Develop Reference

Best practice to create a thread that runs every hour in Android?

So I'm attempting to create background task that needs to be run every hour in an Android app. Its a rather heavy task that takes around 5 - 10 minutes to finish, and right now it runs on the UI thread which of course isn't good, because it hangs the whole application. I've attempted the following in my MainActivity onCreate:
new Thread(new Runnable() {
private Handler HeavyTaskHandler = new Handler(Looper.getMainLooper());
public void run(){
final TextView updatedTxt = findViewById(R.id.txt);
updatedTxt.post(new Runnable() {
#Override
public void run() {
updatedTxt.setText("Performing cleanup..");
}
});
HeavyTask(); // <-- This method runs for 5 - 10 minutes
updatedTxt.post(new Runnable() {
#Override
public void run() {
updatedTxt.setText("Done..");
}
});
HeavyTaskHandler.postDelayed(this, HeavyTaskCycle);
}
}).start();
I have two issues with the above
It works fine the first time, and the task is performed in the background well without hanging the UI thread. However, after this first time and the next time(s) it is run, the UI thread hangs again when it is run. What am I missing?
Notice that before the HeavyTask() method is called i try to set a TextViews text to "Performing cleanup.." .. This never shows, only the "Done.." which happens after the HeavyTask() method is done. How can i ensure that the message also appears before?

I ended up doing the following from MainActivity which doesn't hang the application
private void CreateCleanUpThread()
{
CleanUpThread = new Thread(new Runnable() {
public void run(){
try {
while(true) {
performingCleanup = true;
final TextView updatedTxt = findViewById(R.id.updated_txt);
runOnUiThread(new Runnable() {
#Override
public void run() {
updatedTxt.setText("Performing database history cleanup..");
}
});
HeavyTask(); // <-- This method runs for 5 - 10 minutes
runOnUiThread(new Runnable() {
#Override
public void run() {
updatedTxt.setText("Done..");
}
});
performingCleanup = false;
Thread.sleep(CleanUpCycle); // 1 hour wait time
}
} catch(Exception ex) {
System.out.println("Error in CreateCleanUpThread : " + ex.getMessage());
}
}
});
}
// onCreate in MainActivity
...
CleanUpThread.start();
Certainly not the best way, but it works and will do for now. Should be moved to a service instead i think.

runOnUiThread() no executing when using Thread.sleep()

I'm using code that looks like this :
_thread = new Thread(){
#Override
public void run() {
try {
while (true) {
operate();
Thread.sleep(DELAY);
}
} catch (InterruptedException e) {
// Doesn't matters...
}
}
};
operate function looks like this :
// does things....
activity.runOnUiThread(new Runnable() {
#Override
public void run() {
// adds an ImageView to the screen
}
});
// does other things...
At the bottom line, what i wanted to achieve is an operation that happens once in a while, without interrupting the main thread and the UI, something like a game-loop.
In the first 2 times that operate() runs, it adds the ImageView and everything is alright, but after 2 or 3 times it stops adding the ImageViews, but the UI is still running as usual. When i debugged the problem, i found out that after 3 times the run() method of the Runnable isn't called anymore, even thought the operate function was called.
The wired thing (for me) was that when i removed the Thread.sleep, everything worked fine (much faster of course...). I tried to replace it with a very long for loop (just for checking) and it worked, but of course it is not an appropriate solution to the problem.
I read about the problem, most of the people that asked this question did a thread.sleep or an infinite loop on the main thread, but, as i see it, i didn't do such thing. Many people wrote that you should replace the Thread.sleep with Handler.postDelayed. I tried to do it but it didn't work, maybe I did it wrong. I even tried replacing the runOnUiThread with other options I found on the internet, but all of them gave me the same exact results. I tried to replace the method that I'm adding the view to the activity, but all of them, again, gave the same result.
The waiting is crucial for this application. I got to find a way to wait sometime and then execute a function on the UI thread, cause this pattern returns at least a couple of times in my application.

It sounds like you want a post delay so that you can do the code on the UI thread after some delay. Handler Post Delay.
private static final int DELAY = 500;
private Handler mHandler;
private Runnable mRunnable;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
start();
}
private void start()
{
mHandler = new Handler();
mRunnable = new MyRunnable(this);
mHandler.postDelayed(mRunnable, DELAY);
}
private void stop()
{
mHandler.removeCallbacks(mRunnable);
}
private void doSomething()
{
// Do your stuff here.
// Reschedule.
mHandler.postDelayed(mRunnable, DELAY);
}
Recommended way of creating a Runnable.
private static class MyRunnable implements Runnable
{
private WeakReference<MainActivity> mRef;
// In here you can pass any object that you need.
MyRunnable(MainActivity activity)
{
mRef = new WeakReference<MainActivity>(activity);
}
#Override
public void run()
{
// Safety check to avoid leaking.
MainActivity activity = mRef.get();
if(activity == null)
{
return;
}
// Do something here.
activity.doSomething();
}
}

There could be several reasons why the UI Runnable isn't being executed. Probably the activity variable has something messed up with it or it's referencing the context incorrectly, or as you said the Thread.sleep() could be causing an issue. At this point more parts of the code needs to viewed to better solve the problem.
A better way of implementing your logic is to use a scheduled Timer instead of using an infinite loop with a Thread.sleep() in it. It will execute the code within a background thread. And then use a Handler to update the UI instead of activity.runOnUiThread(). Here's an example:
// Global variable within the activity
private Handler handler;
// Activity's onCreate()
#Override
protected void onCreate(Bundle savedInstanceState) {
handler = new Handler(getMainLooper());
Timer timer = new Timer("ScheduledTask");
// Timer must be started on the Main UI thread as such.
timer.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
operate();
}
}, 0L, DELAY);
}
private void operate() {
// does things in background....
handler.post(new Runnable() {
#Override
public void run() {
// adds an ImageView to the screen from within the Main UI thread
}
});
// does other things in the background...
}

Thread is able to change ui if started from inside activity lifecycle methods. why?

I was testing this code to check if app crashes for changing ui component from background thread. but it didn't.
Here in the code added below. I started a new thread in onCreate() method of MainActivity and It should have crashed as per the android docs which says
In the class, the Runnable.run() method contains the code that's
executed. Usually, anything is allowable in a Runnable. Remember,
though, that the Runnable won't be running on the UI thread, so it
can't directly modify UI objects such as View objects.
So I was expecting it to crash. Which it didn't. See code -
public class MainActivity extends AppCompatActivity {
TextView txt;
Thread thread;
Runnable runnable = new Runnable() {
#Override
public void run() {
txt.setText("bro");
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txt = (TextView) findViewById(R.id.name_txt);
thread = new Thread(runnable);
thread.start();
}
}
While if i try changing ui while starting thread from onClicklistener() as below it does crash. which is expected.
public class MainActivity extends AppCompatActivity {
TextView txt;
Thread thread;
Runnable runnable = new Runnable() {
#Override
public void run() {
txt.setText("bro");
}
};
View.OnClickListener listener = new View.OnClickListener() {
#Override
public void onClick(View v) {
thread.start();
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txt = (TextView) findViewById(R.id.name_txt);
thread = new Thread(runnable);
txt.setOnClickListener(listener);
}
}
Now, that the second code snippet crashes, which is expected and the first one doesn't.
Please explain why is this happening, as I'm creating a new worker thread each time but just at different places. Official docs reference will be appreciated.

I found the reason behind this behavior as pointed out by #krish in the comments on my question. The reason is that, the thread was able to make changes in the TextView object only till it was not visible on UI screen i.e not rendered. It is only after the view rendering, that any thread except the Main thread may not make changes to any UI components. I Tried using view observer to see if the view was rendered before the changes or not. which showed that changes were made before the view rendering.
Here is the code that i tried.
public class MainActivity extends AppCompatActivity {
TextView txt;
Thread thread;
Runnable runnable = new Runnable() {
#Override
public void run() {
txt.setText("bro");
Log.d("ThreadTest", "The Text was changed.");
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txt = (TextView) findViewById(R.id.name_txt);
thread = new Thread(runnable);
txt.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
Log.d("ThreadTest", "The TextView was rendered");
}
});
}
#Override
protected void onResume() {
super.onResume();
thread.start();
}
}
Using the code above. You'll see in the output:
The Text was changed.
The TextView was rendered
Which means text was changed before view rendering. if you try to start thread to makes changes in onGlobalLayout method. App crashes as it should.

The UI is not thread-safe see processes-and-threads, so you were just lucky you did not hit one of the many landmines waiting for you.
If you don't like relying on luck then:
You should be using:
runOnUiThread(runnable);
instead of:
thread = new Thread(runnable);
AsyncTask enables proper and easy use of the UI thread.

Threads cannot start in android

I have a problem with my Thread, the Thread doesn't start, I don't have any idea why it doesn't run.
This is my code,
public class MainActivity extends AppCompatActivity {
TextView tv;
int seg=0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv=(TextView)findViewById(R.id.reloj);
}
boolean on=false;
public void inicia(View view){
if(!on){
tiempo.start();
on=true;
}
}
Thread tiempo=new Thread(){
public void run(){
try{
while(true){
Thread.sleep(1000);
seg++;
tv.setText(seg+"");
}
}catch (InterruptedException e){
}
}
};
}
prints this error
Only the original thread that created a view hierarchy can touch its views.

Well first off I'm assuming you set an onClick in you xml to set inicia to be the click handler for the button. Otherwise, that's part of your problem.
You thread is in an infinite loop. The while loop would only exit if an interrupt occurred for some reason, and there's nothing that would do that. If you want to post accio every second, the post needs to be inside the while loop.

while(true){
Thread.sleep(1000);
}
The thread is sleeping all the time.

Ok lets try,
Thread will be created from the main looprer thread. So, Your textview will be updated only by mainlooper thread,. When you create the thread, it will start become another thread. it is not related with MainLooper thread, You have to use Handler class to update the textView or use Asynctask or runOnUiThread method to update your text view.
runOnUiThread(new Runnable() {
#Override
public void run() {
textview.settext("");
}
});

Display message on non-stop thread

Following code is within an android activity class.
The project required a non-stop thread when apps is active and stop when apps is inActive/closed.
I predicted to see a non-stop "Hello World" message display in logCat.However I only saw one-times Hello World messgae .
What wrong of my code,so that I able to see a non-stop "Hello World"
Hope someone advice. Thanks
#Override
protected void onStart(){
super.onStart();
Log.e("onStart","beforeStart");
new HttpRequestTask().execute();
Log.e("onStart","Start");
this.pickButtonThread();
}
private void pickButtonThread(){
new Thread() {
#Override
public void run() {
try {
// code runs in a thread
PickerItemActivity.this.runOnUiThread(new Runnable() {
#Override
public void run() {
// code runs in a UI(main) thread
//isPickButtonEnableDisable();
//new HttpRequestTask().execute();
Log.e("pickButtonThread", "Hello World");
}
});
} catch (final Exception ex) {
}
}
}.start();
}

That's because you don't have any loop inside your run() method, thus it's run just once and it exits. However, declaring an endless loop is not considered a good idea as Android OS might kill it if there's lack of memory.
You could use a Handler using the .postDelayed() method to post messages every X seconds.
private Handler mHandler = new Handler();
private Runnable mUpdateTimeTask = new Runnable() {
public void run() {
Log.e("pickButtonThread", "Hello World");
mHandler.postDelayed(this, 1000); // Every second
}
};