[android] Detect end of ScrollView

I have an app, that has an Activity that uses a ScrollView. I need to detect when user gets to the bottom of the ScrollView. I did some googleing and I found this page where is explained. But, in the example, that guys extends ScrollView. As I said, I need to extend Activity.

So, I said "ok, let's try to make a custom class extending ScrollView, override the onScrollChanged() method, detect the end of the scroll, and act accordingly".

I did, but in this line:

scroll = (ScrollViewExt) findViewById(R.id.scrollView1);

it throws a java.lang.ClassCastException. I changed the <ScrollView> tags in my XML but, obviously, it doesn't work. My questions are: Why, if ScrollViewExt extends ScrollView, throws to my face a ClassCastException? is there any way to detect end of scrolling without messing too much?

Thank you people.

EDIT: As promised, here is the piece of my XML that matters:

<ScrollView
        android:id="@+id/scrollView1"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >


        <WebView
            android:id="@+id/textterms"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center_horizontal"
            android:textColor="@android:color/black" />

    </ScrollView>

I changed it from TextView to WebView to be able of justifying the text inside. What i want to achieve is the "Accept button doesn't activate until the terms of the contract are fully read" thing. My extended class is called ScrollViewExt. If i change the tag ScrollView for ScrollViewExt it throws an

android.view.InflateException: Binary XML file line #44: Error inflating class ScrollViewExt

because it doesn't understand the tag ScrollViewEx. I don't think it has a solution...

Thanks for your answers!

I wanted to show/hide a FAB with an offset before the very bottom of the scrollview. This is the solution I came up with (Kotlin):

scrollview.viewTreeObserver.addOnScrollChangedListener {
    if (scrollview.scrollY < scrollview.getChildAt(0).bottom - scrollview.height - offset) {
        // fab.hide()
    } else {
        // fab.show()
    }
}

Fustigador answer was great, but I found some device (Like Samsung Galaxy Note V) cannot reach 0, have 2 point left, after the calculation. I suggest to add a little buffer like below:

@Override
public void onScrollChanged(ScrollViewExt scrollView, int x, int y, int oldx, int oldy) {
    // We take the last son in the scrollview
    View view = (View) scrollView.getChildAt(scrollView.getChildCount() - 1);
    int diff = (view.getBottom() - (scrollView.getHeight() + scrollView.getScrollY()));

    // if diff is zero, then the bottom has been reached
    if (diff <= 10) {
        // do stuff
    }
}

scrollView = (ScrollView) findViewById(R.id.scrollView);

    scrollView.getViewTreeObserver()
            .addOnScrollChangedListener(new 
            ViewTreeObserver.OnScrollChangedListener() {
                @Override
                public void onScrollChanged() {

                    if (!scrollView.canScrollVertically(1)) {
                        // bottom of scroll view
                    }
                    if (!scrollView.canScrollVertically(-1)) {
                        // top of scroll view


                    }
                }
            });

I went through the solutions on the internet. Mostly solutions didn't work in the project I'm working on. Following solutions work fine for me.

Using onScrollChangeListener (works on API 23):

   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        scrollView.setOnScrollChangeListener(new View.OnScrollChangeListener() {
            @Override
            public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {

                int bottom =   (scrollView.getChildAt(scrollView.getChildCount() - 1)).getHeight()-scrollView.getHeight()-scrollY;

                if(scrollY==0){
                    //top detected
                }
                if(bottom==0){
                    //bottom detected
                }
            }
        });
    }

using scrollChangeListener on TreeObserver

 scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
        @Override
        public void onScrollChanged() {
            int bottom =   (scrollView.getChildAt(scrollView.getChildCount() - 1)).getHeight()-scrollView.getHeight()-scrollView.getScrollY();

            if(scrollView.getScrollY()==0){
                //top detected
            }
            if(bottom==0) {
                //bottom detected
            }
        }
    });

Hope this solution helps :)

Most of answers works beside a fact, that when u scroll to the bottom, listener is triggered several times, which in my case is undesirable. To avoid this behavior I've added flag scrollPositionChanged that checks if scroll position even changed before calling method once again.

public class EndDetectingScrollView extends ScrollView {
    private boolean scrollPositionChanged = true;

    private ScrollEndingListener scrollEndingListener;

    public interface ScrollEndingListener {
        void onScrolledToEnd();
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);

        View view = this.getChildAt(this.getChildCount() - 1);
        int diff = (view.getBottom() - (this.getHeight() + this.getScrollY()));
        if (diff <= 0) {
            if (scrollPositionChanged) {
                scrollPositionChanged = false;
                if (scrollEndingListener != null) {
                    scrollEndingListener.onScrolledToEnd();
                }
            }
        } else {
            scrollPositionChanged = true;
        }
    }

    public void setScrollEndingListener(ScrollEndingListener scrollEndingListener) {
        this.scrollEndingListener = scrollEndingListener;
    }
}

Then just set listener

scrollView.setScrollEndingListener(new EndDetectingScrollView.ScrollEndingListener() {
    @Override
    public void onScrolledToEnd() {
        //do your stuff here    
    }
});

You may do the same thing if u do in like

scrollView.getViewTreeObserver().addOnScrollChangedListener(...)

but you have to provide flag from class your adding this listener.

All of these answers are so complicated, but there is a simple built-in method that accomplishes this: canScrollVertically(int)

For example:

@Override
public void onScrollChanged() {
    if (!scrollView.canScrollVertically(1)) {
        // bottom of scroll view
    }
    if (!scrollView.canScrollVertically(-1)) {
        // top of scroll view
    }
}

This also works with RecyclerView, ListView, and actually any other view since the method is implemented on View.

If you have a horizontal ScrollView, the same can be achieved with canScrollHorizontally(int)

We should always add scrollView.getPaddingBottom() to match full scrollview height because some time scroll view has padding in xml file so that case its not going to work.

scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
        @Override
        public void onScrollChanged() {
            if (scrollView != null) {
               View view = scrollView.getChildAt(scrollView.getChildCount()-1);
               int diff = (view.getBottom()+scrollView.getPaddingBottom()-(scrollView.getHeight()+scrollView.getScrollY()));

          // if diff is zero, then the bottom has been reached
               if (diff == 0) {
               // do stuff
                }
            }
        }
    });

To determine if you are at the end of your custom ScrollView you could also use a member variable and store the last y-position. Then you can compare the last y-position with the current scroll position.

private int scrollViewPos;

...

@Override
public void onScrollChanged(ScrollViewExt scrollView, int x, int y, int oldx, int oldy) {

   //reached end of scrollview
   if (y > 0 && scrollViewPos == y){
      //do something
   }

   scrollViewPos = y;
}

EDIT

With the content of your XML, I can see that you use a ScrollView. If you want to use your custom view, you must write com.your.packagename.ScrollViewExt and you will be able to use it in your code.

<com.your.packagename.ScrollViewExt
    android:id="@+id/scrollView1"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <WebView
        android:id="@+id/textterms"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center_horizontal"
        android:textColor="@android:color/black" />

</com.your.packagename.ScrollViewExt>

EDIT END

Could you post the xml content ?

I think that you could simply add a scroll listener and check if the last item showed is the lastest one from the listview like :

mListView.setOnScrollListener(new OnScrollListener() {      
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub      
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        // TODO Auto-generated method stub
        if(view.getLastVisiblePosition()==(totalItemCount-1)){
            //dosomething
        }
    }
});

You can make use of the Support Library's NestedScrollView and it's NestedScrollView.OnScrollChangeListener interface.

https://developer.android.com/reference/android/support/v4/widget/NestedScrollView.html

Alternatively if your app is targeting API 23 or above, you can make use of the following method on the ScrollView:

View.setOnScrollChangeListener(OnScrollChangeListener listener) 

Then follow the example that @Fustigador described in his answer. Note however that as @Will described, you should consider adding a small buffer in case the user or system isn't able to reach the complete bottom of the list for any reason.

Also worth noting is that the scroll change listener will sometimes be called with negative values or values greater than the view height. Presumably these values represent the 'momentum' of the scroll action. However unless handled appropriately (floor / abs) they can cause problems detecting the scroll direction when the view is scrolled to the top or bottom of the range.

https://developer.android.com/reference/android/view/View.html#setOnScrollChangeListener(android.view.View.OnScrollChangeListener)

I found a simple way to detect this :

   scrollView.getViewTreeObserver()
       .addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
            @Override
            public void onScrollChanged() {
                if (scrollView.getChildAt(0).getBottom()
                     <= (scrollView.getHeight() + scrollView.getScrollY())) {
                    //scroll view is at bottom
                } else {
                    //scroll view is not at bottom
                }
            }
        });

• Doesn't need to custom ScrollView.
• Scrollview can host only one direct child, so scrollView.getChildAt(0) is okay.
• This solution is right even the height of direct child of scroll view is match_parent or wrap_content.