ScrollView and Gallery interfering

Question

hello

I have a Gallery composed of many ScrollViews each of which occupies the whole screen. problem is the ScrollViews' onTouchEvent returns true and therefore prevent any other view in the DOM to handle the same event (which is swallowed after being processed at the ScrollView level). As a result the Gallery doesn't scroll anymore. On the other hand if I override onTouchEvent like this:

   @Override
   public boolean onTouchEvent(MotionEvent ev) {
      super.onTouchEvent(ev);
      return false; // <<<<<<<<<<<<<<<<<
   }   

then the Gallery receives its on event to process but the SrollView doesnt scroll anymore. Either way you lose! or do you?

problem sounds puzzling but I am sure if u stumbled upon it in the past u r gonna recognize it straight away as it a freaking damn one!

thanks

Answer 1

I wrote this custom class to be able to deal with that problem, and so far it seems to be a decent solution. It's not perfect and I haven't stuck a fork in it to call it done, but hopefully this may be of some use to someone :-)

import android.content.Context;
import android.view.MotionEvent;
import android.widget.Gallery;
import android.widget.ScrollView;

public class GalleryFriendlyScrollView extends ScrollView{

    private static int NONE = -1;
    private static int DOSCROLLVIEW = 0;
    private static int DOGALLERY = 1;

    private float lastx = 0;
    private float lasty = 0;
    private float firstx = 0;
    private float firsty = 0;
    private float lastRawx = 0;
    private float lastRawy = 0;
    private int gestureRecipient = NONE;
    private boolean donewithclick = true;
    private Gallery parent = null;
    private boolean firstclick = true;

    public GalleryFriendlyScrollView(Context context) {
        super(context);
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        boolean retthis = true;
        //Indicating a fresh click
        if(donewithclick){
            firstx = ev.getX();
            firsty = ev.getY();
            lastx = firstx;
            lasty = firsty;
            lastRawx = ev.getRawX();
            lastRawy = ev.getRawY();
            donewithclick = false;
            firstclick = true;
        }
        //We don't know where these gesture events are supposed to go to. 
        //We have movement on the x and/or why axes, so we can determine where they should go now.
        if((gestureRecipient == NONE) && (lastx != ev.getX() || lasty != ev.getY())){
            //Determine whether there's more movement vertically or horizontally
            float xdiff = ev.getX() - lastx;
            float ydiff = ev.getY() - lasty;
            if(xdiff < 0)xdiff = xdiff * -1;
            if(ydiff < 0)ydiff = ydiff * -1;
            if((xdiff) > (ydiff)){
                gestureRecipient = DOGALLERY;
            } else {
                gestureRecipient = DOSCROLLVIEW;
            }
        }
        if(gestureRecipient == DOGALLERY){
            if(!firstclick){
                //After you drag the screen left or right a bit, the baseline for where it calculates
                //x and y from changes, so we need to adjust the offset to our original baseline
                float offsetx = (((ev.getX() - lastx) - (ev.getRawX() - lastRawx)) * -1);
                float offsety = (((ev.getY() - lasty) - (ev.getRawY() - lastRawy)) * -1);
                ev.offsetLocation(offsetx, offsety);
            }
            retthis = getGallery().onTouchEvent(ev);
            firstclick = false;
        } else if(gestureRecipient == DOSCROLLVIEW){
            retthis = super.onTouchEvent(ev);
        }
        if(ev.getAction() == MotionEvent.ACTION_UP){
            //User's finger has been lifted
            if(((firstx == ev.getX()) && (firsty == ev.getY()))){
                //Since there isn't any movement in either direction, it's a click
                getGallery().onSingleTapUp(ev);
                super.onTouchEvent(ev);
            }
            donewithclick = true;
            gestureRecipient = NONE;
        }
        //And record our coordinate data
        lastx = ev.getX();
        lasty = ev.getY();
        lastRawx = ev.getRawX();
        lastRawy = ev.getRawY();
        return retthis;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        getGallery().onTouchEvent(ev);
        return super.onInterceptTouchEvent(ev);
    }

    private Gallery getGallery(){
        //Gets the gallery, in this case assuming the ScrollView is the direct child in the gallery.
        //Adjust as needed
        if(parent == null){
            parent = (Gallery) this.getParent();
        }
        return parent;
    }
}

I'd love to hear of people's experiences with this, and any suggestions you have.