Android camera: stopPreview vs releaseCamera

Question

I am making an application where I have a camera inside of a viewPager. I am wondering what would best be suited to "pause" and "resume" the camera so it doesn't hog resources when it is pre-loaded. I have the feeling that stopPreview is better suited for this as it does not release the camera but keeps it however it doesn't display the camera which is the main reason it hogs resources.

• Enter & exit application: startCamera() & releaseCamera()
• Tab visible & not visible: startPreview() & stop Preview()

Would this be a good rule of thumb?

Answer 1

I had a similar situation. :

If I kept camera (in ViewPager) in on state, the swipe were clunky and OOM exceptions were frequent.

Two options came in my mind:

shift the entire instance in a different thread

OR

use stopPreview() and startPreview()

I went with the second one :

However, instead of doing this on Fragment lifecycle callbacks I gave a button on the fragment which toggled the preview. Reason being, if user is swiping very fast, you can still receive OOm exception since the preview calls will be queued, especially if there are very few fragments in the viewPager.

In essence Release camera onPause(), acquire camera in onResume() and give a groovy button in fragment which will toggle your Preview on the surface!

Answer 2

Hello Karl I had the same things need to implement in view pager. I have circular viewer in which one fragment has the camera fragment. I want to handle the camera preview in such a way so it should not consume the camera resource.

As you know android view pager default load two fragment in to the memory. We implemented the view pager change listener and call the fragment method to start and stop the preview. even also destroy the camera preview in on destroy method of fragment.

class ViewPagerChangeListener implements ViewPager.OnPageChangeListener {

        int currentPosition = DEFAULT_FRAGMENT;

        @Override
        public void onPageScrollStateChanged(int state) {
            TimberLogger.d(TAG, "onPageScrollStateChanged");
        }

        @Override
        public void onPageScrolled(int index, float arg1, int arg2) {
            TimberLogger.d(TAG, "onPageScrolled" + index);
        }

        @Override
        public void onPageSelected(int position) {
            mWatchPosition = position;
            TimberLogger.d(TAG, "onPageSelected" + mWatchPosition);

            int newPosition = 0;
            if (position > 4) {
                newPosition = position;
            }

            TimberLogger.d(TAG, "newPosition" + newPosition);

            /**
             * Listener knows the new position and can call the interface method
             * on new Fragment with the help of PagerAdapter. We can here call
             * onResumeFragment() for new fragment and onPauseFragment() on the
             * current one.
             */

            // new fragment onResume
            loadedFragment(newPosition).onResumeFragment();

            // current fragment onPuase called
            loadedFragment(currentPosition).onPauseFragment();

            currentPosition = newPosition;

            TimberLogger.d(TAG, "currentPosition" + currentPosition);
        }
    }

See the two method onResumeFragment and onPuaseFragment this two are the custom function each view pager fragment implements. In view pager change event we call the pause of current fragment and onResume of the new fragment.

// new fragment onResume
 loadedFragment(newPosition).onResumeFragment();

 // current fragment onPuase called
 loadedFragment(currentPosition).onPauseFragment();

You can write your camera start preview inside custom method onResumeFragment and stop preview in onPauseFragment and also make sure you should override the onDestory() method of your camera fragment for release the camera resources.