Android ListView - stop scrolling at 'whole' row position

Question

Sorry for the confusing title, I cannot express the problem very concisely...

I have an Android app with a ListView that uses a circular / \"infinite\" adapter, whi

Answer 1

You can get the visible dimensions of a child using the getChildVisibleRect method. When you have that, and you get the total height of the child, you can scroll to the appropriate child.

In the example below I check whether at least half of the child is visible:

View child = lv.getChildAt (0);    // first visible child
Rect r = new Rect (0, 0, child.getWidth(), child.getHeight());     // set this initially, as required by the docs
double height = child.getHeight () * 1.0;

lv.getChildVisibleRect (child, r, null);

if (Math.abs (r.height ()) < height / 2.0) {
    // show next child
}

else {
    // show this child
}

Answer 2

My Solution:

@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)

{

    if (swipeLayout.isRefreshing()) {
        swipeLayout.setRefreshing(false);
    } else {
        int pos = firstVisibleItem;
        if (pos == 0 && lv_post_list.getAdapter().getCount()>0) {

            int topOfNext = lv_post_list.getChildAt(pos + 1).getTop();
            int heightOfFirst = lv_post_list.getChildAt(pos).getHeight();
            if (topOfNext > heightOfFirst) {
                swipeLayout.setEnabled(true);
            } else {
                swipeLayout.setEnabled(false);
            }
        }
        else
            swipeLayout.setEnabled(false);
    }
}

Answer 3

Once you know the first visible position, you should be able to use View.getLocationinWindow() or View.getLocationOnScreen() on the next position's view to get the visible height of the first. Compare that to the View's height, and scroll to the next position if appropriate.

You may need to tweak it to account for padding, depending on what your rows look like.

---

I haven't tried the above, but it seems like it should work. If it doesn't, here's another, probably less robust idea:

getLastVisiblePosition(). If you take the difference between last and first, you can see how many positions are visible on the screen. Compare that to how many positions were visible when the list was first populated(scroll position 0).

If the same number of positions are visible, simply scroll to the first visible position as you are doing. If there is one more visible, scroll to "first + 1" position.

Answer 4

Follow these 3 steps, then you can get exactly what you want!!!!

1.Initialize the two variable for scrolling up and down:

int scrollingUp=0,scrollingDown=0;

2.Then increment the value of the variable based on scrolling:

@Override
public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {

        if(mLastFirstVisibleItem<firstVisibleItem)
                {
                    scrollingDown=1;
                }
                if(mLastFirstVisibleItem>firstVisibleItem)
                {
                    scrollingUp=1;
                }
                mLastFirstVisibleItem=firstVisibleItem;
    } 

3.Then do the changes in the onScrollStateChanged():

@Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            switch (scrollState) {
            case SCROLL_STATE_IDLE:

                if(scrollingUp==1)
                {
                    mainListView.post(new Runnable() {
                        public void run() {
                            View child = mainListView.getChildAt (0);    // first visible child
                            Rect r = new Rect (0, 0, child.getWidth(), child.getHeight());     // set this initially, as required by the docs
                            double height = child.getHeight () * 1.0;
                            mainListView.getChildVisibleRect (child, r, null);
                            int dpDistance=Math.abs (r.height());
                            double minusDistance=dpDistance-height;
                            if (Math.abs (r.height()) < height/2)
                            {
                                mainListView.smoothScrollBy(dpDistance, 1500);
                            }       
                            else
                            {
                                mainListView.smoothScrollBy((int)minusDistance, 1500);
                            }
                            scrollingUp=0;

                        }
                    });
                }
                if(scrollingDown==1)
                {
                    mainListView.post(new Runnable() {
                        public void run() {

                            View child = mainListView.getChildAt (0);    // first visible child
                            Rect r = new Rect (0, 0, child.getWidth(), child.getHeight());     // set this initially, as required by the docs
                            double height = child.getHeight () * 1.0;
                            mainListView.getChildVisibleRect (child, r, null);
                            int dpDistance=Math.abs (r.height());
                            double minusDistance=dpDistance-height;
                            if (Math.abs (r.height()) < height/2)
                            {
                                mainListView.smoothScrollBy(dpDistance, 1500);
                            }       
                            else
                            {
                                mainListView.smoothScrollBy((int)minusDistance, 1500);
                            }
                            scrollingDown=0;
                        } 
                    });
                }
            break;
            case SCROLL_STATE_TOUCH_SCROLL:

                break;
                }
            }

Answer 5

If you can get the position of the row that needs to be scrolled to, you can use the method:

smoothScrollToPosition

So something like:

int pos = lv.getFirstVisiblePosition();
lv.smoothScrollToPosition(pos);

Edit
Try this, sorry I don't have time to test, I'm out and about.

ImageView iv = //Code to find the image view
Rect rect = new Rect(iv.getLeft(), iv.getTop(), iv.getRight(), iv.getBottom());
lv.requestChildRectangleOnScreen(lv, rect, false);

Answer 6

Here's my final code inspired by Shade's answer.

I forgot to add "if(Math.abs(r.height())!=height)" at first. Then it just scrolls twice after it scroll to correct position because it's always greater than height/2 of childView. Hope it helps.

listView.setOnScrollListener(new AbsListView.OnScrollListener(){

            @Override
            public void onScrollStateChanged(AbsListView view,int scrollState) {
                if (scrollState == SCROLL_STATE_IDLE){
                    View child = listView.getChildAt (0);    // first visible child
                    Rect r = new Rect (0, 0, child.getWidth(), child.getHeight());     // set this initially, as required by the docs
                    double height = child.getHeight () * 1.0;
                    listView.getChildVisibleRect (child, r, null);
                    if(Math.abs(r.height())!=height){//only smooth scroll when not scroll to correct position
                        if (Math.abs (r.height ()) < height / 2.0) {
                            listView.smoothScrollToPosition(listView.getLastVisiblePosition());
                        }
                        else if(Math.abs (r.height ()) > height / 2.0){
                            listView.smoothScrollToPosition(listView.getFirstVisiblePosition());
                        }
                        else{
                            listView.smoothScrollToPosition(listView.getFirstVisiblePosition());
                        }

                    }
                }
            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {

            }});