Whenever I'm running the app in Xcode, I'm running into this issue and I can't really figure out what to do. I'm just trying to fetch all the items in an entity in Core Data, returning a Job array. The only thing I can do if this happens is stop the the app, close it, and open it in the emulator without clicking on the run button.
Here's the image of the code and the error I'm talking about:
Is there anything I can do to fix this? Is this a debug issue or is it a real app problem?
You would use something like this
func generateData(context: NSManagedObjectContext) async throws {
try await context.perform {
//Your fetch code here
}
}
Here is a WWDC video on the subject https://developer.apple.com/wwdc21/10017
The biggest thing I think is not chaining these calls try an condense them, I recently had a client that that was calling perform inside other performs.
async await is all about straight lines you should know exactly what is happening, when it is happening and in what order. There is no hanging on to anything.
Related
I have a finished application which I would like to make available to run on the iOS and Android platforms. I have tested the application as much as possible and it works without problem. But I know there is always the chance that something might go wrong and I could get an exception.
My question is how can I deal with this or what should I do. What happens on the phone, if a Forms application is deployed and there is an exception.
Would appreciate any advice or even links as to how this is handled.
If an exception is thrown and not handled by your code, the app will stop working (i.e. crash).
In order to handle these crashes we are using MS AppCenter (the successor to HockeyApp/Xamarin AppInsights).
You'll have to create a project there (one for each platform), and add the NuGet package to your projects. Afterwards you can initialize it with
AppCenter.Start("ios={Your App Secret};android={Your App Secret}",
typeof(Crashes)); // you'll get the app secrets from appcenter.ms
Crashes will be logged to AppCenter now and you'll be informed whenever there is a new crash.
Please note that it's best practice (if not required by law), that you ask the user for consent before sending the crash report (see here). You are using the delegate Crashes.ShouldAwaitUserConfirmation for that matter. You could for example show an action sheet with Acr.UserDialogs
private bool AwaitUserConfirmation()
{
// you should of course use your own strings
UserDialogs.Instance.ActionSheet(
new ActionSheetConfig
{
Title = "Oopsie",
Message = "The app crashed. Send crash to developers.",
Options = new List<ActionSheetOption>
{
new ActionSheetOption("Sure", () => Crashes.NotifyUserConfirmation(UserConfirmation.Send)),
new ActionSheetOption("Yepp, and don't bug be again.", () => Crashes.NotifyUserConfirmation(UserConfirmation.AlwaysSend)),
new ActionSheetOption("Nope", () => Crashes.NotifyUserConfirmation(UserConfirmation.DontSend))
}
});
return true;
}
await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.High,async () =>
{
await MainPage.bmpsource.SetBitmapAsync(bmp);
});
I putted codes in while loop .When I click button or some controls on running app,the app will crash and pinpoint on code "await MainPage.bmpsource.SetBitmapAsync(bmp);".
VS output:
there will be an exception of type 'System.Threading.Tasks.TaskCanceledException' occurred in System.Private.CoreLib.ni.dll but was not handled in user code
A task was canceled.
Maybe someone can help me,thank you!
You should not use CoreDispatcherPriority.High as that can cause issues (and may be causing this issue).
Please check the link above for more information on this matter.
I have a SignalR hub and two clients (Windows and PCL for Android and iOS). Neither of the clients is able to call some methods on the server. This behaviour is quite odd, since the methods look very similar. Moreover, a colleague of mine is able to call methods I cannot call, and vice versa, does not invoke methods that I invoke with no problems.
Here is an example of a method, which works for me and does not work for my colleague:
public override async Task<bool> RefreshArray(User user, int waitMilis)
{
var cts = new CancellationTokenSource();
try
{
cts.CancelAfter(waitMilis);
await Proxy.Invoke("RefreshArray", user);
return true;
}
catch (Exception ex)
{
OnExceptionOccured(ex);
return false;
}
}
And a method which does not work for me, but works for my colleague:
public override async Task<bool> RequestInformation(User user, Product product, int waitMilis)
{
var cts = new CancellationTokenSource();
try
{
cts.CancelAfter(waitMilis);
await Proxy.Invoke("RequestInformation", user, product);
return true;
}
catch (Exception ex)
{
OnExceptionOccured(ex);
return false;
}
}
Yes, me and my colleague have exactly the same code. And no, there are no typos or different arguments. I have tried to get as much data from the client connection as possible, by setting _connection.TraceLevel = TraceLevels.All; However, I did not get any information on the invoked methods, just on the replies from the hub. When calling RefreshArray, I got exactly the data I requested. When calling RequestInformation, the debugger never even hit the breakpoint in the hub method and the _connection.Trace displayed only this: 11:22:45.6169660 - 7bc57897-489b-49a2-8459-3fcdb8fcf974 - SSE: OnMessage(Data: {})
Has anybody solved a similar issue? Is there a solution?
UPDATE 1
I just realized that I have encountered almost the same issue about a year ago (Possible SignalR bug in Xamarin Android). StackOverflow has also pointed me to a question with almost the same issue (SignalR on Xamarin.iOS - randomly not able to call Hub method), just related to iOS and Azure. However, I got the same proble even outside Xamarin, on Windows Phone 8.1 and and Windows 10 Universal App. Moreover, I am running the server just locally, so it is not an issue od Azure. Is it really possible, that a 2 years old bug has no solution?
UPDATE 2
I have just created a simple console application with SignalR.Client. In the console application every method worked just fine. Amazingly, also the Windows 10 Universal Application started to behave as expected - every hub method was invoked correctly. Windows Phone 8.1 also improved its behaviour (all hub methods invoked). However, every now and then the connection tried to reconnect periodically (for no apparent reason), leading to Connection started reconnecting before invocation result was received. error. The Android application still behaved as before.
So I tried to replicate my previous steps and created another console application, but this time with SignalR.Client.Portable library. To my dissapointment, there was no change in the Android application behaviour.
Next week we will start to test our application on iOS, so I really wonder what new oddities will we encounter.
I have managed to solve the problem (at least so it seems). As it turned out, there is some weird stuff going around, when an application receives an answer from SignalR hub. It seems as if the HubProxy was blocked for a certain period of time on Android, while it drops the connection and starts to reconnect periodically on Windows Phone, not waiting for an asnwer from the hub.
The implementation of RefreshArray on the hub was something like this:
public async Task RefreshArray(User user)
{
await Clients.Caller.SendArray(_globalArray);
await Clients.Caller.SendMoreInformation(_additionalInfo);
}
Because the method sent two methods as an answer, the client Proxy got stuck and each platform handled it in its own unexpected way. The reason why some methods were called on my computer and not on colleagues was, simply, because we had different position of breakpoints, which enabled the application to resolve at least some requests and responses.
The ultimate solution was to add some synchronization into the invokation of methods. Now my hub calls only await Clients.Caller.SendArray(_globalArray);. This is then handled on the client with a ArraySent(string[] array) event, which then subsequently invokes the SendMoreInformation() method on the hub.
Even though NavigationService.CanGoBack returns True, NavigationService.GoBack() throws me these exceptions :
A first chance exception of type 'System.ArgumentException' occurred in System.Windows.dll
A first chance exception of type 'System.Reflection.TargetInvocationException' occurred in
This happens systematically on two case, while the third works fine :
Crashes if I call NavigationService.GoBack() in OnNavigatedTo()
Crashes If I call NavigationService.GoBack() as a result of WebException thrown in my HTTPWebRequest when Internet is not available [1]
Works fine if Internet is available and I call NavigationService.GoBack() when my HTTPWebRequest got results, parsed them, and displayed them.
My theory is that I can't call GoBack() too soon after navigating from a page to another... My question : How can I programatically go back up the navigation stack when an HTTPWebRequest fails to load ?
Edit : I've decided to do it another way, but I think my problems might be due to navigation animations and the Windows Phone C# Toolkit (I use Feb 2011 edition)
[1] Details of my code on case 2 :
I have a simple HTTPWebRequest. My callback does this, and my app crashes when in Airplane Mode. The line NavigationService.GoBack() is responsible, even though NavigationService.CanGoBack returns true.
try
{
response = request.EndGetResponse(result);
}
catch (WebException)
{
Dispatcher.BeginInvoke(() =>
{
NavigationService.GoBack();
});
}
I tried using Deployment.Current.Dispatcher.BeginInvoke() also.
You could try using WebClient client = new WebClient();, then use client.DownloadStringAsync(new Uri("request_url")); to make your request and subscribe to the client.DownloadStringCompleted event to receive your data when the request is completed. After parsing the data, in the event handler you can then call NavigationService.GoBack(); or go to whichever page you want.
Also, if you try to do something in the OnNavigatedTo event and run into trouble you could try using the OnNavigatingFrom instead (on the previous page ofc), cancel the navigation e.Cancel = true;, do your thing as in make the request and stuff, then get the application frame and navigate to e.Uri (basically continuing the navigation you previously cancelled).
Altho this second might represent a solution as well, I think the first one is better as it does all the work async thus not blocking your UI thread. This is what I generally use in my apps. Hope it helps.
I am running several tests with WebDriver and Firefox.
I'm running into a problem with the following command:
WebDriver.get(www.google.com);
With this command, WebDriver blocks till the onload event is fired. While this can normally takes seconds, it can take hours on websites which never finish loading.
What I'd like to do is stop loading the page after a certain timeout, somehow simulating Firefox's stop button.
I first tried execute the following JS code every time that I tried loading a page:
var loadTimeout=setTimeout(\"window.stop();\", 10000);
Unfortunately this doesn't work, probably because :
Because of the order in which scripts are loaded, the stop() method cannot stop the document in which it is contained from loading 1
UPDATE 1: I tried to use SquidProxy in order to add connect and request timeouts, but the problem persisted.
One weird thing that I found today is that one web site that never stopped loading on my machine (FF3.6 - 4.0 and Mac Os 10.6.7) loaded normally on other browsers and/or computers.
UPDATE 2: The problem apparently can be solved by telling Firefox not to load images. hopefully, everything will work after that...
I wish WebDriver had a better Chrome driver in order to use it. Firefox is disappointing me every day!
UPDATE 3: Selenium 2.9 added a new feature to handle cases where the driver appears to hang. This can be used with FirefoxProfile as follows:
FirefoxProfile firefoxProfile = new ProfilesIni().getProfile("web");
firefoxProfile.setPreference("webdriver.load.strategy", "fast");
I'll post whether this works after I try it.
UPDATE 4: at the end none of the above methods worked. I end up "killing" the threads that are taking to long to finish. I am planing to try Ghostdriver which is a Remote WebDriver that uses PhantomJS as back-end. PhantomJS is a headless WebKit scriptable, so i expect not to have the problems of a real browser such as firefox. For people that are not obligate to use firefox(crawling purposes) i will update with the results
UPDATE 5: Time for an update. Using for 5 months the ghostdriver 1.1 instead FirefoxDriver i can say that i am really happy with his performance and stability. I got some cases where we have not the appropriate behaviour but looks like in general ghostdriver is stable enough. So if you need, like me, a browser for crawling/web scraping purposes i recomend you use ghostdriver instead firefox and xvfb which will give you several headaches...
I was able to get around this doing a few things.
First, set a timeout for the webdriver. E.g.,
WebDriver wd;
... initialize wd ...
wd.manage().timeouts().pageLoadTimeout(5000, TimeUnit.MILLISECONDS);
Second, when doing your get, wrap it around a TimeoutException. (I added a UnhandledAlertException catch there just for good measure.) E.g.,
for (int i = 0; i < 10; i++) {
try {
wd.get(url);
break;
} catch (org.openqa.selenium.TimeoutException te) {
((JavascriptExecutor)wd).executeScript("window.stop();");
} catch (UnhandledAlertException uae) {
Alert alert = wd.switchTo().alert();
alert.accept();
}
}
This basically tries to load the page, but if it times out, it forces the page to stop loading via javascript, then tries to get the page again. It might not help in your case, but it definitely helped in mine, particularly when doing a webdriver's getCurrentUrl() command, which can also take too long, have an alert, and require the page to stop loading before you get the url.
I've run into the same problem, and there's no general solution it seems. There is, however, a bug about it in their bug tracking system which you could 'star' to vote for it.
http://code.google.com/p/selenium/issues/detail?id=687
One of the comments on that bug has a workaround which may work for you - Basically, it creates a separate thread which waits for the required time, and then tries to simulate pressing escape in the browser, but that requires the browser window to be frontmost, which may be a problem.
http://code.google.com/p/selenium/issues/detail?id=687#c4
My solution is to use this class:
WebDriverBackedSelenium;
//When creating a new browser:
WebDriver driver = _initBrowser(); //Just returns firefox WebDriver
WebDriverBackedSelenium backedSelenuium =
new WebDriverBackedSelenium(driver,"about:blank");
//This code has to be put where a TimeOut is detected
//I use ExecutorService and Future<?> Object
void onTimeOut()
{
backedSelenuium.runScript("window.stop();");
}
It was a really tedious issue to solve. However, I am wondering why people are complicating it. I just did the following and the problem got resolved (perhaps got supported recently):
driver= webdriver.Firefox()
driver.set_page_load_timeout(5)
driver.get('somewebpage')
It worked for me using Firefox driver (and Chrome driver as well).
One weird thing that i found today is that one web site that never stop loading on my machine (FF3.6 - 4.0 and Mac Os 10.6.7), is stop loading NORMALy in Chrome in my machine and also in another Mac Os and Windows machines of some colleague of mine!
I think the problem is closely related to Firefox bugs. See this blog post for details. Maybe upgrade of FireFox to the latest version will solve your problem. Anyway I wish to see Selenium update that simulates the "stop" button...
Basically I set the browser timeout lower than my selenium hub, and then catch the error. And then stop the browser from loading, then continue the test.
webdriver.manage().timeouts().pageLoadTimeout(55000);
function handleError(err){
console.log(err.stack);
};
return webdriver.get(url).then(null,handleError).then(function () {
return webdriver.executeScript("return window.stop()");
});
Well , the following concept worked with me on Chrome , try the same:
1) Navigate to "about:blank"
2) get element "body"
3) on the elemënt , just Send Keys Ësc
Just in case someone else might be stuck with the same forever loading annoyance, you can use simple add-ons such as Killspinners for Firefox to do the job effortlessly.
Edit : This solution doesn't work if javascript is the problem. Then you could go for a Greasemonkey script such as :
// ==UserScript==
// #name auto kill
// #namespace default
// #description auto kill
// #include *
// #version 1
// #grant none
// ==/UserScript==
function sleep1() {
window.stop();
setTimeout(sleep1, 1500);
}
setTimeout(sleep1, 5000);