Now run the app and you will see login form on the screen. Add data in the fields and save it. Further click next to move to next activity and load data that is saved before. Important Note: The file will only be viewable if you run the App using Android Studio emulator and not in genymotion or any other external alternative emulator. Data should be append every time instead of overriding. And, view report will show all multiple date More than one username and password.
Is there any permission related issue. If yes, please let me know how to change the permission of data folder. Shoot him queries. Follow Author. Leave a Reply Cancel reply Your email address will not be published. Leave this field empty. Exact matches only. The onPostExecute method of this class synchronizes itself again with the main UI thread and allows it to make some updating. This method is called automatically after the doInBackground method finished its work.
To use AsyncTask you must subclass it. Here is the. ProgressValue: Progress is the type of the progress units published during the background computation. ResultValue: ResultValue is the type of the result of the background computation. In Android, AsyncTask is executed and goes through four different steps or method. Here are these four methods of AsyncTasks. This method is mainly used to setup the task for instance by showing a ProgressBar or ProgressDialog in the UI user interface.
Main purpose of this method is to perform the background operations that can take a long time. The parameters of the Asynchronous task are passed to this step for execution. To model the response of the network request, we have our own Result class. The ViewModel triggers the network request when the user taps, for example, on a button:. With the previous code, LoginViewModel is blocking the main thread when making the network request.
We can use the thread pool that we've instantiated to move the execution to a background thread. First, following the principles of dependency injection , LoginRepository takes an instance of Executor as opposed to ExecutorService because it's executing code and not managing threads:. The Executor's execute method takes a Runnable. Let's create another function called makeLoginRequest that moves the execution to the background thread and ignores the response for now:.
Inside the execute method, we create a new Runnable with the block of code we want to execute in the background thread—in our case, the synchronous network request method. Internally, the ExecutorService manages the Runnable and executes it in an available thread.
Any thread in your app can run in parallel to other threads, including the main thread, so you should ensure that your code is thread-safe. Notice that in our example that we avoid writing to variables shared between threads, passing immutable data instead. This is a good practice, because each thread works with its own instance of data, and we avoid the complexity of synchronization.
If you need to share state between threads, you must be careful to manage access from threads using synchronization mechanisms such as locks. This is outside of the scope of this guide. In general you should avoid sharing mutable state between threads whenever possible. In the previous step, we ignored the network request response. To display the result on the screen, LoginViewModel needs to know about it.
We can do that by using callbacks. The function makeLoginRequest should take a callback as a parameter so that it can return a value asynchronously. The callback with the result is called whenever the network request completes or a failure occurs.
In Kotlin, we can use a higher-order function. However, in Java, we have to create a new callback interface to have the same functionality:. The ViewModel needs to implement the callback now. It can perform different logic depending on the result:. In this example, the callback is executed in the calling thread, which is a background thread.
This means that you cannot modify or communicate directly with the UI layer until you switch back to the main thread. You can use a Handler to enqueue an action to be performed on a different thread. To specify the thread on which to run the action, construct the Handler using a Looper for the thread. A Looper is an object that runs the message loop for an associated thread.
Once you've created a Handler , you can then use the post Runnable method to run a block of code in the corresponding thread.
Looper includes a helper function, getMainLooper , which retrieves the Looper of the main thread. You can run code in the main thread by using this Looper to create a Handler. As this is something you might do quite often, you can also save an instance of the Handler in the same place you saved the ExecutorService :.
It's a good practice to inject the handler to the Repository , as it gives you more flexibility. For example, in the future you might want to pass in a different Handler to schedule tasks on a separate thread.
If you're always communicating back to the same thread, you can pass the Handler into the Repository constructor, as shown in the following example.
In this example, the callback passed into the Repository's makeLoginRequest call is executed on the main thread. That means you can directly modify the UI from the callback or use LiveData. You can create a thread pool using one of the Executor helper functions with predefined settings, as shown in the previous example code. 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. For more information about processes and threads in Android, see Process and threads overview.
Content and code samples on this page are subject to the licenses described in the Content License. App Basics. Build your first app. App resources. Resource types. App manifest file. Device compatibility. Multiple APK support. Tablets, large screens, and foldables. Build responsive UIs. Build for foldables.
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