Android-在片段中检索和使用视图位置

Question

I have a fragment with 4 buttons. I want to save each button's position on screen in a hash-map (each button will be mapped to its position on screen). What is the easiest way of doing it? Before using fragments, I used the onWindowFocusChanged method (in Activity) in which I could retrieve the button position. With fragments I tried to use ViewTreeObserver (with GlobalLayoutListener). Inside the anonymous class I can retrieve and save (in instance variable) the button position but outside of it these values are gone (equal 0). How can it be done?

Thanks!

EDIT: added a code snippet -

public void getViewsPosition(final ArrayList<View> viewArr) {
    for (final View v : viewArr) {
        final ViewTreeObserver vto = v.getViewTreeObserver();
        vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                int[] i = new int[2];
                v.getLocationOnScreen(i);
                _rect = new Rect(i[0], i[1], i[0] + v.getWidth(), i[1]
                        + v.getHeight());
                view_to_rect.put(v, _rect);
                if (Build.VERSION.SDK_INT < 16) {
                    vto.removeGlobalOnLayoutListener(this);
                } else {
                    vto.removeOnGlobalLayoutListener(this);
                }
            }
        });
    }
    Log.i(TAG, "size of view to rect = " + String.valueOf(view_to_rect.size()));
}

where viewArr is an arrayList of all my views in this layout ; view_to_rect is an instance variable declared as:

private static Map view_to_rect = new HashMap();

The Log always shows "size of view to rect = 0".

attached also the implementation of onViewCreated:

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    Log.i(TAG, "onViewCreated");
    final ViewGroup _mainView = (ViewGroup) getView().findViewById(
            R.id.fragment01);
    getAllViews(viewsList, _mainView);
    Log.i(TAG, "size of view list = " + String.valueOf(viewsList.size()));
    getViewsPosition(viewsList);
}

from where getViewsPosition is called.

Edit#2: I'll try to clarify my intentions. I'm building app with fragment. each fragment, let's say, has 4 buttons. I want these buttons to listen to touch events so as the user touches a button and moves his finger to another button (without lifting his finger) there will be an audio feedback of the button's name. For that I need to have all buttons positions so to be able to identify moving from one button to another (in onTouch method). And for that I need an instance variable which will keep all buttons positions on screen and I will be able to use it in onTouch. The solution you suggested does not solve the problem because outside of

public void getViewsPosition(final ArrayList viewArr)

the size of view_to_rect is still 0.

Edit #3:

Here is the process in which I try to build my collection:

1) Class signature + collection and array definition:

public class Fragment01 extends Fragment implements OnTouchListener,
    OnClickListener{
        private Map<View, Rect> view_to_rect = new HashMap<View, Rect>();
        ArrayList<View> viewsList = new ArrayList<View>();

2) onViewCreated implementation:

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    Log.i(TAG, "onViewCreated");
    final ViewGroup _mainView = (ViewGroup) getView().findViewById(
            R.id.fragment01);
    getAllViews(viewsList, _mainView);
    Log.i(TAG, "size of view list = " + String.valueOf(viewsList.size()));
    getViewsPosition(viewsList);
    Log.i(TAG, "size of view to rect = " + String.valueOf(view_to_rect.size()));
}

3) getViewsPosition(...) and onPositioUpdate() methods -

public void getViewsPosition(final ArrayList<View> viewArr) {
    for (final View v : viewArr) {
        final ViewTreeObserver vto = v.getViewTreeObserver();
        vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                int[] i = new int[2];
                v.getLocationOnScreen(i);
                _rect = new Rect(i[0], i[1], i[0] + v.getWidth(), i[1]
                        + v.getHeight());
                if (Build.VERSION.SDK_INT < 16) {
                    vto.removeGlobalOnLayoutListener(this);
                } else {
                    vto.removeOnGlobalLayoutListener(this);
                }

                onPositionUpdate();
            }
        });
    }
}

private void onPositionUpdate() {
}

The first Log in onViewCreated(...) is "size of view list = 7".

My question is how can I get the second log print out "size of view to rect = 7" ? it always returns 0.

I didn't really, probably, understand how to use your solution with onPositionUpdate() method. How should it be implemented in order to achieve my goal?

Answer 1

ViewTreeObserver will be notify only when the view is rendered, What do you you mean by

"but outside of it these values are gone"

You can just get the positions of buttons in the GlobalLayoutListener callback, and save it the instance. Remember, you can only get the positions on rendered.

REMIND:

put this code

Log.i(TAG, "size of view to rect = " + String.valueOf(view_to_rect.size()));

inside the public void onGlobalLayout() {}, then you will get non-zero.

Why:

Only the onGlobalLayout method is called, you can get non-zero.

         public void onGlobalLayout() {
                int[] i = new int[2];
                v.getLocationOnScreen(i);
                _rect = new Rect(i[0], i[1], i[0] + v.getWidth(), i[1]
                        + v.getHeight());
                view_to_rect.put(v, _rect);
                if (Build.VERSION.SDK_INT < 16) {
                    vto.removeGlobalOnLayoutListener(this);
                } else {
                    vto.removeOnGlobalLayoutListener(this);
                }

                onPositionUpdate();

            }

private void onPositionUpdate()
{
    //do your work with positions
}