AsyncTask allows you to perform asynchronous work on your user interface. It performs the blocking operations in a worker thread and then publishes the results on the UI thread, without requiring you to handle threads and/or handlers yourself.
To use it, you must subclass AsyncTask and implement the doInBackground() callback method, which runs in a pool of background threads. To update your UI, you should implement onPostExecute(), which delivers the result from doInBackground() and runs in the UI thread, so you can safely update your UI. You can then run the task by calling execute() from the UI thread.
For example, you can implement the previous example using AsyncTask this way:
public void onClick(View v) { new DownloadImageTask().execute("http://example.com/image.png"); } private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> { /** The system calls this to perform work in a worker thread and * delivers it the parameters given to AsyncTask.execute() */ protected Bitmap doInBackground(String... urls) { return loadImageFromNetwork(urls[0]); } /** The system calls this to perform work in the UI thread and delivers * the result from doInBackground() */ protected void onPostExecute(Bitmap result) { mImageView.setImageBitmap(result); } }
Now the UI is safe and the code is simpler, because it separates the work into the part that should be done on a worker thread and the part that should be done on the UI thread.
You should read the AsyncTask reference for a full understanding on how to use this class, but here is a quick overview of how it works:
You can specify the type of the parameters, the progress values, and the final value of the task, using genericsThe method doInBackground() executes automatically on a worker threadonPreExecute(), onPostExecute(), and onProgressUpdate() are all invoked on the UI threadThe value returned by doInBackground() is sent to onPostExecute()You can call publishProgress() at anytime in doInBackground() to execute onProgressUpdate() on the UI threadYou can cancel the task at any time, from any threadCaution: Another problem you might encounter when using a worker thread is unexpected restarts in your activity due to a runtime configuration change (such as when the user changes the screen orientation), which may destroy your worker thread. To see how you can persist your task during one of these restarts and how to properly cancel the task when the activity is destroyed, see the source code for the Shelves sample application.
转载于:https://www.cnblogs.com/sjjg/p/4669778.html
相关资源：AsyncTask官方文档教程整理