Android Studio - Complete Android Apps Tutorial - Thread and Async Task - Day 13 - 9.34

Thread and AsyncTask
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 Why Another Thread?  Failure to return from an Activity callback method within a few seconds 5 secs will cause Android to think your application is stuck  Pops an error dialog ANR  Kills your activity  Even delays shorter than a few seconds will let user feels that the application is unresponsive/slow/lag
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 Handler  Only the main thread/UI thread can update the UI, other threads updating the UI will cause CalledFromWrongThreadException  If background thread needs to update the UI, request the UI thread to do the update via a Handler  Construct a Handler in the main thread Handler mHandler = new Handler;
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 Why Another Thread?  Possible reasons:  Connecting to Internet to fetch data XML/JSON  Since API Level 11, this will cause NetworkOnMainThreadException  Reading or writing to a removable storage  Many SQLite database operations  Lengthy mathematical computations involving many loops
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 Application Not Responding ANR dialog
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 Solved using  Thread & Runnable  java.lang.Thread  java.lang.Runnable  Suitable for infinite loop  AsyncTask  android.os.AsyncTask  Suitable for task that will be completed in a finite duration
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 Monitoring Threads  Via Android Device Monitor
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 Thread  Construct a new Thread  Override run in the Thread and the task in run will be run in another thread  Start the thread with start new Thread public void run // background task ; .start;
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 Handler  Only the main thread/UI thread can update the UI, other threads updating the UI will cause CalledFromWrongThreadException  If background thread needs to update the UI, request the UI thread to do the update via a Handler  Construct a Handler in the main thread Handler mHandler = new Handler;
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 Handler.post  Puts a Runnable on the message queue  Will get processed once other messages already on the queue are processed mHandler.postnew Runnable @Override public void run // update UI in main thread ;
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 Handler.postDelayed  Like post, except a minimum delay time in milliseconds  Will get processed only after the delay time mHandler.postDelayednew Runnable @Override public void run // update UI in main after 1 sec , 1000;
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 Activity.runOnUiThread  An alternative to Handler  Passed a Runnable  If the current thread is a background thread, behaves like post  If the current thread is the UI thread, executes Runnable immediately  Good for utility code that might be used in different places
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 AsyncTask  Bundles thread creation and inter-thread communication in one class  Extends and override all runs in UI thread except doInBackground  onPreExecute : after the task is executed  doInBackgroundParams... : after onPreExecute  onProgressUpdateProgress... : after publishProgressProgress... in doInBackground  onPostExecuteResult : after completion of doInBackground  Create an instance and executeParams...
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 Extends AsyncTask to obtain an inner class  AsyncTask is defined by 3 generic types Params, Progress, Result e.g. String, Integer, Boolean, Void, Void, Void  Params: the type of the parameters sent to the task upon execution  Progress: the type of the progress units published during the background computation  Result: the type of the result of the background computation
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class RefreshTask extends AsyncTaskVoid, Void, Void
@Override protected Void onPreExecute // prepare the UI before the task is run progressBar.setVisibilityView. VISIBLE ;
@Override protected Void doInBackgroundVoid... params // long running process
@Override protected Void onPostExecuteVoid result // update the UI after task is done progressBar.setVisibilityView. INVISIBLE ;

 Using AsyncTask
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class RefreshTask extends AsyncTaskString, Void, Boolean
@Override protected Boolean doInBackgroundString... params String url = params0; // get the 1st parameter // long running process return true;
@Override protected Void onPostExecuteBoolean result ifresult // handle successful task

 Using AsyncTask with parameters
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class RefreshTask extends AsyncTaskVoid, Integer, Void
@Override protected Void doInBackgroundVoid... params // long running process publishProgresscount; // long running process
@Override protected Void onProgressUpdateInteger... values int progress = values0; // update the progress bar

 Using AsyncTask – publish progress
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 Running AsyncTask new RefreshTask.execute;  Running AsyncTask with parameters new RefreshTask.execute“http://www.android.com”; new RefreshTask.execute1, 2, 3;  Running multiple AsyncTask in parallel  Default behaviour for API Level lower than 11  For API Level 11 or higher new RefreshTask.executeOnExecutorAsyncTask. THREAD_POOL_EXECUTOR;