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?

Solution 1

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.

Solution 2

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;
    }
});

Solution 3

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.

Solution 4

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

Solution 5

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;
            }
        });

View more solutions

Comments

[Satria Akbar]

you can use this stackoverflow.com/questions/10316743/detect-end-of-scrollvie‌​w

[Timmmm]

Nope, according to this: stackoverflow.com/questions/2132370/…

[tulio84z]

I used this solution in a project in my company. I test everything before i post something here. Maybe you should do the same?

[Timmmm]

Sorry, misread the question. It works for a ScrollView but not a ListView or a GridView.

[Admin]

There is a method onScrollChanged that can be overridden. Likelwise getScrollX, getScrollY can be used.

[Christopher Perry]

That's not necessarily easier than subclassing ScrollView. It's actually more code. If you subclass you can just override the onScrollChanged method.

[RandomEngy]

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.

[Bartek Lipinski]

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]

or even worse it will probably add AT LEAST 40 listeners (at least TOUCH_DOWN and TOUCH_UP for every click) in the example.

[timemanx]

I had OnTouchListener because the documentation 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.

[Gabor Peto]

I would suggest subclassing. That is less code and more reusable and avoids the above mentioned issues..

[dephinera]

there is no backward compatibility tho

[Lovis]

@define well, there is NestedScrollView in the Support lib, you csn use that insead of the regular Scrollview without problems

[dephinera]

Sorry, for some reason I missed the part where you mention it.. Thanks anyway

[Lovis]

@define I simply didn't mention that you can use the NestedScrollView instead of the normal one. I'll add it to the answer.

[the_dude_abides]

This is great. We support API 18+ and I really wanted this stock functionality. Thanks!

[Chanaka Fernando]

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 } });

[Benjamin Basmaci]

@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: stackoverflow.com/questions/8181828/…