Update UI from Thread in Android

Question

I want to update my UI from a Thread which updates a Progressbar  Unfortunately  when updating the progressbar s drawable from the  runnable  the progressbar disappears   Changing the progressbars s drawable in onCreate   on the otherside works   Any Suggestions   public void onCreate Bundle savedInstanceState        res   getResources        super onCreate savedInstanceState       setContentView R layout gameone       pB setProgressDrawable getResources   getDrawable R drawable green        Works        handler postDelayed runnable  1             private Runnable runnable   new Runnable         public void run               runOnUiThread new Runnable                  public void run                                       The Complete ProgressBar does not appear                                             pB setProgressDrawable getResources   getDrawable R drawable green

User · Answer

You need to create a Handler in the UI thread and then use it to post or send a message from your other thread to update the UI

User · Answer

Use the AsyncTask class  instead of Runnable   It has a method called onProgressUpdate which can affect the UI  it s invoked in the UI thread

User · Answer

You should do this with the help of AsyncTask  an intelligent backround thread  and ProgressDialog  AsyncTask enables proper and easy use of the UI thread  This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and or handlers   An asynchronous task is defined by a computation that runs on a background thread and whose result is published on the UI thread  An asynchronous task is defined by 3 generic types  called Params  Progress and Result  and 4 steps  called begin  doInBackground  processProgress and end   The 4 steps  When an asynchronous task is executed  the task goes through 4 steps   onPreExecute    invoked on the UI thread immediately after the task is executed  This step is normally used to setup the task  for instance by showing a progress bar in the user interface   doInBackground Params      invoked on the background thread immediately after onPreExecute   finishes executing  This step is used to perform background computation that can take a long time  The parameters of the asynchronous task are passed to this step  The result of the computation must be returned by this step and will be passed back to the last step  This step can also use publishProgress Progress     to publish one or more units of progress  These values are published on the UI thread  in the onProgressUpdate Progress     step   onProgressUpdate Progress      invoked on the UI thread after a call to publishProgress Progress      The timing of the execution is undefined  This method is used to display any form of progress in the user interface while the background computation is still executing  For instance  it can be used to animate a progress bar or show logs in a text field   onPostExecute Result   invoked on the UI thread after the background computation finishes  The result of the background computation is passed to this step as a parameter  Threading rules  There are a few threading rules that must be followed for this class to work properly   The task instance must be created on the UI thread  execute Params     must be invoked on the UI thread  Do not call onPreExecute    onPostExecute Result   doInBackground Params      onProgressUpdate Progress     manually  The task can be executed only once  an exception will be thrown if a second execution is attempted    Example code What the adapter does in this example is not important  more important to understand that you need to use AsyncTask to display a dialog for the progress   private class PrepareAdapter1 extends AsyncTask lt Void Void ContactsListCursorAdapter  gt        ProgressDialog dialog       Override     protected void onPreExecute             dialog   new ProgressDialog viewContacts this           dialog setMessage getString R string please wait while loading            dialog setIndeterminate true           dialog setCancelable false           dialog show                  non-Javadoc          see android os AsyncTask doInBackground Params                 Override     protected ContactsListCursorAdapter doInBackground Void    params            cur1   objItem getContacts            startManagingCursor cur1            adapter1   new ContactsListCursorAdapter  viewContacts this                  R layout contact for listitem  cur1  new String       new int                 return adapter1             protected void onPostExecute ContactsListCursorAdapter result            list setAdapter result           dialog dismiss

User · Answer

If you use Handler  I see you do and hopefully you created its instance on the UI thread   then don t use runOnUiThread   inside of your runnable  runOnUiThread   is used when you do smth from a non-UI thread  however Handler will already execute your runnable on UI thread   Try to do smth like this   private Handler mHandler   new Handler    public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       setContentView R layout gameone       res   getResources           pB setProgressDrawable getResources   getDrawable R drawable green        Works       mHandler postDelayed runnable  1      private Runnable runnable   new Runnable         public void run             pB setProgressDrawable getResources   getDrawable R drawable green            pB invalidate       maybe this will even not needed - try to comment out

User · Answer

The most simplest solution I have seen to supply a short  execution to the UI thread is via the post   method of a view  This is needed since UI methods are not re-entrant  The method for this is   package android view   public class View   public boolean post Runnable action     The post   method corresponds to the SwingUtilities invokeLater    Unfortunately I didn t find something simple that corresponds to  the SwingUtilities invokeAndWait    but one can build the later based on the former with a monitor and a flag   So what you save by this is creating a handler  You simply need to find your view and then post on it  You can find your view via  findViewById   if you tend to work with id-ed resources  The resulting code is very simple      inside your non-UI thread     view post new Runnable             public void run                    the desired UI update                          Note  Compared to SwingUtilities invokeLater   the method  View post   does return a boolean  indicating whether the  view has an associated event queue  Since I used the  invokeLater   resp  post   anyway only for fire and forget   I did not check the result value  Basically you should  call post   only after onAttachedToWindow   has been called  on the view    Best Regards

User · Answer

As recommended by official documentation  you can use  AsyncTask to handle work items shorter than 5ms in duration  If your task take more time  lookout for other alternatives    HandlerThread  is one alternative to Thread or AsyncTask  If you need to update UI from HandlerThread  post a message on UI Thread Looper and UI Thread Handler can handle UI updates    Example code   Android  Toast in a thread

User · Answer

If you don t like the AsyncTask you could use the observer pattern   In that example use the ResponseHandler as an inner class in your activity then have a string message that will set the progress bars percentage     You would need to make sure that any alterations to the UI are performed within the ResponseHandler to avoid freezing up the UI  then your worker thread  EventSource in the example  can perform the tasks required   I would use the AsyncTask tho  however the observer pattern can be good for customization reasons  plus its easier to understand   Also im not sure if this way is widely accepted or will 100  work   Im downloading and the android plugin now to test it

[android] Update UI from Thread in Android

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