Changing an image at certain time

Question

I'm working on an android studio project trying to get an image to change every half an hour, I followed an example but am having no luck; it throws no errors, it just doesen't work, here's what I have and what I've tried:

public class MainActivity extends AppCompatActivity {

long startTime = 0;
Handler feed = new Handler();
Runnable runTimer = new Runnable()
{
    @Override
    public void run() {
        Calendar now = Calendar.getInstance();
        TextView output = (TextView) findViewById(R.id.output);
        ImageView roto = (ImageView) findViewById(R.id.earthView);
        Globals g = (Globals) getApplication();
        int vision = 0;
        int visionb = 0;
        int hour = now.get(Calendar.HOUR);
        int minute = now.get(Calendar.MINUTE);
        String[] epos = g.getData56();

        if (minute >= 30) {
            visionb = 1;
        }
        if (minute < 30) {
            visionb = 0;
        }
        long millis = System.currentTimeMillis() - startTime;
        int seconds = (int) (millis / 1000);
        int minutes = seconds / 60;
        seconds = seconds % 60;
        output.setText(String.format("%d:%02d", minutes, seconds));
        vision = ((hour * 2) + visionb);
        int resID = getResources().getIdentifier(epos[vision], "drawable", getPackageName());
        if (roto != null) {
            roto.setImageResource(resID);
            feed.postDelayed(this, 500); // tried moving this around and changing the value from 0 - 3000
        }
        startTime = System.currentTimeMillis();
        feed.postDelayed(runTimer, 500); // tried moving this around and changing the value from 0 - 3000
    }
};

To test my code I put this in an onUserInteraction method and it works perfectly fine:

    @Override
    public void onUserInteraction() {
    super.onUserInteraction();
    final Globals g = (Globals) getApplication();
    Calendar now = Calendar.getInstance();
    ImageView roto = (ImageView) findViewById(R.id.earthView);
    int vision = 0;
    int visionb = 0;
    int hour = now.get(Calendar.HOUR);
    int minute = now.get(Calendar.MINUTE);
    String[] epos = g.getData56();

    if (minute >= 30) {
        visionb = 1;
    }
    if (minute < 30) {
        visionb = 0;
    }
    vision = ((hour * 2) + visionb);
    int resID = getResources().getIdentifier(epos[vision], "drawable", getPackageName());
    if (roto != null) {
        roto.setImageResource(resID);
    }
}

So I assume I'm doing something wrong, Anyone know what I'm doing wrong or missing?

Thanks for the help Landice This is the working result, giving me both a clock and every 1/2 hour of the day changes my image (which has 48 total images), again thanks for your help!

long startTime = 0;
{
final Handler feed = new Handler();
final Runnable runTimer = new Runnable() {
    @Override
    public void run() {

        Calendar now = Calendar.getInstance();
        TextView output = (TextView) findViewById(R.id.output);
        ImageView roto = (ImageView) findViewById(R.id.earthView);
        Globals g = (Globals) getApplication();
        int vision = 0;
        int visionb = 0;
        int second = now.get(Calendar.SECOND);
        int hour = now.get(Calendar.HOUR);
        int minute = now.get(Calendar.MINUTE);
        String[] epos = g.getData56();
        if (minute >= 30) {visionb = 1;}               
        if (minute < 30) {visionb = 0;}
        output.setText(String.format(hour + ":" + minute + ":" + second));
        feed.postDelayed(this, 0);
        if (minute == 30 || minute == 0) {vision = ((hour * 2) + visionb);
            int resID = getResources().getIdentifier(epos[vision], "drawable", getPackageName());
            if (roto != null) {
            roto.setImageResource(resID);
            }
        }
        startTime = System.currentTimeMillis();
    }
};
feed.postDelayed(runTimer,1000);
}

Answer 1

I think you forgot to schedule the first post. This is an example of using Handler and Runnable to schedule periodical events. This line schedules the first run.

handler.post(runTimer);

And this line inside run() schedules for the afterward events at the time it runs:

handler.postDelayed(this, 1000);

Beware of that 1000 means one second. Therefore 30 minutes will be 60*1000*30 which is 1800000 in your case.

Example:

public class MainActivity extends AppCompatActivity {

    TextView mTextView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextView = (TextView) findViewById(R.id.textview);

        final Handler handler = new Handler();
        Runnable runTimer = new Runnable()
        {
            @Override
            public void run() {
                mTextView.setText("Current Time: " + (new Date()).toString());
                handler.postDelayed(this, 1000);
            }
        };

        handler.post(runTimer);
    }
}

Also, you might want to stop the loop by removing the scheduled delayed event by:

handler.removeCallbacks(runTimer);

Answer 2

You can try this answer: How to change images in imageview every n number of seconds.

int[] imageArray = { R.drawable.image1, R.drawable.image2, R.drawable.image3, R.drawable.image4, R.drawable.image5 };

int position=0;

Timer mTimer = new Timer();