Develop Reference

Android onScrollChanged() not being called

I am developing an android application which has a scrollview. I have overriden my view from ScrollView and have implemented the onScrollChanged method. As the scrollview scrolls and reaches the bottom, it loads more products and add them to scrollvew. I am having a strange issue. First time when products loads and I try to drag up the scrollview, onScrollChanged never happens. Then I googled and found something:
scrollView.setOnTouchListener(new ListView.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
// Disallow ScrollView to intercept touch events.
v.getParent().requestDisallowInterceptTouchEvent(false);
break;
case MotionEvent.ACTION_UP:
// Allow ScrollView to intercept touch events.
v.getParent().requestDisallowInterceptTouchEvent(true);
break;
}
// Handle ListView touch events.
v.onTouchEvent(event);
return true;
}
});
After adding this, when I try to drag the scrollview from empty area of scrollview, it starts to call onScrollChanged and afterwards I start dragging from anywhere else, onScrollChanged is being called. My question is, why it is behaving like that? It should call onScrollChanged from whatever the touch event starts. I hope, I explained my point well. Any solution?

Why don't you use endless adapter with a view like ListView or GridView to achieve the desired behavior instead

OnTouchEvent not working on child views

I have a Linear Layout that has a Button and a TextView on it. I have written a OnTouchEvent for the activity. The code works fine if I touch on the screen, but if I touch the button the code does not work. What is the possible solution for this?
public boolean onTouchEvent(MotionEvent event) {
int eventaction=event.getAction();
switch(eventaction)
{
case MotionEvent.ACTION_MOVE:
reg.setText("hey");
break;
}
return true;
}

The problem is the order of operations for how Android handles touch events. Each touch event follows the pattern of (simplified example):
Activity.dispatchTouchEvent()
ViewGroup.dispatchTouchEvent()
View.dispatchTouchEvent()
View.onTouchEvent()
ViewGroup.onTouchEvent()
Activity.onTouchEvent()
But events only follow the chain until they are consumed (meaning somebody returns true from onTouchEvent() or a listener). In the case where you just touch somewhere on the screen, nobody is interested in the event, so it flows all the way down to your code. However, in the case of a button (or other clickable View) it consumes the touch event because it is interested in it, so the flow stops at Line 4.
If you want to monitor all touches that go into your Activity, you need to override dispatchTouchEvent() since that what always gets called first, onTouchEvent() for an Activity gets called last, and only if nobody else captured the event. Be careful to not consume events here, though, or the child views will never get them and your buttons won't be clickable.
public boolean dispatchTouchEvent(MotionEvent event) {
int eventaction=event.getAction();
switch(eventaction) {
case MotionEvent.ACTION_MOVE:
reg.setText("hey");
break;
default:
break;
}
return super.dispatchTouchEvent(event);
}
Another option would be to put your touch handling code into a custom ViewGroup (like LinearLayout) and use its onInterceptTouchEvent() method to allow the parent view to steal away and handle touch events when necessary. Be careful though, as this interaction is one that cannot be undone until a new touch event begins (once you steal one event, you steal them all).
HTH

Let me add one more comment to this excellent post by #Devunwired.
If you've also set an onTouchListener on your View, then its onTouch() method will be called AFTER the dispatch methods, but BEFORE any onTouchEvent() method, i.e. in between no.3 and no.4 on #Devunwired's answer.

Try to set the descendantFocusability attribute of your layout to blocksDescendants

Activity::onTouchEvent will be called only when non of the views in the Activity WIndow consumes/handles the event. If you touch the Button, the Button will consume the events, so the Activity won't be able to handle it.
Check out following articles for more about Android Touch Event handling pipeline.
http://pierrchen.blogspot.jp/2014/03/pipeline-of-android-touch-event-handling.html

you can also try onUserInteraction():
#Override
public void onUserInteraction(){
//your code here
super.onUserInteraction();
}
works well for me!

RecyclerView list_view = findViewById(R.id.list_view);
list_view.addOnItemTouchListener(new RecyclerView.SimpleOnItemTouchListener(){
#Override
public boolean onInterceptTouchEvent(#NonNull RecyclerView rv, #NonNull MotionEvent e) {
View child = rv.findChildViewUnder(e.getX(), e.getY());
Log.i("Hello", "World");
return false;
}
});

use public boolean dispatchTouchEvent(MotionEvent event) instead on onTouchEvent()

Separate onTouchListeners for a view and its parent

I have a ListView in Android and I would like to have onTouchListeners for the row views and the parent ListView itself. I'd like to respond to single taps and long presses on the rows individually, but to flings on the ListView as a whole. (I can set the onFling method for each of the rows individually, but it's not robust, since the user can move his finger across rows.) I'm able to successfully set an onTouchListener for the rows and the ListView separately, but when I set both, the ListView listener never triggers - only the row listeners. This is the case whether I return true or false in the methods of the row listener. Does anybody know how to trigger onTouchListeners for both a view and its parent, given that they occupy the same pixels on the screen?
The relevant code for the ListView:
In the activity onCreate method:
mListViewDetector = new GestureDetector(new ListViewGestureListener());
mListViewListener = new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
return mListViewDetector.onTouchEvent(event);
}
};
mListView = getListView();
mListView.setOnTouchListener(mListViewListener);
And the custom GestureListener class (defined as a nested class in the activity):
class ListViewGestureListener extends SimpleOnGestureListener {
#Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
Log.i("ListViewGestureDetector","onFling");
return false;
}
}
The relevant code for the individual rows in the Listview:
In the bindView method of the the adapter class:
TextView textView;
textView.setOnTouchListener(new ListsTextViewOnTouchListener());
And the custom onTouchListener class (defined as a nested class in the adapter class):
class ItemsTextViewOnTouchListener implements OnTouchListener {
public boolean onTouch (View v, MotionEvent event){
switch(event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
//stuff
return false;
case MotionEvent.ACTION_CANCEL:
//stuff
return false;
default:
break;
}
return false;
}
}

Pvans,
The answer is a little tricksy, but that capability is built in. onTouchEvent() handles the TouchEvent for whichever object(s) it is a listener for. There are then two options for accomplishing what you would like.
1) You can override onInterceptTouchEvent() on the parent View and handle your fling there. I find that this works great for large Views with smaller child Views. I do not prefer this method for Lists (to be frank). onInterceptTouchEvent() is awesome at taking the Touch away from the children, but if you do this, you would have to handle both flinging left/right and scrolling horizontally.
2) You can also create a GestureDetector that is actually an invisible overlay (sort of). If you forward your onTouchEvents to it, you will still get the desired behavior, and you don't have to worry about handling your scrolling manually. In this case, you simply send the TouchEvent to the Detector and if it returns true, your List does nothing and your OnFling does the work. If it returns false, it wasn't handled so it must belong to the List or one of its children.
Hope this helps,
FuzzicalLogic

keep ontouch event when view is removed and add

I have a view in a linearlayout. When the view is longpressed the view will be removed from this linearlayout and placed, on the same position of the screen, to a relative layout. On this way a can move the view over the screen with my finger.
it almost works:
i got the longpress event working (remove the view and place the view to the relativelayout). after that i add an ontoucheventlistener so my view stays with my finger, but only for a second. the last time the touchevent is fired i got "MotionEvent.ACTION_CANCEL". When i remove my finger and place my finger again to the view i can go feature with my movement, then it will keep until i remove my finger.
I think that my problem is that the view it removed for a short moment, at that time i get a "MotionEvent.ACTION_CANCEL", however, there are still some unhandled events, they will be fired first. Thats why i got for about 1 second still ontouchevents. (this is just a thought).
someone a idee how i can keep the ontouchevent, or let the ontouchevent fired without replacing my finger?
Edited
My thought is not correct. When i do a longpress the view stays with my finger, however i lost the view as soon as i move about 50 to 100 pixels to any direction.
Edited 2
the longpress code of the view inside the linearlayout
view.setOnLongClickListener(new OnLongClickListener() {
public boolean onLongClick(View v) {
_linearLayout.removeView(v);
moveView(v);
return true;
}
});
moveView will be called by the longpress
private void moveView(View v) {
_relativeLayout.addView(v);
v.setOnTouchListener(new OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
switch(event.getAction()) {
case MotionEvent.ACTION_MOVE:
int x = (int) event.getRawX();
int y = (int) event.getRawY();
v.layout(x, y, x + v.getWidth(), y + v.getHeight());
break;
case MotionEvent.ACTION_UP:
_relativeLayout.removeView(v);
v = null;
break;
case MotionEvent.ACTION_CANCEL:
//it comes here when i move my finger more then 100 pixels
break;
}
return true;
}
});
}
of corse, this is the relevant part of the code and not the original code

Have a look at the Experience - Android Drag and Drop List post. There is also a source code that does something very similar to what are you trying to get. Eric, the author of that post, uses a separate temporary ImageView to hold a dragged view image, taken with getDrawingCache(). He also hides the original list item by setVisibility(View.INVISIBLE).
In the DragNDrop project (link above) you can replace drag(0,y) calls by drag(x,y) in DragNDrop.java to see a dragging in all directions.

Just throwing some possibilities in because I can't see the code but MotionEvent.ACTION_CANCEL could be being called as the parent layout is switched and the view is getting redrawn.
You could try overriding the onTouchEvent and at the point the ACTION_CANCEL event is sent try get hold of an equivalent view in the new layout and operate on that but I still think the better idea is to redesign so it all takes place in the same layout.

Gesture detector doesn't work with scrollable list activity

I have a simple application with two views, one is a TableView and the other is ListView. I use GestureDetector to detect the swipes across the screen similarly to how it is done here. Everything works OK, if the list view is populated with just a few items, however when the ListView fills up the whole screen the gesture detection stops working. Doing the swipe across the screen simply shows highlights one of the list items.
I think this is happening because ListView somehow steals the touch events from the GestureListener. Is there a way to prevent this?

I found that GestureDetector works fine in ListItems if you traverse a fairly accurate horizontal path. However if you stray slightly, the list scrolls and the gesture does not complete. What is going on is as follows:
The GestureDetector starts off happily taking MotionEvents from the onTouch you install in the ListItems via setOnTouchListener().
The ListView is meanwhile listening in on events sent to its child views via onInterceptTouchEvent()
The ListView detects that you have started to scroll and returns true from onInterceptTouchEvent().
From then on the MotionEvents are sent to the ListView and NOT to the original target... the ListView starts receiving MotionEvents in its onTouch handler. This continues until the final ACTION_UP. (Note that the MotionEvents from ACTION_DOWN through all the ACTION_MOVEs to ACTION_UP are considered a single gesture and everything starts again after the final ACTION_UP in the sequence)
The original target (ListItem) gets an ACTION_CANCEL MotionEvent and the GestureDetector in your ListItem bails out. This can be seen to happen if you paste the code for GestureDetector into your app and step through it.
I needed my app to behave as if the horizontal swipe continued even if the touch strays from horizontal slightly.
SOLUTION:
This involves ViewGroup.requestDisallowInterceptTouchEvent (boolean disallowIntercept) which stops the parent being able to peek at the motion events. The method involves implementing onTouchListener to detect a slight swipe (10 pixels or so) then stopping the parent intercepting motion events. The parent will then not scroll and the gesture detector continues to completion.
Here's the code:
private boolean mFlingInProgress = false;
private float mStartX = 0;
private final int FLING_TRIGGER_DISTANCE = 10;
#Override
public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
float currentX = event.getRawX();
switch (action) {
case MotionEvent.ACTION_DOWN:
mStartX = currentX;
break;
case MotionEvent.ACTION_MOVE:
if (false == mFlingInProgress) {
if (Math.abs(currentX - mStartX) > FLING_TRIGGER_DISTANCE) {
// stop the parent intercepting motion events
mLayout.getParent().requestDisallowInterceptTouchEvent(true);
mFlingInProgress = true;
}
}
break;
case MotionEvent.ACTION_UP:
mFlingInProgress = false;
break;
}
return mGestureDetector.onTouchEvent(event);
}

You could create a custom listview and then implement the gesture detector inside of this i.e. on each row of the list. Could be worth a try.