What is the correct way to use Handler and Runnable?

Question

I am developing an Android application and I want to call a function every 40ms. To do so, I implemented a Handler and a Runnable. I chose this two objects thanks to the post How to run a method every X seconds. But I am not sure this is the right way to perform what I am doing :

In my application, I am playing a video, I want to "launch" the Handler when starting the video, "put it on hold" when pausing the video, starting it again when resuming the video and so on.

So far, I am using mHandler.removeCallbacks(mRunnable); to detain it. But to start it or resume it, I don't know if I should use mHandler.post(mRunnable); mHandler.postDelay(mRunnable, DELAY) or mRunnable.run();. I succeed making them all work but the behaviour is never as expected...

Here is the code I use to set up the Handler...

public void setUpdatePositionHandler() {
    mHandler = new Handler();
    mRunnable = new Runnable() {
        @Override
        public void run() {
            if (mVideoView.getCurrentPosition() > mVideoView.getDuration()) {
                if (mVideoView.getCurrentPosition() > 1000) {
                    mVideoView.seekTo(1); // go back to beginning
                    mVideoView.pause();
                    mPlayButton.setVisibility(View.VISIBLE);
                    mStampIndex = 0;
                    mLastPosition = 0;
                    Log.i(TAG, "removeCallbacks() from runnable");
                    mHandler.removeCallbacks(this);
                } else {
                    //mHandler.postDelayed(this, DELAY);
                }
            } else {
                if (!mStamps.isEmpty()) {
                    onPositionUpdate(mStamps);
                }
                mHandler.postDelayed(this, DELAY);
            }
        }
    };

Note that I don't feel really sure of what I implemented so far, and that any ressources that would help me understand better would be welcome :) (I already read the documentations of the 2 classes and read several documents or posts on the subjects, but I think I am missing something.)

Thank you for your help

Can you explain why the behaviour is not what you are expecting? — Ivan, Oct 24 '18 at 08:18
you likely won't be able to run your code with such precision in time. — Vladyslav Matviienko, Oct 24 '18 at 08:24
@Ivan In one case, the runnable is running from the beginning of the video but doesn't stop when I pause the video. And in another case, it doesn't run on video launch but behave as expected when I pause and resume and pause again the video... — Juliette Marquis, Oct 24 '18 at 08:24
Handler.postDelayed will post a runnable to be run x miliseconds after it is issued. Handler.post will post a runnable to be run after all outstanding tasks on the main thread, from the point of post being called, are completed. — Thomas Cook, Oct 24 '18 at 08:26
You could use RX (if you don't mind bringing it as a dependancy), it let's you create really fluent timed loop. — Thomas Cook, Oct 24 '18 at 08:27
@ThomasCook Thank you for the details about the two functions. Afte reading the documentation, I thought Handler.post would post a runnable to be run when post() was called. For using RX, I will check it out, but I must say, I would really like to understand how Handlers and Runnables work together ahahha — Juliette Marquis, Oct 24 '18 at 08:41
Yea that is fair, always always always read the documentation. Also, you can download the source and look at it in your IDE - the ultimate source of truth (no pun intended) — Thomas Cook, Oct 24 '18 at 08:56

score 0 · Accepted Answer · answered Oct 24 '18 at 08:23

Is it the correct way ? if it will not produce any problem and it meets your requirements then yes but your question should be is it the best practice? i prefer to write it like the following

public void setUpdatePositionHandler() {
    mHandler = new Handler();
    mRunnable = new Runnable() {
        @Override
        public void run() {
            if (mVideoView.getCurrentPosition() > mVideoView.getDuration()) {
                if (mVideoView.getCurrentPosition() > 1000) {
                    mVideoView.seekTo(1); // go back to beginning
                    mVideoView.pause();
                    mPlayButton.setVisibility(View.VISIBLE);
                    mStampIndex = 0;
                    mLastPosition = 0;
                    Log.i(TAG, "removeCallbacks() from runnable");
                    mHandler.removeCallbacks(this);
                } else {
                    //mHandler.postDelayed(this, DELAY);
                }
            } else {
                if (!mStamps.isEmpty()) {
                    onPositionUpdate(mStamps);
                }
            }
        }
         mHandler.postDelayed(mRunnable, DELAY);
    };

be noted the above code will work only once expect if you make CountDownTimer or you can use Thread.sleep() with a normal loop and AsyncTask in order to not block your code because if so the application will not be responding and then your app will be crached

Thanks for your answer, and you're right, I'd like to know if it is the best practice. I am not sure I understood the last paragraph though :/ — Juliette Marquis, Oct 24 '18 at 08:31
as you mentioned you need to run the code every 40 seconds i told you this code will run one time after 40 second and then the task will be end — Basil Battikhi, Oct 24 '18 at 08:54
Doesn't the `mHandler.postDelayed(mRunnable, DELAY);` line inside the run() function make it run severak times ? Because on the tests I did, it does run several times every 40 ms until I removeCallbacks() — Juliette Marquis, Oct 24 '18 at 08:58
No postdelay will delay the code execution for a specific time thats why i told you to use Thread.sleep or countdown timer instead — Basil Battikhi, Oct 24 '18 at 09:01
Thank you for your answer, I checked it out and finally found the right configuration using postDelayed() :) — Juliette Marquis, Oct 25 '18 at 12:41

What is the correct way to use Handler and Runnable?

1 Answers1