ALAA M. ALSALEHI SOFTWARE ENGINEER AT IUG Multithreading in Android

Agenda Multithreading vocabulary Main thread in android Time-consuming & blocking operations Unresponsive program Thread safety in android Message Passing is the solution Timer & Timer Task AsyncTask

Multithreading vocabulary Thread vs. process Multithreading Synchronization Thread safe Lock Design Pattern Message Passing Pattern Volatile Swing multithreading Swing utility Swing worker

Main thread All Android application components run on the main application thread  Activities, Services, and Broadcast Receivers Time-consuming Blocking operation In any component  will block all other components including Services and the visible Activity

Time-consuming & blocking operations File operations Network lookups Database transactions Complex calculations etc

Unresponsive program Android OS save himself from application does not response for input events. Unresponsive program Activities  within 5 seconds Broadcast Receivers  onReceive handlers within 10 seconds.

Unresponsive Exception

Solution Create your own thread private void doLongOperationInThread() {  (new Thread(new Runnable() {  public void run() { String result = doLongOperation();  }  })).start(); }

What about update UI from other thread? private void doLongOperationInThread() {  (new Thread(new Runnable() {  public void run() { String result = doLongOperation(); updateUI(result);  }  })).start(); }

Thread safety in android

Exception FATAL EXCEPTION: Thread-10 android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views. at android.view.ViewRoot.checkThread(ViewRoot.java:2932) at android.view.ViewRoot.invalidateChild(ViewRoot.java:642) at android.view.ViewRoot.invalidateChildInParent(ViewRoot.java:668) at android.view.ViewGroup.invalidateChild(ViewGroup.java:2511) at android.view.View.invalidate(View.java:5279) at android.widget.TextView.checkForRelayout(TextView.java:5507) at android.widget.TextView.setText(TextView.java:2724) at android.widget.TextView.setText(TextView.java:2592) at android.widget.TextView.setText(TextView.java:2567) at com.modonat.threadNeed.ThreadNeedActivity.updateUI(ThreadNeedActivity.java:46) at com.modonat.threadNeed.ThreadNeedActivity.access$2(ThreadNeedActivity.java:44) at com.modonat.threadNeed.ThreadNeedActivity$2.run(ThreadNeedActivity.java:34) at java.lang.Thread.run(Thread.java:1019)

Is android UI thread-safe? Unfortunately like swing the answer will be No. Fortunately android has a good solution for this problem. Main thread who has control on UI Other thread who is doing long/blocking operatiions Create Update UI

Message Passing Android depend on message passing to solve this problem.

Handler private void updateUIByHandler() { final Handler myHandler = new Handler() public void handleMessage(Message msg) { updateUI((String) msg.obj); } }; (new Thread(new Runnable() { public void run() { Message msg = myHandler.obtainMessage();//get message object msg.obj = doLongOperation(1000); myHandler.sendMessage(msg);//send message to handle it } })).start(); }

Timer Like thread like timer in UI update. Timer timer=new Timer(); timer.schedule(new TimerTask() {  public void run() {  Message msg = myHandler.obtainMessage();  msg.obj = doLongOperation(1000);  myHandler.sendMessage(msg);} }, 1000);

AsyncTask onPreExecute  is invoked before the execution. onPostExecute  is invoked after the execution. doInBackground  the main operation. Write your heavy operation here. onProgressUpdate  Indication to the user on progress. It is invoked every time publishProgress() is called.

Refrence Android in Practice by CHARLIE COLLINS, MICHAEL D. GALPIN and MATTHIAS KÄPPLER Professional Android™ Application Development by Reto Meier Article “Android – Multithreading in a UI environment” id-multithreading-in-a-ui-environment/ id-multithreading-in-a-ui-environment/