Android Threading
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The document discusses Android threading and how to handle long running tasks to avoid blocking the UI thread. It covers the main UI thread, how to run tasks on a background thread using Thread and Runnable, and how to update the UI from the background thread using runOnUiThread(), post(), postDelayed() and AsyncTask. AsyncTask is recommended as it handles threading for you by running background tasks on a worker thread and calling publishProgress() to update the UI on the main thread.
![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](https://image.slidesharecdn.com/android-threading-140401044337-phpapp01/85/Android-Threading-16-320.jpg)
![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);
}
}
}](https://image.slidesharecdn.com/android-threading-140401044337-phpapp01/85/Android-Threading-17-320.jpg)
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Android Threading
- 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); } } }