1. Cosc 5/4730 A little on threads and Messages: Handler class

2. Messages. Only the activity thread can change the “screen” widgets. – So if you start a thread up, then you have send messages back to main thread to change a widget. – So you need to pieces. A message handler (normally in Oncreate() ) to receive messages And a way to send those messages.

3. Simple messages In many cases you may only need to send a message, more like a “poke”. – “Do something, you know that one!” kind of message – Hander.sendEmptyMessage(int); Where the receiving side, gets a number.

4. Simple messages OnCreate() handler = new Handler() { @Override public void handleMessage(Message msg) { if (msg.what == 0) { //do whatever msg 0 is. } //check for other message as needed. } Thread handler.sendEmptyMessage(0) ;

5. Message with a little information. In the handle you can get a Message object – Message msg = handler.obtainMessage(); Message has a “what” like the simple message – and int arg0, arg1 – So you can send two pieces of integer information. – Then you send that message – Handler.sendMessage(msg);

6. information messages OnCreate() handler = new Handler() { @Override public void handleMessage(Message msg) { if (msg.what == 1) { int arg1 = msg.arg1; Int arg2 = msg.arg2; } //check for other message as needed. } Thread Message msg = handler.obtainMessage(); //setup the message msg.what = 1; msg.arg1 = 1; msg.arg2= 3012; handler.sendMessage(msg);

7. Sending lots of information. Besides the two arg variables, you can set a bundle in the message as well. – So if you want send more then two integer – Or you want to send any other type, say strings.

8. Sending lots of information OnCreate() handler = new Handler() { @Override public void handleMessage(Message msg) { if (msg.what == 3) { Blunde stuff = msg.getData(); str1 = stuff.getString(“key2”); … } //check for other message as needed. } Thread Message msg = handler.obtainMessage(); Bundle b = new Bundle(); b.putString(“key”, “Stuff”); b.putString(“key2”, “more Stuff”); //setup the message number msg.what = 3; Msg.setData(b); //add bundle handler.sendMessage(msg);

9. A note on threads Pausing threads. – If you want a running thread to “pause” and then start up again later. – Use the wait and notify methods in the Thread class. In the Running thread – It calls wait(); Then when the thread is to be woken up – Notify is called.

10. Example Main thread MyThread = new Thread (this); myThread.start(); … //wake up a thread pause = false; synchronized(myThread) { //wake up 1 thread myThread.notify(); // or myThread.notifyAll() to wake up all threads. } Thread If (pause) { //boolean try { synchronized(myThread) { myThread.wait(); } } catch (InterruptedException e) { ;// failed to wait! } }//end if //when notified, thread starts here. The ThreadDemo has working version of all this.

11. Q A &