Activity onStart() operation results in a blank screen

Question

I am trying to automatically start a simple timer when the activity shows up. Currently, the activity will not load visibly until my operation is done. Should I override another method?

@Override
protected void onStart() {
    super.onStart();
    for (int i = 0; i <= 100; i++) {
        ((TextView) findViewById(R.id.timer)).setText(String.valueOf(i));
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
            Log.e("timer", e.getMessage());
        }
    }
}

your question says onStart() method while code is for onResume() method ? — Vivek Mishra, Oct 22 '18 at 05:40
Have a look at this. https://thealaskalinuxuser.wordpress.com/2017/04/04/countdown-or-runnable-and-handler-whats-the-difference/ You don't have to call Thread.sleep() — Janwilx72, Oct 22 '18 at 05:41

score 2 · Accepted Answer · answered Oct 22 '18 at 05:52

2

You are blocking main thread, use Handler with Runnable instead

handler = new Handler();

final Runnable r = new Runnable() {
    public void run() {
        tv.append("Hello World");
        handler.postDelayed(this, 1000);
    }
};

handler.postDelayed(r, 1000);

answered Oct 22 '18 at 05:52

Maksym V.

2,877
17
27

Does this cause the Runnable to possibly modify the TextView off the UI thread, and if so, is that going to be okay? – Yonatan Oct 22 '18 at 05:56
well it is not the best option, I would use MutableLiveData and databinding. In that way you will postValue which is thread safe. – Maksym V. Oct 22 '18 at 05:59
I understand that the issue is the main thread been blocked. How ever i am still interested for general knowledge to find out if there is another method that is called when the graphics are already been loaded and visible. – Rb87 Oct 23 '18 at 00:54

score 1 · Answer 2 · answered Oct 22 '18 at 05:55

Pausing the current thread in order to create a timer is a really bad idea.CheckOut Timer class and have a look at scheduleAtFixedRate() method in that class and extract ((TextView) findViewById(R.id.timer)) out from for loop.

have a look at How to set a Timer in Java?

score 1 · Answer 3 · answered Oct 23 '18 at 00:47

1

While activity running in onStart(),you may see part of your layout ,not all of your layout. Maybe you can override method onWindowFocusChanged(),and then start a Thread. And why you use 'super.onResume()' in onStart()? I don't understand:)

answered Oct 23 '18 at 00:47

Seraph Gabriel

51
7

Yeah, it's a copy paste mistake – Rb87 Oct 23 '18 at 01:01
But would onWindowFocusChanged() be called on different events? for instance screen orientation change? – Rb87 Oct 23 '18 at 01:03
1

All of the Window focus changed ,it will be called,include screen orientation change.The screen orientation change will destory current activity and reCreate it.Sometimes you must save the Activity state. – Seraph Gabriel Oct 23 '18 at 01:24

Activity onStart() operation results in a blank screen

3 Answers3