Android Application and AsyncTask basics
Original Article: http://www.screaming-penguin.com/node/7746
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public class Main extends Activity { private static final String NAME = "NAME"; private EditText input; private Button saveButton; private Button deleteButton; private TextView output; private MyApplication application; @Override public void onCreate(final Bundle savedInstanceState) { Log.d(MyApplication.APP_NAME, "onCreate"); super.onCreate(savedInstanceSt<wbr>ate); this.setContentView(R.layout.m<wbr>ain); // get "Application" object for shared state or creating of expensive resources - like DataHelper // (this is not recreated as often as each Activity) this.application = (MyApplication) this.getApplication(); // inflate views this.input = (EditText) this.findViewById(R.id.in_text<wbr>); this.saveButton = (Button) this.findViewById(R.id.save_bu<wbr>tton); this.deleteButton = (Button) this.findViewById(R.id.del_but<wbr>ton); this.output = (TextView) this.findViewById(R.id.out_tex<wbr>t); // initially populate "output" view from database new SelectDataTask().execute(); // save new data to database (when save button is clicked) this.saveButton.setOnClickList<wbr>ener(new OnClickListener() { public void onClick(final View v) { new InsertDataTask().execute(Main.<wbr>this.input.getText().toString(<wbr>)); Main.this.input.setText(""); } }); // delete all data from database (when delete button is clicked) this.deleteButton.setOnClickLi<wbr>stener(new OnClickListener() { public void onClick(final View v) { new DeleteDataTask().execute(); } }); } @Override public void onSaveInstanceState(final Bundle b) { Log.d(MyApplication.APP_NAME, "onSaveInstanceState"); if ((this.input.getText().toStrin<wbr>g() != null) && (this.input.getText().toString<wbr>().length() > 0)) { b.putString(Main.NAME, this.input.getText().toString(<wbr>)); } super.onSaveInstanceState(b); } @Override public void onRestoreInstanceState(final Bundle b) { Log.d(MyApplication.APP_NAME, "onRestoreInstanceState"); super.onRestoreInstanceState(b<wbr>); String name = b.getString(Main.NAME); if (name != null) { // use onSaveInstanceState/onRestoreI<wbr>nstance state to manage state when orientation is changed (and whenever restarted) // many views already do this automatically, so this is a silly example, but you could save your own state here too this.input.setText(name); } } private class InsertDataTask extends AsyncTask<String, Void, Void> { private final ProgressDialog dialog = new ProgressDialog(Main.this); // can use UI thread here protected void onPreExecute() { this.dialog.setMessage("Insert<wbr>ing data..."); this.dialog.show(); } // automatically done on worker thread (separate from UI thread) protected Void doInBackground(final String... args) { Main.this.application.getDataH<wbr>elper().insert(args[0]); return null; } // can use UI thread here protected void onPostExecute(final Void unused) { if (this.dialog.isShowing()) { this.dialog.dismiss(); } // reset the output view by retrieving the new data // (note, this is a naive example, in the real world it might make sense // to have a cache of the data and just append to what is already there, or such // in order to cut down on expensive database operations) new SelectDataTask().execute(); } } private class SelectDataTask extends AsyncTask<String, Void, String> { private final ProgressDialog dialog = new ProgressDialog(Main.this); // can use UI thread here protected void onPreExecute() { this.dialog.setMessage("Select<wbr>ing data..."); this.dialog.show(); } // automatically done on worker thread (separate from UI thread) protected String doInBackground(final String... args) { List<String> names = Main.this.application.getDataH<wbr>elper().selectAll(); StringBuilder sb = new StringBuilder(); sb.append("Names in database:\n"); for (String name : names) { sb.append(name + "\n"); } return sb.toString(); } // can use UI thread here protected void onPostExecute(final String result) { if (this.dialog.isShowing()) { this.dialog.dismiss(); } Main.this.output.setText(resul<wbr>t); } } private class DeleteDataTask extends AsyncTask<String, Void, Void> { private final ProgressDialog dialog = new ProgressDialog(Main.this); // can use UI thread here protected void onPreExecute() { this.dialog.setMessage("Deleti<wbr>ng data..."); this.dialog.show(); } // automatically done on worker thread (separate from UI thread) protected Void doInBackground(final String... args) { Main.this.application.getDataH<wbr>elper().deleteAll(); return null; } // can use UI thread here protected void onPostExecute(final Void unused) { if (this.dialog.isShowing()) { this.dialog.dismiss(); } // reset the output view by retrieving the new data // (note, this is a naive example, in the real world it might make sense // to have a cache of the data and just append to what is already there, or such // in order to cut down on expensive database operations) new SelectDataTask().execute(); } } } |
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