Gesture detection and ScrollView issue

Question

I'm trying to create a layout with a ViewFlipper containing ScrollViews. The idea is to detect horizontal swipes to move to previous/next ScrollView. Moreover, the ScrollView contains another ViewFlipper containing ImageView with a vertical swipe detector to go to previous/next ImageView. When I replace the ScrollView by a LinearLayout both gesture detectors work properly, but with the ScrollView, none work (the gesture listeners are not even triggers). Why does using a ScrollView disable my gesture detectors? How can I make it work?

Activity

public class ProduitHome extends Activity{        private Resources res;     float density;      private int position, parent_id;;     private int num_products;      private Produit produit;     private ImageDownloader mImageLoader;         private ViewFlipper product_viewflipper;     private ScrollView current_product_layout;     Animation next_product_out, next_product_in, previous_product_in, previous_product_out;      private GestureDetector galleryGestureDetector;     private View.OnTouchListener galleryGestureListener;      private GestureDetector productGestureDetector;     private View.OnTouchListener productGestureListener;      @Override     public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);         setContentView(R.layout.produit_home);          num_products = GlobalData.map_list_produits.get(parent_id).size();          product_viewflipper = (ViewFlipper) findViewById(R.id.product_viewflipper);          LayoutInflater inflater = getLayoutInflater();           // Add num_products view to the viewflipper          for(int i=0; i<num_products; i++){             ScrollView product_detail = (ScrollView) inflater.inflate(R.layout.produit_detail, null);             product_viewflipper.addView(product_detail);         }           // Set data and show current product          current_product_layout = (ScrollView) product_viewflipper.getChildAt(position);         product_viewflipper.setDisplayedChild(position);          setProductData();           // Set swipe listener to switch product          productGestureDetector = new GestureDetector(new ProductGestureListener());         productGestureListener = new View.OnTouchListener()          {             public boolean onTouch(View v, MotionEvent event)              {                 if (productGestureDetector.onTouchEvent(event))                  {                     return true;                 }                 else{                     return false;                 }             }         };          product_viewflipper.setOnTouchListener(productGestureListener);           // Set switch product animation          next_product_out = AnimationUtils.loadAnimation(this, R.anim.next_product_out);         next_product_in = AnimationUtils.loadAnimation(this, R.anim.next_product_in);         previous_product_in = AnimationUtils.loadAnimation(this, R.anim.previous_product_in);         previous_product_out = AnimationUtils.loadAnimation(this, R.anim.previous_product_out);      }       class VerticalSwipeListener extends SimpleOnGestureListener {          @Override         public boolean onDown(MotionEvent e) {             return true;         }          @Override         public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {              final int SWIPE_MIN_DISTANCE = 80;             final int SWIPE_MAX_OFF_PATH = 250;             final int SWIPE_THRESHOLD_VELOCITY = 200;               try {                 if (Math.abs(e1.getX() - e2.getX()) > SWIPE_MAX_OFF_PATH)                     return false;                                  ViewFlipper gallery = (ViewFlipper)current_product_layout.findViewById(R.id.product_gallery);                  if(e1.getY() - e2.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {                     gallery.showNext();                                     }  else if (e2.getY() - e1.getY() > SWIPE_MIN_DISTANCE && Math.abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {                     gallery.showPrevious();                 }                 ((RadioGroup)current_product_layout.findViewById(R.id.gallery_nav)).check(gallery.getDisplayedChild());             } catch (Exception e) {             }             return false;         }     }       class ProductGestureListener extends SimpleOnGestureListener {          @Override         public boolean onDown(MotionEvent e) {             return true;         }          @Override         public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {              final int SWIPE_MIN_DISTANCE = 120;             final int SWIPE_MAX_OFF_PATH = 250;             final int SWIPE_THRESHOLD_VELOCITY = 200;               if(!Utils.IsOnline(ProduitHome.this)){                 SRPDialogs.show(ProduitHome.this, SRPDialogs.NOT_CONNECTED);             }             else{                  try {                     if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH)                         return false;                     if(e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {                          // show next product                      }  else if (e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {                       // show previous product                      }                 } catch (Exception e) {                 }             }             return false;         }     }      public void setProductData(){          produit = GlobalData.map_produits.get(GlobalData.map_list_produits.get(parent_id).get(position).id);           TextView name = (TextView) current_product_layout.findViewById(R.id.name);         name.setText(produit.libelle);          // Load gallery          int nPics = produit.list_url_pic.size();          if(nPics>0){              ViewFlipper gallery = (ViewFlipper) current_product_layout.findViewById(R.id.product_gallery);             gallery.removeAllViews();                         mImageLoader = new ImageDownloader(res,                     ((BitmapDrawable)res.getDrawable(R.drawable.default_row_pic)).getBitmap(), 1);                        final ViewFlipper.LayoutParams params_vf = new ViewFlipper.LayoutParams(ViewFlipper.LayoutParams.FILL_PARENT, ViewFlipper.LayoutParams.FILL_PARENT);              for(String url : produit.list_url_pic){                  // Add images to viewflipper                 ImageView imageView_p = new ImageView(this);                 imageView_p.setLayoutParams(params_vf);                 imageView_p.setScaleType(ImageView.ScaleType.CENTER_CROP);                 imageView_p.setTag(url);                 imageView_p.setImageResource(R.drawable.default_row_pic);                 mImageLoader.download(url, imageView_p);                 gallery.addView(imageView_p);             }               // Swipe detector to switch picture in gallery              galleryGestureDetector = new GestureDetector(new VerticalSwipeListener());             galleryGestureListener = new View.OnTouchListener()              {                 public boolean onTouch(View v, MotionEvent event)                  {                     if (galleryGestureDetector.onTouchEvent(event))                      {                         return true;                     }                     else{                         return false;                     }                 }             };          }     } } 

Parent layout

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:id="@+id/product_home" android:layout_width="fill_parent"     android:layout_height="fill_parent" android:orientation="vertical"     android:background="@color/grey_bg">      <!-- more stuff -->      <ViewFlipper android:id="@+id/product_viewflipper"         android:layout_width="fill_parent" android:layout_height="fill_parent"         android:layout_below="@id/header_logo" />      <!-- more stuff -->  </RelativeLayout> 

ViewFlipper's children layout

<?xml version="1.0" encoding="utf-8"?> <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent" android:layout_height="fill_parent"     android:background="@color/grey_bg">      <LinearLayout android:layout_width="fill_parent"         android:layout_height="wrap_content" android:orientation="vertical"         android:gravity="center_horizontal">          <!-- more stuff -->          <RelativeLayout android:layout_below="@id/bg_content_top"             android:layout_above="@id/bg_content_bottom"             android:layout_width="300dp" android:layout_height="fill_parent"             android:background="@drawable/bg_content"             android:paddingRight="3dp" android:paddingLeft="3dp"             android:layout_centerHorizontal="true">             <!-- more stuff -->              <RelativeLayout android:id="@+id/content"                 android:layout_below="@id/title_container"                 android:layout_above="@id/bg_content_bottom"                 android:layout_width="fill_parent"                 android:layout_height="wrap_content"                 android:paddingLeft="7dp" android:paddingRight="7dp"                 android:paddingTop="10dp" android:paddingBottom="10dp">                                 <ViewFlipper android:id="@+id/product_gallery"                     android:clickable="true" android:focusable="false"                     android:layout_width="100dp" android:layout_height="150dp"                     android:layout_marginRight="10dp"                     android:layout_below="@id/title_container"                     android:layout_toRightOf="@id/gallery_nav" />                  <!-- more stuff -->              </RelativeLayout>          </RelativeLayout>          <!-- more stuff -->      </LinearLayout>  </ScrollView> 

Answer 1

I had to add

@Override public boolean dispatchTouchEvent(MotionEvent ev){     super.dispatchTouchEvent(ev);         return productGestureDetector.onTouchEvent(ev);  } 

in my Activity.

Answer 2

My answer is the same as my last one except I'm going to be more explicit.

Change

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent" android:layout_height="fill_parent"     android:background="@color/grey_bg"> 

to

<your.packagename.CustomScrollView ... etc> 

Create a class

public class CustomScrollView extends ScrollView {     private GestureDetector gestureDetector;     View.OnTouchListener gestureListener;      public CustomScrollView(Context context, AttributeSet attrs) {           super(context, attrs);           gestureDetector = new GestureDetector(new YScrollDetector());           setFadingEdgeLength(0);     }      @Override     public boolean onTouchEvent(MotionEvent ev) {         return super.onTouchEvent(ev);     }      @Override     public boolean onInterceptTouchEvent(MotionEvent ev) {         //Call super first because it does some hidden motion event handling         boolean result = super.onInterceptTouchEvent(ev);        //Now see if we are scrolling vertically with the custom gesture detector        if (gestureDetector.onTouchEvent(ev)) {             return result;        }         //If not scrolling vertically (more y than x), don't hijack the event.         else {             return false;        }     }      // Return false if we're scrolling in the x direction       class YScrollDetector extends SimpleOnGestureListener {         @Override         public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float     distanceY) {         try {             if (Math.abs(distanceY) > Math.abs(distanceX)) {                 return true;             } else {                 return false;             }         } catch (Exception e) {             // nothing         }         return false;     } } 

That code comes from the top answer here: HorizontalScrollView within ScrollView Touch Handling (So go give it a vote up if the answer is useful).

If you want to get the perpendicular direction then change

if (Math.abs(distanceY) > Math.abs(distanceX)) { 

to

if (Math.abs(distanceY) < Math.abs(distanceX)) { 

The CustomScrollView will only intercept swipes in one axis, either horizontally or vertically depending the 2 lines of code above. Since it only intercepts swipes in one axis the rest of the events will be passed to its children, now you can handle the event with your gesture/touch listener in your activity.

You will also need to change any references/casts to ScrollView to the new custom one (CustomScrollView).