Android scrollview onScrollChanged

Question

I have a fixed content in my text view inside a scroll view. When the user scrolls to a certain position, I would like to start an activity or trigger a Toast.

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="fill_parent" android:layout_height="fill_parent"
 android:id="@+id/scroller">
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical" android:layout_width="fill_parent"
  android:layout_height="fill_parent">
  <TextView android:layout_width="fill_parent" android:id="@+id/story"
   android:layout_height="wrap_content" android:text="@string/lorem"
   android:gravity="fill" />
 </LinearLayout>
</ScrollView>

My problem is in implementing the protected method onScrollChanged to find out the position of the scroll view.

I have found this answer, is there an easier solution to this rather than declaring an interface, over ride the scrollview etc as seen on the link I posted?

you can use this http://stackoverflow.com/questions/10316743/detect-end-of-scrollview — Satria Akbar, Jun 16 '13 at 13:20

timemanx · Answer 1 · 2015-01-13T08:27:10.643

51

There is a much easier way than subclassing the ScrollView. The ViewTreeObserver object of the ScrollView can be used to listen for scrolls.

Since the ViewTreeObserver object might change during the lifetime of the ScrollView, we need to register an OnTouchListener on the ScrollView to get it's ViewTreeObserver at the time of scroll.

final ViewTreeObserver.OnScrollChangedListener onScrollChangedListener = new
                           ViewTreeObserver.OnScrollChangedListener() {

    @Override
    public void onScrollChanged() {
        //do stuff here 
    }
};

final ScrollView scrollView = (ScrollView) findViewById(R.id.scroller);
scrollView.setOnTouchListener(new View.OnTouchListener() {
    private ViewTreeObserver observer;

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        if (observer == null) {
            observer = scrollView.getViewTreeObserver();
            observer.addOnScrollChangedListener(onScrollChangedListener);
        }
        else if (!observer.isAlive()) {
            observer.removeOnScrollChangedListener(onScrollChangedListener);
            observer = scrollView.getViewTreeObserver();
            observer.addOnScrollChangedListener(onScrollChangedListener);
        }

        return false;
    }
});

edited Jan 13 '15 at 08:27

answered Jul 04 '13 at 00:20

timemanx

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1

That's not necessarily easier than subclassing `ScrollView`. It's actually more code. If you subclass you can just override the `onScrollChanged` method. – Christopher Perry Oct 02 '13 at 18:15
1

I tried this and it seems to fire the event 20 times or more for the same scroll Y value. It doesn't seem ideal. – RandomEngy Apr 01 '14 at 20:53
Well... there is a huge problem with this code! And this issue is resulting in errors like the one from @RandomEngy comment. Therefore I don't know why it got upvoted so high. It adds this listener ON EVERY TOUCH EVENT ON SCROLL. So basically if you click your scroll 20 times it will result in 20 calls to listener. The Listener should just be added once. For example like this: `scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() { @Override public void onScrollChanged() { //do stuff }});`. NOT INSIDE ON TOUCH METHOD – Bartek Lipinski Jan 12 '15 at 14:43
or even worse it will probably add AT LEAST 40 listeners (at least TOUCH_DOWN and TOUCH_UP for every click) in the example. – Bartek Lipinski Jan 12 '15 at 23:10
1

I had `OnTouchListener` because the [documentation](http://developer.android.com/reference/android/view/View.html#getViewTreeObserver%28%29) says *"The returned ViewTreeObserver observer is not guaranteed to remain valid for the lifetime of this View"*. I've edited the answer so that if the `ViewTreeObserver` isn't alive anymore, the callback to it is removed and added to `View`'s current `ViewtreeObserver`. – timemanx Jan 13 '15 at 08:43
I would suggest subclassing. That is less code and more reusable and avoids the above mentioned issues.. – Gabor Peto Jun 16 '16 at 06:29

score 15 · Accepted Answer · answered Nov 24 '10 at 03:46

15

No.

ScrollView doesn't provide a listener for scroll events or even a way to check how far down the user has scrolled, so you have to do what is suggested by the link.

answered Nov 24 '10 at 03:46

Computerish

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14

There is a method onScrollChanged that can be overridden. Likelwise getScrollX, getScrollY can be used. – Dec 10 '12 at 21:29
2

Seems this answer is invalid now. Starting from API 23 (M) there is a listener called "OnScrollChangeListener" scrollView.setOnScrollChangeListener(new View.OnScrollChangeListener() { @Override public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) { //work with parameters } }); – Chanaka Fernando Nov 28 '17 at 06:46
@S.D.NChanakaFernando It should also be noted that it still does not give a built in solution for specifics when it comes to scrolling. For example, if you want to detect the end of a scroll, you will have to do that manually using `onScrollChangeListener`, which is super annoying. Here are some suggestions of anybody stumbles over this problem: https://stackoverflow.com/questions/8181828/android-detect-when-scrollview-stops-scrolling – Benjamin Basmaci Apr 30 '19 at 07:39

Lovis · Answer 3 · 2016-12-05T10:00:24.563

10

This question is fairly old, but in case somebody drops by (like me):

Starting with API 23, Android's View has a OnScrollChangeListener and the matching setter.

The NestedScrollView from the Support library also supports setting a scroll listener even before that API level. As far as I know, NestedScrollView can be used as a replacement for the normal ScrollView without any problems.

edited Dec 05 '16 at 10:00

answered Apr 18 '16 at 15:16

Lovis

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there is no backward compatibility tho – dephinera Dec 03 '16 at 13:33
@define well, there is `NestedScrollView` in the Support lib, you csn use that insead of the regular `Scrollview` without problems – Lovis Dec 04 '16 at 21:15
Sorry, for some reason I missed the part where you mention it.. Thanks anyway – dephinera Dec 05 '16 at 09:33
@define I simply didn't mention that you can use the NestedScrollView instead of the normal one. I'll add it to the answer. – Lovis Dec 05 '16 at 09:59
1

This is great. We support API 18+ and I really wanted this stock functionality. Thanks! – the_dude_abides Jul 06 '17 at 22:19

score 8 · Answer 4 · answered Apr 16 '12 at 10:58

8

Actually there is a way to know how far the user has scrolled. The method getScrollY() from ScrollView tells you that.

answered Apr 16 '12 at 10:58

tulio84z

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Nope, according to this: http://stackoverflow.com/questions/2132370/android-listview-getscrolly-does-it-work – Timmmm Nov 09 '12 at 23:55
3

I used this solution in a project in my company. I test everything before i post something here. Maybe you should do the same? – tulio84z Nov 11 '12 at 02:08
Sorry, misread the question. It works for a `ScrollView` but not a `ListView` or a `GridView`. – Timmmm Nov 11 '12 at 14:51

score 2 · Answer 5 · answered Apr 18 '16 at 15:39

I extended my scrollView. This link may help.

class MyScroll extends ScrollView {
    boolean onTop=true;
    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        //Log.d(TAG, "scroll changed: " + this.getTop() + " "+t);
        if(t <= 0){
            onTop = true;
            //Log.d(TAG, "scroll top: " + t);
            super.onScrollChanged(l, t, oldl, oldt);
            return;
            // reaches the top end
        }
        onTop = false;

        View view = (View) getChildAt(getChildCount()-1);
        int diff = (view.getBottom()-(getHeight()+getScrollY()+view.getTop()));// Calculate the scrolldiff
        if( diff <= 0 ){
            // if diff is zero, then the bottom has been reached
        }
        super.onScrollChanged(l, t, oldl, oldt);
    }
}

Javier Amor Penas · Answer 6 · 2017-12-12T14:01:26.027

NestedScrollView is just like android.widget.ScrollView, but it supports acting as both a nested scrolling parent and child on both new and old versions of Android.

1st - Use NestedScrollView binding instead ScrollView

2nd - Set Scroll listener, like this, to detect axis Y moving for a headerView by example

    nestedScrollView.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {

        @Override
        public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
            Log.d(TAG, "onScrollChangeForY - scrollY: " + scrollY + " oldScrollY: " + oldScrollY);

            int MOVE = -1, SCROLL_UP = 0, SCROLL_DOWN = 1;
            float initialPositionY = headerView.getY();

            MOVE = scrollY > oldScrollY ? SCROLL_UP : SCROLL_DOWN;

            if (MOVE == SCROLL_UP) {

                int incrementY = scrollY - oldScrollY;

                headerView.setY(initialPositionY - incrementY);

            } else {

                int incrementY = oldScrollY - scrollY;

                headerView.setY(initialPositionY + incrementY);
            }
        }
    });

score 1 · Answer 7 · answered Mar 26 '18 at 13:21

you can use this trigger to show Toast or Start Activity

 scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
        @Override
        public void onScrollChanged() {
             // do something when Scroll  
        }
    });

score 1 · Answer 8 · answered Sep 06 '19 at 18:29

you can use this code to detect is up or down scroll

scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
            int lastScroll=0;
            @Override
            public void onScrollChanged() {
                int scrollY = scrollView.getScrollY(); // For ScrollView herzontial use getScrollX()

                if (scrollY > lastScroll ) {
                    Log.e("scroll","down scroll"+scrollY);
                } else if (scrollY < lastScroll ) {
                    Log.e("scroll","up scroll"+scrollY);
                }
                lastScroll=scrollY;
            }
        });

score 0 · Answer 9 · edited Oct 24 '17 at 06:42

0

Just use NestedScroll and NestedScroll.setOnScrollChangeListener().

edited Oct 24 '17 at 06:42

Lavekush Agrawal

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answered May 17 '17 at 21:10

Kai Wang

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score 0 · Answer 10 · answered Jun 13 '17 at 02:50

There is ready for use component, which helps to listen to scroll events of arbitrary views in Android. Internally this component adds ViewTreeObserver scroll events listener on devices with old Android API (similar as proposed in Shubhadeep Chaudhuri's answer) and View scroll events listener on devices with new Android API (API level 23+).

score -1 · Answer 11 · answered Nov 28 '17 at 06:48

Starting from API 23 Android M, you can use OnScrollChangeListener.

 scrollView.setOnScrollChangeListener(new View.OnScrollChangeListener() {
        @Override
        public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
            //work with parameters
        }
    });

Android scrollview onScrollChanged

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