Databases
StackOverflow2013
Postsdbo
POUpdating Views through AsyncTasks
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POUpdating Views through AsyncTasks
    primarykey
    data
    text
    <p>Below is working sample code of an Android Activity that has 2 buttons, of which only 1 is ever visible: a refresh button and a stop button.</p> <p>This code does the following:</p> <p>Refresh is clicked: start some AsyncTasks. The preExecute of the tasks will hide the refresh button and show the stop button. The postExecute of the task will check if there are no more running tasks and if so, show the refresh button and hide the stop button.</p> <p>Stop is clicked: all tasks are cancelled, the refresh button is shown and the stop button is hidden.</p> <p>This code works fine, but for one exception: when I recreate the activity while a task is running by changing the screen orientation. The buttons will now return to the state as defined in the xml (refresh=visibile, stop=gone).</p> <p>Using a static variable to keep track of the current state of the visibility only makes it worse, because the running Task that has to toggle it back, can only modify views in the calling activity, which has been stopped or destroyed at that point!</p> <pre><code>public class MainActivity extends Activity { private static List&lt;MyAsyncTask&gt; activeTasks = new LinkedList&lt;MyAsyncTask&gt;(); private View refresh; private View stop; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); this.setContentView(R.layout.activity_main); this.refresh = findViewById(R.id.refresh); this.refresh.setOnClickListener(new OnClickListener() { public void onClick(View v) { // Start a couple tasks new MyAsyncTask(MainActivity.this).execute(); new MyAsyncTask(MainActivity.this).execute(); } }); this.stop = findViewById(R.id.stop); this.stop.setOnClickListener(new OnClickListener() { public void onClick(View v) { // Cancel all tasks and toggle refresh button cancelAll(); MainActivity.this.enableRefresh(true); } }); } public void enableRefresh(boolean enable) { if (this.refresh != null &amp;&amp; this.stop != null) { this.refresh.setVisibility(enable ? View.VISIBLE : View.GONE); this.stop.setVisibility(!enable ? View.VISIBLE : View.GONE); } } public static void cancelAll() { for (MyAsyncTask task : MainActivity.activeTasks) task.cancel(true); MainActivity.activeTasks = new LinkedList&lt;MyAsyncTask&gt;(); } private class MyAsyncTask extends AsyncTask&lt;Void,Void,Void&gt; { private MainActivity activity; public MyAsyncTask(MainActivity activity) { this.activity = activity; } @Override protected void onPreExecute() { MainActivity.activeTasks.add(this); this.activity.enableRefresh(false); } @Override protected Void doInBackground(Void... v) { try { // Simulate a task Thread.sleep(3000); } catch (InterruptedException e) { } return null; } @Override protected void onPostExecute(Void v) { MainActivity.activeTasks.remove(this); if (MainActivity.activeTasks.size() == 0) this.activity.enableRefresh(true); } } } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USwvdz
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload