()
}
def anotherSaveFoo(Foo fooInstance) {
if(fooInstance.validate()){
fooInstance.save()
}else{
do something else or
throw new CustomException()
}
return fooInstance
}
}
class FooController {
def save = {
def newFoo = new Foo(params)
try{
returnedFoo = fooService.saveFoo(newFoo)
}catch(CustomException | Exception e){
flash.warning = [message(code: 'foo.validation.error.message',
args: [org.apache.commons.lang.exception.ExceptionUtils.getRootCauseMessage(e)],
default: "The foo changes did not pass validation.<br/>{0}")]
redirect('to where ever you need to go')
return
}
if(returnedFoo.hasErrors()){
def fooErrors = returnedFoo.errors.getAllErrors()
flash.warning = [message(code: 'foo.validation.error.message',
args: [fooErrors],
default: "The foo changes did not pass validation.<br/>${fooErrors}")]
redirect('to where ever you need to go')
return
}else {
flash.success = [message(code: 'foo.saved.successfully.message',
default: "The foo was saved successfully")]
redirect('to where ever you need to go')
}
}
}
Hope this helps, or gets some other input from more experienced Grails developers.
Here are a few other ways I've found to get exception info to pass along to your user:
request.exception.cause
request.exception.cause.message
response.status
A few links to other relevant questions that may help:
Exception handling in Grails controllers
Exception handling in Grails controllers with ExceptionMapper in Grails 2.2.4 best practice
https://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/exception/ExceptionUtils.html
We've noticed a couple of times in our mobile applications that users have reported the application hanging or seeming to become unresponsive between views / rare crashes when switching between views. We've tracked down these cases to when our view model constructors throw uncaught exceptions.
We want to put a solution in place so that if a view model fails to construct for some reason then we can notify the user and provide some message that will be useful to us when it's logged through support.
I've been taking a look at doing this but haven't found a reliable way to achieve this.
The first thing we tried was at the IMvxViewModelLocator level. We already have a custom implementation of IMvxViewModelLocator so we've modified this. We allow all exceptions to be thrown and then we have an IErrorHandler interface which each platform implements. We then call this to attempt to show a dialog. This has proved to be unreliable and the dialog does not always display. Something along the lines of: (note - here ResolveViewModel will always return true or throw)
public override bool TryLoad(Type viewModelType, IMvxBundle parameterValues, IMvxBundle savedState, out IMvxViewModel viewModel)
{
try
{
return ResolveViewModel(viewModelType, parameterValues, savedState, out viewModel);
}
catch (Exception exception)
{
_errorHandler.HandleViewModelConstructionException(viewModelType, exception);
viewModel = null;
return false;
}
}
What we would ideally like to do is intercept any failure to construct a view model and then re-request an ErrorViewModel. We've tried to do this 2 ways:
1)
We've tried defining a custom IMvxViewDispatcher for each platform and we're trying to intercept failures as below but if an exception in the constructor is thrown we never get back this far:
public class TouchDispatcher : MvxTouchUIThreadDispatcher, IMvxViewDispatcher
{
private readonly IMvxTouchViewPresenter _presenter;
public TouchDispatcher(IMvxTouchViewPresenter presenter)
{
_presenter = presenter;
}
public bool ShowViewModel(MvxViewModelRequest request)
{
Action action = () =>
{
_presenter.Show(request);
};
try
{
bool success = RequestMainThreadAction(action);
return !success ? HandleError() : success;
}
catch (Exception)
{
return HandleError();
}
}
// Other bits
}
2)
We thought we might have more success at the presenter level. We modified our ViewPresenter for each platform and we have overridden void Show(MvxViewModelRequest request). This has not proved to be successful either as exceptions don't propagate back this far.
This leaves me thinking that maybe we are better attempting this at the IMvxViewModelLocator level again.
Has anyone found a way to reliably intercept failures to construct view models and then ideally re-request a different view model / present some dialog to the user?
It seems you've identified that the core of the problem is when: "view model constructors throw uncaught exceptions."
This is going to be slightly problematic as the ViewModel's are generally constructed during View lifecycle overrides like ViewDidLoad, OnCreate or NavigatedTo - which is generally after the Presenter has finished requesting presentation.
As you've already found an easy place to identify when ViewModel construction has failed is in a custom IMvxViewModelLocator - others likeIMvxViewModelLoader are also possible. This is probably the easiest place to catch the error and to trigger the error handling - you can then get hold of the IMvxViewDispatcher (or presenter) there in order to change the display. However, you will still need to make sure your Views can handle null created ViewModels - as the ViewDidLoad, etc calls will still need to complete.
I tried using special variable $message described here http://www.symfony-project.org/cookbook/1_2/en/error_templates but it seems this variable isn't defined in symfony 1.4, at least it doesn't contain message passed to exception this way throw new sfException('some message')
Do you know other way to pass this message to error.html.php ?
You'll need to do some custom error handling. We implemented a forward to a custom symfony action ourselves. Be cautious though, this action itself could be triggering an exception too, you need to take that into account.
The following might be a good start. First add a listener for the event, a good place would be ProjectConfiguration.class.php:
$this->dispatcher->connect('application.throw_exception', array('MyClass', 'handleException'));
Using the event handler might suffice for what you want to do with the exception, for example if you just want to mail a stack trace to the admin. We wanted to forward to a custom action to display and process a feedback form. Our event handler looked something like this:
class MyClass {
public static function handleException(sfEvent $event) {
$moduleName = sfConfig::get('sf_error_500_module', 'error');
$actionName = sfConfig::get('sf_error_500_action', 'error500');
sfContext::getInstance()->getRequest()->addRequestParameters(array('exception' => $event->getSubject()));
$event->setReturnValue(true);
sfContext::getInstance()->getController()->forward($moduleName, $actionName);
}
}
You can now configure the module and action to forward to on an exception in settings.yml
all:
.actions:
error_500_module: error
error_500_action: error500
In the action itself you can now do whatever you want with the exception, eg. display the feedback form to contact the administrator. You can get the exception itself by using $request->getParameter('exception')
I think I found a much simpler answer. On Symfony 1.4 $message is indeed not defined, but $exception is (it contains the exception object).
So just echo $exception->message.
Et voilà!
I've found another trick to do that - sfContext can be used to pass exception message to error.html.php but custom function have to be used to throw exception. For example:
class myToolkit {
public static function throwException($message)
{
sfContext::getInstance()->set('error_msg', $message);
throw new sfException($message);
}
than insted of using throw new sfException('some message') you should use myToolkit::throwException('some message')
To display message in error.html.php use <?php echo sfContext::getInstance()->get('error_msg') ?>
I'm trying to leverage the using block more and more these days when I have an object that implements IDisposable but one thing I have not figured out is how to catch an exception as I would in a normal try/catch/finally ... any code samples to point me in the right direction?
Edit: The question was modified after reading through the replies. It was "How to Throw an exception in a using block with .NET 2.0?" but I was actually looking for a way to catch these exceptions inside a using block.
I'm looking for more detail on rolling my own catching block inside a using block.
Edit: What I wanted to avoid is having to use a try/catch/finally inside my using block like #Blair showed. But maybe this is a non issue...
Edit: #Blair, this is exactly what I was looking for, thanks for the detailed reply!
I don't really understand the question - you throw an exception as you normally would.
If MyThing implements IDisposable, then:
using ( MyThing thing = new MyThing() )
{
...
throw new ApplicationException("oops");
}
And thing.Dispose will be called as you leave the block, as the exception's thrown. If you want to combine a try/catch/finally and a using, you can either nest them:
try
{
...
using ( MyThing thing = new MyThing() )
{
...
}
...
}
catch ( Exception e )
{
....
}
finally
{
....
}
(Or put the try/catch/finally in the using):
using ( MyThing thing = new MyThing() )
{
...
try
{
...
}
catch ( Exception e )
{
....
}
finally
{
....
}
...
} // thing.Dispose is called now
Or you can unroll the using and explicitly call Dispose in the finally block as #Quarrelsome demonstrated, adding any extra exception-handling or -recovery code that you need in the finally (or in the catch).
EDIT: In response to #Toran Billups, if you need to process exceptions aside from ensuring that your Dispose method is called, you'll either have to use a using and try/catch/finally or unroll the using - I don't thinks there's any other way to accomplish what you want.
Yeah there is nothing different about throwing exceptions in using blocks.
Remember that the using block basically translates to:
IDisposable disposable = null;
try
{
disposable = new WhateverYouWantedToMake();
}
finally
{
disposable.Dispose()
}
So you will have to roll your own catching if you want to catch anything but catching/throwing is a completely separate concern from the using. The finally is almost guaranteed to execute (save an uncatchable exception (e.g. stackoverflow or outofmemory) or someone pulling the power out of the PC).
You need to have a try statement to catch an exception
Either you can use an try statement within the using block or you can use a using block in a try block
But you need to use a try block to catch any exceptions occuring