Android: Example Fragment communication via interfaces with parents, and informing children Fragments of updates depending on their state.

ImageSelectorFragment.onImageSelected().java

@Override
public void onImageSelected(ImageItem imageItem, int position) {

    // Only inform the other fragments if the selected position is new
    if (mCurImagePosition != position) {

        Log.d(TAG, "onImageSelected: title = " + imageItem.getTitle() + " position = " + position);

        // Keep track of the selected image
        mCurImageResourceId = imageItem.getImageResId();
        mCurImagePosition = position;

        // Get the fragment manager for this fragment's children
        FragmentManager fragmentManager = getChildFragmentManager();
        ImageListFragment imageListFragment = (ImageListFragment) fragmentManager.findFragmentByTag(ImageListFragment.class.getName());
        ImagePagerFragment imagePagerFragment = (ImagePagerFragment) fragmentManager.findFragmentByTag(ImagePagerFragment.class.getName());
        
        // If the fragments are in the current layout, have them select the
        // current image
        if (imageListFragment != null) {
            imageListFragment.setImageSelected(imageItem, position);
        }
        if (imagePagerFragment != null) {
            imagePagerFragment.setImageSelected(imageItem, position);
        }
        
        // Notify the parent listener that an image was selected
        if (mParentOnImageSelectedListener != null) {
            mParentOnImageSelectedListener.onImageSelected(imageItem, position);
        }

    }
}

OnImageSelectedListener.java

public interface OnImageSelectedListener {
    
    /**
     * Inform the listener that an image has been selected.
     * 
     * @param imageItem
     * @param position
     */
    public void onImageSelected(ImageItem imageItem, int position);
}