PREP AsyncTask
Layout
<?xml version="1.0" encoding="utf-8"?>
LinearLayoutxmlns:android="
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="vertical"
android:padding="16dp"
<Button
android:id="@+id/btnSlow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="6dp"
android:ems="15"
android:text="Slow work -- AsyncTask"/>
<Button
android:id="@+id/btnQuick"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="6dp"
android:ems="15"
android:text="Push me anytime!"/>
<TextView
android:id="@+id/txtMsg"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="6dp"
android:background="#fcfc78"/>
</LinearLayout
Main Activity
package matos.csu.a09_04_asynctask;
public class MainActivityextends AppCompatActivity {
Button btnSlowWork;
Button btnQuickWork;
TextViewtxtMsg;
Long startingMillis;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txtMsg= (TextView) findViewById(R.id.txtMsg);
// lazy way out of multitasking - UI will run slow operations (NOT recommended)
// ------
// StrictMode.ThreadPolicy policy = new
// StrictMode.ThreadPolicy.Builder().permitAll().build();
// StrictMode.setThreadPolicy(policy);
// ------
// slow work...for example: delete all records stored in a large database
btnSlowWork= (Button) findViewById(R.id.btnSlow);
this.btnSlowWork.setOnClickListener(new View.OnClickListener() {
public void onClick(final View v) {
//anonymous asynctask -- passing two String input arguments
new VerySlowAsyncTask().execute("dummy1", "dummy2");
}
});
btnQuickWork= (Button) findViewById(R.id.btnQuick);
// quick response – display date-time on the UI
this.btnQuickWork.setOnClickListener(new View.OnClickListener() {
public void onClick(final View v) {
txtMsg.setText((new Date()).toString());
}
});
}// onCreate
// define the inner AsyncTask class
private class VerySlowAsyncTaskextends AsyncTask<String, Long, Void> {
String waitMsg= "Please wait - Slow job is being done...";
private final ProgressDialogdialog = new ProgressDialog(MainActivity.this);
protected void onPreExecute() {
//prepare dialog box to keep user informed - we have full access to the UI thread here
startingMillis= System.currentTimeMillis();
txtMsg.setText("Starting date:\n" + Calendar.getInstance().getTime());
this.dialog.setMessage(waitMsg);
this.dialog.setCancelable(false); //don't DISMISS box with outside touches
//this.dialog.getWindow().setGravity(Gravity.BOTTOM); //show at the bottom of screen
this.dialog.show();
}
// doing the busy work - UI cannot be directly modified here
protected Void doInBackground(final String... args) {
// show on Log.e the incoming dummy arguments - for instance database name, location
Log.e("doInBackground>", "Total args: " + args.length);
Log.e("doInBackground>", "args[0] = " + args[0] ); //dummy1
Log.e("doInBackground>", "args[1] = " + args[1] ); //dummy2
final long MAX_CYCLES = 5; //
try {
// simulate here the slow activity
for (Long counter = 1L; counter <= MAX_CYCLES; counter++) {
Thread.sleep(5000); //sleep for 5 seconds
publishProgress((Long) counter, (long) MAX_CYCLES); //send progress reports
}
} catch (InterruptedException e) {
Log.e("slow-job interrupted", e.getMessage());
}
return null;
}
// periodic UI updates - tell the user what is happening - you may update the UI
@Override
protected void onProgressUpdate(Long... progValue) {
super.onProgressUpdate(progValue);
//receiving two arguments in args array: currentCycle and MAX_CYCLES
long currentCycle = progValue[0];
long totalCycles = progValue[1];
dialog.setMessage( waitMsg
+ "\nHas completed " + currentCycle + " of " + totalCycles);
txtMsg.append("\nFinished step..." + currentCycle );
}
// we have full access to the UI here
protected void onPostExecute(final Void unused) {
if (this.dialog.isShowing()) {
this.dialog.dismiss();
}
// cleaning-up, all done
long totalSeconds = (System.currentTimeMillis() - startingMillis) / 1000;
txtMsg.append("\n\nElapse time: "+ totalSeconds + " sec."); //ok to change UI
txtMsg.append("\nAll done!");
}
}// AsyncTask
}// MainActivity
Comments
AsyncTask Template
public class MyBusyAsyncTaskTemplateextends AsyncTaskString, Long, Void> {
public MyBusyAsyncTaskTemplate (){
//optional - you may get a reference to MainActivity to manage its UI from here
}
protected void onPreExecute() {
// optional - prepare reporting tool (usually a ProgressDialog box) - may update UI
}
protected Void doInBackground(final String... args) {
// this is the SLOW background thread taking care of heavy tasks - cannot change UI
...
publishProgress((Long) someLongValue);
...
}
@Override
protected void onProgressUpdate(Long... value) {
// periodic updates - it is OK to change UI
}
protected void onPostExecute(final Void unused) {
// All done! - return results (if any) - may update UI from here
}
}
public Integer sum(Integer... items) {
intaccum = 0;
for (inti = 0; iitems.length; i++) {
accum += items[i];
}
return accum;
}
NOTE: If wanted, you may customize the dialog box – Create a new Activity showing custom layout, program its listeners.
MyCustomDialog dialog = new MyCustomDialog(); dialog.show();