1. Android
Threading
Jussi
Pohjolainen
Tampere
University
of
Applied
Sciencs

2. UI
Thread
• When
Android
app
is
launched
one
thread
is
created.
This
thread
is
called
Main
Thread
or
UI
Thread
• UI
Thread
is
responsible
for
dispatching
events
to
widgets
• Avoid
doing
0me
consuming
tasks
in
UI
Thread
since
it
leads
to
app
that
does
not
respond
quickly

3. TesAng
UI
Responsivess
public class ThreadExample extends Activity implements OnClickListener {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Button button = new Button(this);
button.setText("Do Time Consuming task!");
setContentView(button);
button.setOnClickListener(this);
}
@Override
public void onClick(View v) {
try {
for(int i=0; i<10; i++) {
System.out.println(i);
Thread.sleep(10000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

4. Result

5. TesAng
Separate
Thread
public class ThreadExample extends Activity implements OnClickListener, Runnable {
...
@Override
public void onClick(View v) {
Thread thread = new Thread(this);
thread.start();
}
@Override
public void run() {
try {
for(int i=0; i<10; i++) {
System.out.println(i);
Thread.sleep(10000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

7. How
about
influencing
the
UI?
...
@Override
public void run() {
try {
for(int i=0; i<10; i++) {
button.setText("Iteration: " + i);
Thread.sleep(1000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
...

8. Problem

9. Why?
• Android
UI
Toolkit
is
not
thread
safe
• If
you
want
to
manipulate
UI,
you
must
do
it
inside
the
UI
thread
• How
do
you
do
it
then?
You
can
use
– Activity.runOnUiThread(Runnable)
– View.post(Runnable)
– View.postDelayed(Runnable, long)
– …

10. Activity.runOnUiThread(Runnable)
• The
given
acAon
(Runnable)
is
executed
immediately
if
current
thread
is
UI
thread
• If
current
thread
is
NOT
UI
thread,
the
acAon
(Runnable)
is
posted
to
event
queue
of
the
UI
Thread

11. Example
of
RunOnUiThread
public class ThreadExample extends Activity implements OnClickListener, Runnable {
...
@Override
public void onClick(View v) {
Thread t = new Thread(this);
t.start();
}
public void run() {
// lengthy operation
try {
Thread.sleep(2000);
} catch (InterruptedException e) { }
runOnUiThread(new Update());
}
class Update implements Runnable {
// This action is posted to event queue
public void run() {
button.setText("Finished!");
}
}
}

12. View.post(Runnable)
View.postDelayed(Runnable, Long)
• These
methods
are
of
view
and
are
use
for
updaAng
the
view
• AcAon
(Runnable)
is
placed
on
Message
Queue
• Runnable
acAon
runs
on
UI
Thread
• postDelayed
method
for
delayed
acAon

13. Using
post
private int iteration;
...
@Override
public void run() {
try {
for(int i=0; i<10; i++) {
iteration = i;
button.post(new InfluenceUIThread());
Thread.sleep(1000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
class InfluenceUIThread implements Runnable {
public void run() {
button.setText("Iteration = " + iteration);
}
}

14. Using
Anonymous
Inner
Classes
@Override
public void onClick(View v) {
new Thread(new Runnable() {
public void run() {
try {
for(int i=0; i<10; i++) {
iteration = i;
button.post(new Runnable() {
public void run() {
button.setText("Iteration = " + iteration);
}
});
Thread.sleep(1000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
}
This
can
be
really
confusing...

15. AsyncTask
• Goal:
take
care
thread
management
for
you
• Use
it
by
subclassing
it:
class
MyTask
extends
AsyncTask
• Override
onPreExecute(),
onPostExecute()
and
onProgressUpdate()
– Invokes
in
UI
Thread
• Override
doInBackground()
– Invokes
in
worker
thread

16. Example
(Google
SDK)
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
}
return totalSize;
}
protected void onProgressUpdate(Integer... progress) {
setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) {
showDialog("Downloaded " + result + " bytes");
}
}
new DownloadFilesTask().execute(url1, url2, url3);
Params,
Progress,
Result

17. public class ThreadExample extends Activity implements OnClickListener {
private Button button;
...
class MyBackgroundTask extends AsyncTask<Integer, Integer, Integer> {
protected Integer doInBackground(Integer... ints) {
int i = ints[0];
try {
for(i=0; i<10; i++) {
System.out.println("doInBackground!");
publishProgress(new Integer(i));
Thread.sleep(1000);
}
} catch(Exception e) {
e.printStackTrace();
}
return i;
}
protected void onProgressUpdate(Integer iteration) {
button.setText("Iteration = " + iteration);
}
protected void onPostExecute(Integer result) {
button.setText("Finished with result of: " + result);
}
}
}