Develop Reference

Update Activity UI from a Timer , after restarting Activity

In the onCreate() method of my activity I have a Timer + TimerTask that will schedule a ParseQuery. On The ParseQuery callback, which is on mainThread, I delegate an interface callback to make a simple UI update. This works when I let the Activity unchanged. But if I exit from the activity and enter again it (A new timer will NOT be created here, because it gets created only when starting the activity from a certain point) wouldn't work. I think is something with Activity instances but I cannot handle it.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_chat);
....
uiTimer = new Timer();
uiTask = new TimerTask() {
#Override
public void run() {
doParseTask();
}
};
uiTimer.schedule(uiTask, shortCodeLeft);
}
doParseTask(){
Utils.doParseQuery(this, new MyListener{
#Override
public void onSuccess() {
updateUI();
}
});
}
updateUI(){
Log.i(TAG, "Show changed layout"); //This is always shown, this way I ensure it gets here!!
mTextView.setText(foo); //this doesn't work
mLayout.setVisibility(View.GONE); //this doesn't work
}
The ParseQuery is executed in done() callback method, I call the function that updates the UI:
public class Utils{
.......
doParseQuery(Context ctx, MyListener listener){
.......
query.saveInBackground(new SaveCallback() {
#Override
public void done(ParseException e) {
if(e == null){
....
listener.onSuccess();
}
}
});
}
}
What I have tried, with no success:
1. make the `uiTimer` and `uiTask` static global variables; // I thought that maybe it gets leaked into activity instances
2. update the UI using
runOnUiThread(new Runnable() {
#Override
public void run() {}
});
OR
mLayout.post(new Runnable() {
#Override
public void run() {
mLayout.setVisibility(View.GONE);
}
});
3. android:launchMode= "singleInstance" //in Manifest

If you want that your UITimer to gets executed every time your activity goes to foreground, you should implement the onStart or onResume method and move your uiTimer implementation to one of both method. Even your activity being already started these two methods are called after exiting the activity and reopening it again.
A better explanation of Android Activity lifecycle is well explained by google documentation https://developer.android.com/guide/components/activities/activity-lifecycle.html.
Your code would look like this:
#Override
protected void onStart() {
super.onStart();
....
uiTimer = new Timer();
uiTask = new TimerTask() {
#Override
public void run() {
doParseTask();
}
};
uiTimer.schedule(uiTask, shortCodeLeft);
}
doParseTask(){
Utils.doParseQuery(this, new MyListener{
#Override
public void onSuccess() {
updateUI();
}
});
}

When you exit from your activity, the instances mTextView and mLayout will be destroyed.
Then, when you create a new activity, the activity creates new instances of the text view and layout.
Your timer goes off and tries to update the original elements, which are now invalid as the activity has been closed (but the log still works as this is separate to your activity).
You should initialise the timer & task in onCreate(), and then in order to stop updating the old UI elements:
#Override
protected void onStop() {
if (uiTimer != null) {
uiTimer.cancel();
}
super.onStop();
}

android thread only runs once

I just wanted to test Log.i() and look at the console in android studio. In the code below onResume should start the thread and run() should write an endless stream of "dings" with the tag "run" in the monitor. But the run method apparently only gets called once. Why?
public class MainActivity extends Activity implements Runnable {
Thread gameThread = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.i("onCreate","getting started");
}
public void run() {
Log.i("run","ding");
}
#Override
public void onResume() {
super.onResume();
gameThread = new Thread(this);
gameThread.start();
}
}

You're missing the notion of what threading really does. It allows you to run a unit of work asynchronously. So, all the same normal rules apply. The reason it only runs once, is because the thread exits after run() returns. So just like any other method, you should put something like
while(true)
{
Log.i("run","ding");
}
inside of run(). Ideally you would actually check some condition so that you can exit the thread as needed.
Finally, it is probably a bad idea to have your MainActivity implement Runnable. Typically it is good style to have a thread implemented by its own class, for example DingThread implements Runnable.

You're missing while loop that why its run only once. Use below code. This is the better approach to use thread concept.
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.i("onCreate","getting started");
}
#Override
public void onResume() {
super.onResume();
startThread();// create thread obj and start
}
private GameThread mGameThread = null;
private void startThread() {
stopThread();// if thread already running stop it then create new thread and start (for avoiding multi-threading).
mGameThread = new GameThread();
mGameThread.start();//start the thread.
}
//To stop the thread simply call this method.
private void stopThread() {
if(mGameThread != null) {
mGameThread.setStop();
mGameThread = null;
}
}
private class GameThread extends Thread {
private boolean mIsStop;// mIsStop is default false
#Override
public void run() {
while (!mIsStop) { // if mIsStop is false then only come inside loop.
Log.i("run","ding"); //log will print
}
}
public void setStop() {
mIsStop = true;// set mIStop variable to true.
}
}
}

Get variable value from binded service in activity permanently

I have an activity thats already binded to the service.
When I start the activity, it binds to the service and gets a value from a variable inside the service. So I can display the value in my activity.
Now I want to read the value of the variable in the service permanently. Not only once while onCreate of my activity is called.
How can I do this?
Whats the right way for this?

There are several ways to accomplish that. One relatively easy way is to use a Handler that triggers itself periodically
public class MyActivity extends Activity {
private static final int UPDATE_RATE_IN_MS = 500;
private static final int MSG_UPDATE = 0;
private Handler mHandler;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
doUpdate();
mHandler.sendEmptyMessageDelayed(MSG_UPDATE, UPDATE_RATE_IN_MS);
}
};
}
#Override
protected void onStart() {
super.onStart();
mHandler.sendEmptyMessageDelayed(MSG_UPDATE, UPDATE_RATE_IN_MS);
}
#Override
protected void onStop() {
super.onStop();
mHandler.removeMessages(MSG_UPDATE);
}
private void doUpdate() {
// do whatever you need here.
}
}
You would put the update of the value in doUpdate() in this example.

Activity gets killed when orientation is changed

I have two activities in my project- Splash and AActivity. Splash is the main activity and is working fine. But if i change the orientation while Splash activity is running, the UI of splash activity goes off but it opens the AActivity after 10 sec.
code for splash activity is -
public class Splash extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.splash);
Thread timer = new Thread(){
public void run() {
try{
sleep(10000);
}catch(InterruptedException e){
e.printStackTrace();
}finally{
Intent AActivityIntent = new Intent("com.example.ex.AACTIVITY");
startActivity(AActivityIntent);
}
}};
timer.start();
}
#Override
protected void onPause() {
super.onPause();
finish();
}
}
I want to retain the UI of splash activity for 10 seconds even if orientation is changed. After 10 sec splash activity should be finished. How to do it ???

I suggest you doing the following:
public class Splash extends Activity {
private Thread timer;
private volatile long timeLeft;
private long timeStarted;
private long timeStopped;
private static final long TIME_TO_SHOW = 100000
private static final String KEY_TIME_LEFT = "timeLeftToRun";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.splash);
if (savedInstanceState != null) {
timeLeft = savedInstanceState.getLong(KEY_TIME_LEFT, 0);
} else {
timeleft = TIME_TO_SHOW;
}
timer = new Thread() {
public void run() {
try {
sleep(timeLeft);
Intent AActivityIntent = new Intent("com.example.ex.LISTSCREEN");
startActivity(AActivityIntent);
} catch(InterruptedException e) {}
}
}};
timeStarted = SystemClock.elapsedRealtime();
timer.start();
}
#Override
protected void onPause() {
super.onPause();
timer.interrupt();
timeStopped = SystemClock.elapsedRealtime();
finish();
}
#Override
protected void onSaveInstanceState(Bundle outState) {
timeLeft -= timeStopped - timeStarted;
if (timeLeft > 0) outState.putLong(timeLeft);
}
}
The main idea here is that you kill the thread if the activity is killed, but you take a note for how long it has run and how much time it has left. When the activity is restored, you do the same actions, except you have to wait for a smaller amount of time.
The code above is, of course, untested, but it should illustrate the idea.

Insert into your manifest these below block.
It means orientation change situation controlled by your "activity".
http://developer.android.com/guide/topics/manifest/activity-element.html#config
android:configChanges="orientation"
And more.
Override "onConfigurationChanged" method.
Try this. You can do everything you want.

Instead of using a Thread for delayed launch of activity use Alarmmanager, even if you are quitting the app you could always cancel the pending Alarm

Periodically refresh/reload activity

I have one activity. OnCreate the activity gets the source (html) of a web page to a string and presents the result (after parsing it a bit) in a textview.
I would like the activity to reload/refresh periodically to always present the latest information.
What is the best solution for this?

First of all... separate the updating logic from your onCreate method. So, for instance, you can create an updateHTML().
Then, you can use a Timer in order to update the page periodically:
public class YourActivity extends Activity {
private Timer autoUpdate;
public void onCreate(Bundle b){
super.onCreate(b);
// whatever you have here
}
#Override
public void onResume() {
super.onResume();
autoUpdate = new Timer();
autoUpdate.schedule(new TimerTask() {
#Override
public void run() {
runOnUiThread(new Runnable() {
public void run() {
updateHTML();
}
});
}
}, 0, 40000); // updates each 40 secs
}
private void updateHTML(){
// your logic here
}
#Override
public void onPause() {
autoUpdate.cancel();
super.onPause();
}
}
Notice that I'm canceling the updating task on onPause, and that in this case the updateHTML method is executed each 40 secs (40000 milliseconds). Also, make sure you import these two classes: java.util.Timer and java.util.TimerTask.