Let's dissect the coroutines code in the login function:. Since this coroutine is started with viewModelScope , it is executed in the scope of the ViewModel. If the ViewModel is destroyed because the user is navigating away from the screen, viewModelScope is automatically cancelled, and all running coroutines are canceled as well.
One issue with the previous example is that anything calling makeLoginRequest needs to remember to explicitly move the execution off the main thread. Let's see how we can modify the Repository to solve this problem for us. We consider a function main-safe when it doesn't block UI updates on the main thread. Use the withContext function from the coroutines library to move the execution of a coroutine to a different thread:.
This keyword is Kotlin's way to enforce a function to be called from within a coroutine. In the following example, the coroutine is created in the LoginViewModel. As makeLoginRequest moves the execution off the main thread, the coroutine in the login function can be now executed in the main thread:.
Note that the coroutine is still needed here, since makeLoginRequest is a suspend function, and all suspend functions must be executed in a coroutine. This code differs from the previous login example in a couple of ways:. To handle exceptions that the Repository layer can throw, use Kotlin's built-in support for exceptions. In the following example, we use a try-catch block:. In this example, any unexpected exception thrown by the makeLoginRequest call is handled as an error in the UI.
For a more detailed look at coroutines on Android, see Improve app performance with Kotlin coroutines. Content and code samples on this page are subject to the licenses described in the Content License. How can I fix 'android. Ask Question. Asked 10 years, 5 months ago. Active 4 months ago.
Viewed 1. I got an error while running my Android project for RssReader. Peter Mortensen It explains why this occurs on Android 3. To be on rite track first read about the Network Requests in android then i would recommend to study "Volley". There are many alternative libraries that solve this issue. Many are listed at the bottom of this page. If you got more, we take them : — Snicolas. You need to run internet activities on a thread separate from main UI thread — Naveed Ahmad.
Android 7. Apps that exhibit this behavior now throw an android. Add a comment. Active Oldest Votes. AsyncTask Android Developers This exception is thrown when an application attempts to perform a networking operation on its main thread. Shayan Shafiq 1, 5 5 gold badges 17 17 silver badges 24 24 bronze badges. Michael Spector Michael Spector So this running network operations on main thread is only problematic in android not in standard java code code written in java but not for android application.??
This is a good solution and it saved my time! Add: StrictMode. Wow thanks for that explanation I now understand. I saw an app and it had implemented that ThreadPolicy in its java classes I was abit confused what it was doing.
When network was low I was seeing the Consequence which you're talking about. I solved this problem using a new Thread. V-rund Puro-hit 5, 9 9 gold badges 29 29 silver badges 50 50 bronze badges. Luiji Dr. Luiji 5, 1 1 gold badge 13 13 silver badges 11 11 bronze badges. How woulod you pass paramaters to this?
If you need to access the UI after the request, you need to return to the main thread at the end as explained here. Some of the down-sides include: AsyncTask's created as non-static inner classes have an implicit reference to the enclosing Activity object, its context, and the entire View hierarchy created by that activity.
This reference prevents the Activity from being garbage collected until the AsyncTask's background work completes. AsyncTask has different execution characteristics depending on the platform it executes on: prior to API level 4 AsyncTasks execute serially on a single background thread; from API level 4 through API level 10, AsyncTasks execute on a pool of up to threads; from API level 11 onwards AsyncTask executes serially on a single background thread unless you use the overloaded executeOnExecutor method and supply an alternative executor.
Code that works fine when running serially on ICS may break when executed concurrently on Gingerbread, say if you have inadvertent order-of-execution dependencies. If you want to avoid short-term memory leaks, have well-defined execution characteristics across all platforms, and have a base to build really robust network handling, you might want to consider: Using a library that does a nice job of this for you - there's a nice comparison of networking libs in this question , or Using a Service or IntentService instead, perhaps with a PendingIntent to return the result via the Activity's onActivityResult method.
IntentService approach Downsides: More code and complexity than AsyncTask , though not as much as you might think Will queue requests and run them on a single background thread. You can easily control this by replacing IntentService with an equivalent Service implementation, perhaps like this one.
Um, I can't think of any others right now actually Upsides: Avoids the short-term memory leak problem If your activity restarts while network operations are in-flight it can still receive the result of the download via its onActivityResult method A better platform than AsyncTask to build and reuse robust networking code.
Example: if you need to do an important upload, you could do it from AsyncTask in an Activity , but if the user context-switches out of the app to take a phone call, the system may kill the app before the upload completes.
It is less likely to kill an application with an active Service. If you use your own concurrent version of IntentService like the one I linked above you can control the level of concurrency via the Executor. Implementation summary You can implement an IntentService to perform downloads on a single background thread quite easily.
You can tell it what to download via Intent extras, and pass it a PendingIntent to use to return the result to the Activity : import android. IntentService; import android.
PendingIntent; import android. Intent; import android. Log; import java. InputStream; import java. MalformedURLException; import java. Stevie Stevie 7, 3 3 gold badges 28 28 silver badges 29 29 bronze badges. Mark Allison Mark Allison There are two solutions of this problem.
Don't use a network call in the main UI thread. Use an async task for that. Dipak Keshariya Dipak Keshariya Following your second solution is a bad practice. Async is the way to do it correctly. You are like hiding your problem if you change the policy! Do the network actions on another thread. Community Bot 1 1 1 silver badge. Perhaps worth stressing the point that if you use a Service you will still need to create a separate thread - Service callbacks run on the main thread.
An IntentService, on the other hand, runs its onHandleIntent method on a background thread. Guidelines specify 2 to 3 seconds max. You disable the strict mode using following code: if android. Yes ANR error would be come. This is a really bad answer. You should not change the thread's policy but to write better code: do not make network operations on main thread!
Sandeep You and other viewers should read this too. Dhruv Jindal Dhruv Jindal 1, 10 10 silver badges 17 17 bronze badges. Anonymous Runnable is NOT the best way, since it has an implicit reference to the enclosing class and preventing it from being GC ed until the thread completes!
Vaishali Sutariya Vaishali Sutariya 5, 28 28 silver badges 32 32 bronze badges. Oleksiy Oleksiy Gavriel it creates duplicates of everything you annotate, whether it's a method, activity, fragment, singleton etc, so there is twice as much code and it takes longer to compile it. It may also have some issues due to bugs in the library. Alternatively, if you want to customize the details of the thread pool, you can create an instance using ThreadPoolExecutor directly. You can configure the following details:.
Here's an example that specifies thread pool size based on the total number of processor cores, a keep alive time of one second, and an input queue. It's important to understand the basics of threading and its underlying mechanisms.
There are, however, many popular libraries that offer higher-level abstractions over these concepts and ready-to-use utilities for passing data between threads. In practice, you should pick the one that works best for your app and your development team, though the rules of threading remain the same.
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