In Silverlight, how do I catch an XamlParseException exception - silverlight-4.0

I am running Silverlight 4 with a MVVM framework. From time to time, but not always, during a detail page load, I get a XamlParseException. Since it works 99% of the time, I'm pretty sure the xaml page is fine.
Is it possible to do something similar to the following in my code behind page?
public DetailView() {
try {
InitializeComponent();
} catch (XamlParseException e) {
Debugger.Break();
}
}
In other words, how do I catch the XamlParseException?

You cannot catch this exception using try-catch when the parsing is being handled by the runtime.
The only way to catch this exception is when you are using XamlReader like in this discussion:
http://social.msdn.microsoft.com/Forums/da-DK/wpf/thread/02679567-1bd3-41d1-bfd1-326f646d95d1
You can try handling it on Application_UnhandledException.
More info here: http://msdn.microsoft.com/en-us/library/system.windows.application.unhandledexception(v=vs.95).aspx
And some more info here: http://msdn.microsoft.com/en-us/library/cc189070(v=vs.95).aspx

Related

How to catch exception with action composition in Play 2.3.X

I'm developing an application using Play 2.3.1.
I'm annotating all my controllers with the following Action :
#Override
public Promise<Result> call(final Context ctx) throws Throwable {
try {
return delegate.call(ctx);
} catch (MyCustomException e) {
return handleCustomException(e);
} catch (Exception e) {
return handleUnexpectedError(e);
}
}
The aim of this action is to catch any exception thrown by a controller method in order to send a clean message to the user.
MyCustomException is my application specific exception that extends Exception.
The problem is that even if I throw a MyCustomException in the method of my controller, the corresponding catch statement is never executed.
I always have a RuntimeException caused by my MyCustomException.
The consequence is that no matter what exception occured, the user always sees the result sent by handleUnexpectedError(e).
What am I doing wrong ? Thanks.
After some investigation, the guilty is the Security action of Play.
More details here : https://groups.google.com/forum/#!topic/play-framework/AY4NuQziYyM
Because I added my custom actions at AbstractController level and the #Authenticated(Authenticator.class) annotation at the controller level, the security action composition is the last one to be executed.
Because of the Security.java at line 51, even if my exception is expected, Play throws a RuntimeException.
So the solution is to add the security annotation at method level in order to be sure that it is executed before the first execution of the method.

Exception handling in Controller in ASP.Net MVC 4 with ELMAH and ajax

I've seen a number of posts and articles but am not able to see the solution crisply.
I've installed Elmah.MVC via NuGet and have commented out this line from FilterConfig.cs:
//filters.Add(new HandleErrorAttribute());
So that Elmah would pick up the errors.
It works when I provide an invalid action name and I get a yellow page as well as an email.
I want to know about two other types of errors that my code may generate... how are we supposed to handle them:
1.E.g. if my repository or manager (business logic) layer throws an exception when trying to access database or send an email etc.
a. Is the correct way to NOT implement any kind of try catch in Controllers (or anywhere else for that matter) and let Elmah take care of exceptions?
b. If so, and if it shows a yellow error page, how can we show a view of our own liking?
2.If my view contains ajax calls, e.g. via jqgrid, and behind the scenes there are errors, I've noticed they also get picked up properly by Elmah. But how do I show some kind of an error message to the user as well?
Thanks
Here is what I did:
In controller, I placed try catch:
try
{
//model = getmodelfromdb();
return View("MyView", model);
}
catch (Exception ex)
{
Elmah.ErrorSignal.FromCurrentContext().Raise(ex);
return View("../Error/ShowException", ex);
}
For custom view for 404, I did this in global.asax:
protected void Application_OnError( )
{
var exception = Server.GetLastError( );
Elmah.ErrorSignal.FromCurrentContext().Raise(exception);
Helper.SetSessionValue(SessionKeys.EXCEPTION, exception);
Response.Redirect( "~/Error/ShowException");
}
For jqgrid, I did this in my controller:
[HttpPost]
public ActionResult ListRecords( int page , DateTime? fromdate , DateTime? todate)
{
try
{
var list = FetchListFromDB();
var result = new
{
total = Math.Ceiling(list.Count / (decimal)Helper.PAGE_SIZE),
page = page, //--- current page
records = list.Count, //--- total items
rows = list.List.Select(x => new
{
id = x.EntityID,
cell = new string[]
{
x.Property1,
x.Property2
}
}).ToArray()
};
return Json(result, JsonRequestBehavior.AllowGet);
}
catch (Exception ex)
{
var result = new
{
errorMessage = "An unexpected error occurred while fetching data. An automatic email has been generated for the support team who will address this issue shortly. Details: " + ex.Message,
records = 0
};
Elmah.ErrorSignal.FromCurrentContext().Raise(ex);
return Json(result, JsonRequestBehavior.AllowGet);
}
And this in the View (in the jqgrid definition):
loadComplete:function(data)
{
if (data.errorMessage)
{
alert(data.errorMessage);
}
},
In a general ajax scenario:
success: function(data)
{
if (data.errorMessage)
{
alert(data.errorMessage);
}
else
{
//...
}
},
a. Is the correct way to NOT implement any kind of try catch in Controllers (or anywhere else for that matter) and let Elmah take care of exceptions?
I'd say that Elmah doesn't "take care" of exceptions, it records them. Ideally, you should try to handle the errors - by all means log them, but also add logic to deal with them so that they don't interrupt the user's workflow.
I'd wrap logic in try blocks, and in the catch use
Elmah.ErrorSignal.FromCurrentContext().Raise(exception);
to record anything that goes wrong. Immediately after that line, however, I'd then do something to try to recover from the exception - catch specific exception types, never just catch (Exception e), and deal with them after logging them. The idea is that you should be reviewing your logs, working out what's causing the exceptions, and improving your program so that it doesn't throw exceptions any more.
To show your own error pages, there's the HandleErrorAttribute, or if you don't want to use that there's also the controller's OnException() method, which is called when a controller action method quits with an exception rather than finishing normally. An ExceptionContext object is passed into that method, so you can use that to get the exception that was thrown and log it, do any cleanup that might be required etc.
I know i'm very late to the party but I stumbled upon this answer while searching something similar form Google.
I don't like using try catch blocks everywhere in my code, especially in web apps. I let Elmah catch everything and log it behind the scenes. Then in the web.config file you can redirect based on the error type...
<customErrors mode="RemoteOnly" defaultRedirect="~/Error" >
<error statusCode="500" redirect="~/Error"/>
<error statusCode="404" redirect="~/NotFound"/>
</customErrors>

Silverlight 4 - Exception handling logic reuse when calling WCF proxy

I added a service reference to a silverlight app. When I want to call a method in the service I use those lines :
CustomServiceClient proxy = new CustomServiceClient();
proxy.GetDataCompleted += new EventHandler<GetDataCompletedEventArgs>(Proxy_GetDataCompleted);
try
{
proxy.GetDataAsync(appUser.Id);
proxy.CloseAsync();
}
catch (TimeoutException exception)
{
Console.WriteLine("Got {0}", exception.GetType());
proxy.Abort();
}
catch (CommunicationException exception)
{
Console.WriteLine("Got {0}", exception.GetType());
proxy.Abort();
}
The problem is that every time I need to call a method I am duplicating this code. I can't figure out an elegant way to reuse it (I can use inheritance and make a new class for each method, but it's very ugly).
Sounds like you are looking for something similar to what is described in this CodeProject article.
The answer in this msdn forum post seems to have an elegant solution to this by using extension methods.

Multiple Methods to call a WCF Service

I have a class that handles all the interaction in my application with my WCF service and it seems that MSDN say that the use of Using)_ statement with WCF is bad - I can see why this is bad and agree with it (http://msdn.microsoft.com/en-us/library/aa355056.aspx)
my problem is that their suggested method of implementation will mean that i have 10 methods [as 10 public methods in my service] that will have the same structure code and this of course does not follow the DRY principal - the code looks similar to the following:
try
{
results = _client.MethodCall(input parameteres);
_client.Close();
}
catch (CommunicationException)
{
if (_client != null && _client.State != CommunicationState.Closed)
{
_client.Abort();
}
}
catch (TimeoutException)
{
if (_client != null && _client.State != CommunicationState.Closed)
{
_client.Abort();
}
}
catch (Exception ex)
{
if (_client != null && _client.State != CommunicationState.Closed)
{
_client.Abort();
}
throw;
}
This doesn't have any logging yet but of course when I do come to start logging it then I will have to add the logging work in almost 10 different places
does anyone have any tips on how I can be a bit more resourceful here in reusing code
thanks
paul
I would use some general-purpose, configurable exception handling component that allows basic exception handling processing like logging, re-throwing etc. to be decoupled from the actual place of handling. One example of such a component is Microsoft's Exception Handling Application Block.
Then you could end up with a code like this:
try
{
results = _client.MethodCall(input parameteres);
_client.Close();
}
catch (Exception ex)
{
_client.CloseIfNeeded();
if (!ex.Handle("Wcf.Policy")) throw;
}
where CloseIfNeeded denotes a custom extension method encapsulating the WCF channel closing logic, and the Handle exception method calls the exception handling mechanism, passing in a name of the exception policy that shall be applied on this place.
In most cases, you can reduce exception handling logic to a decent one or two lines of code, giving you several benefits:
instant configurability of exception handling behavior (policies)
extensibility with custom exception handlers bound to specific types of exceptions and exception policies
better manageability and readability of code

Try Catch block

I have the following code
Try
'Some code that causes exception
Catch ex as ExceptionType1
'Handle Section - 1
Catch ex as ExceptionType2
'Handle section - 2
Catch ex as ExceptionType3
'Handle section - 3
Finally
' Clean up
End Try
Suppose ExceptionType1 is thrown by the code which is handled by section - 1. After handling that in section-1, can I have control passed to section-2/section-3? Is that possible?
Change the code to catch all the exceptions in one block and determine the type and execution path from there.
You could call functions in the exception handlers.
Try
'Some code that causes exception'
Catch ex as ExceptionType1
handler_1()
handler_2()
handler_3()
Catch ex as ExceptionType2
handler_2()
handler_3()
Catch ex as ExceptionType3
handler_3()
Finally
handler_4()
End Try
You haven't specified a language, and i don't know the language, so i answer generally.
You can't do that. If you want to have common code, put that either into finally, or if it only needs to be executed for some catching cases, you can copy that code into the respective cases. If the code is bigger and you want to avoid redundancy, you can put it into a function of its own. If that would reduce the readability of your code, you can nest your try/catch blocks (at least in Java and C++. I don't know about your language). Here is an example in Java:
class ThrowingException {
public static void main(String... args) {
try {
try {
throw new RuntimeException();
} catch(RuntimeException e) {
System.out.println("Hi 1, handling RuntimeException..");
throw e;
} finally {
System.out.println("finally 1");
}
} catch(Exception e) {
System.out.println("Hi 2, handling Exception..");
} finally {
System.out.println("finally 2");
}
}
}
This will print out:
Hi 1, handling RuntimeException..
finally 1
Hi 2, handling Exception..
finally 2
put your common code into the outer catch block. Doing it using the nested version also handles cases where an exception occurs without you explicitly re-throwing the old in a catch block. It may fit to what you want even better, but it may also not.
I think you could get the behavior you want if you do nested try blocks. Once an exception is thrown, execution goes to the catch block. If nothing is rethrown, it moves on to finally.