androidinfinite-scrollendlessscroll

Android: Infinite Scroll to TOP in listview


I'm trying to implement an endless scrolling to top where I would load more data when the user is getting close to the top of the listview (like in a messenger app). I have a scroll to bottom class which works fine, but I don't manage to find a library or modify this code to detect the scroll to top. Could anybody help?

Here is the class :

public abstract class EndlessScrollListener implements AbsListView.OnScrollListener {
    // The minimum amount of items to have below your current scroll position
    // before loading more.
    private int visibleThreshold = 5;
    // The current offset index of data you have loaded
    private int currentPage = 0;
    // The total number of items in the dataset after the last load
    private int previousTotalItemCount = 0;
    // True if we are still waiting for the last set of data to load.
    private boolean loading = true;
    // Sets the starting page index
    private int startingPageIndex = 0;

    public EndlessScrollListener() {
    }

    public EndlessScrollListener(int visibleThreshold) {
        this.visibleThreshold = visibleThreshold;
    }

    public EndlessScrollListener(int visibleThreshold, int startPage) {
        this.visibleThreshold = visibleThreshold;
        this.startingPageIndex = startPage;
        this.currentPage = startPage;
    }

    // This happens many times a second during a scroll, so be wary of the code you place here.
    // We are given a few useful parameters to help us work out if we need to load some more data,
    // but first we check if we are waiting for the previous load to finish.
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
    {
        // If the total item count is zero and the previous isn't, assume the
        // list is invalidated and should be reset back to initial state
        if (totalItemCount < previousTotalItemCount) {
            this.currentPage = this.startingPageIndex;
            this.previousTotalItemCount = totalItemCount;
            if (totalItemCount == 0) { this.loading = true; }
        }
        // If it’s still loading, we check to see if the dataset count has
        // changed, if so we conclude it has finished loading and update the current page
        // number and total item count.
        if (loading && (totalItemCount > previousTotalItemCount)) {
            loading = false;
            previousTotalItemCount = totalItemCount;
            currentPage++;
        }

        // If it isn’t currently loading, we check to see if we have breached
        // the visibleThreshold and need to reload more data.
        // If we do need to reload some more data, we execute onLoadMore to fetch the data.
        if (!loading && (totalItemCount - visibleItemCount)<=(firstVisibleItem + visibleThreshold)) {
            onLoadMore(currentPage + 1, totalItemCount);
            loading = true;
        }
    }

    // Defines the process for actually loading more data based on page
    public abstract void onLoadMore(int page, int totalItemsCount);

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // Don't take any action on changed
    }
}

Solution

  • I made some modification to your class, adding a parameter to decide the direction setScrollDirection by default it will be SCROLL_DIRECTION_DOWN please test it and let me know how it works :)

    public abstract class EndlessScrollListener implements AbsListView.OnScrollListener {
    
        public final static int SCROLL_DIRECTION_UP = 0;
        public final static int SCROLL_DIRECTION_DOWN = 1;
    
        // The minimum amount of items to have below your current scroll position
        // before loading more.
        private int visibleThreshold = 5;
        // The current offset index of data you have loaded
        private int currentPage = 0;
        // The total number of items in the dataset after the last load
        private int previousTotalItemCount = 0;
    
        // True if we are still waiting for the last set of data to load.
        private boolean loading = true;
        // Sets the starting page index
        private int startingPageIndex = 0;
    
        private int scrollDirection = SCROLL_DIRECTION_DOWN;
    
        public EndlessScrollListener() {
        }
    
        public EndlessScrollListener(int visibleThreshold) {
            this.visibleThreshold = visibleThreshold;
        }
    
        public EndlessScrollListener(int visibleThreshold, int startPage) {
            this.visibleThreshold = visibleThreshold;
            this.startingPageIndex = startPage;
            this.currentPage = startPage;
        }
    
        // This happens many times a second during a scroll, so be wary of the code you place here.
        // We are given a few useful parameters to help us work out if we need to load some more data,
        // but first we check if we are waiting for the previous load to finish.
        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
        {
            Log.v("EndlessScroll", "firstVisibleItem: "+firstVisibleItem);
            Log.v("EndlessScroll", "visibleItemCount: "+visibleItemCount);
            Log.v("EndlessScroll", "totalItemCount: "+totalItemCount);
            // If the total item count is zero and the previous isn't, assume the
            // list is invalidated and should be reset back to initial state
            if (totalItemCount < previousTotalItemCount) {
                this.currentPage = this.startingPageIndex;
                this.previousTotalItemCount = totalItemCount;
                if (totalItemCount == 0) { this.loading = true; }
            }
            // If it’s still loading, we check to see if the dataset count has
            // changed, if so we conclude it has finished loading and update the current page
            // number and total item count.
            if (loading && (totalItemCount > previousTotalItemCount)) {
                loading = false;
                previousTotalItemCount = totalItemCount;
                currentPage++;
            }
    
            // If it isn’t currently loading, we check to see if we have breached
            // the visibleThreshold and need to reload more data.
            // If we do need to reload some more data, we execute onLoadMore to fetch the data.
            if (!loading)
            {
                if( scrollDirection == SCROLL_DIRECTION_DOWN && (totalItemCount - visibleItemCount)<=(firstVisibleItem + visibleThreshold)) {
                    onLoadMore(currentPage + 1, totalItemCount);
                    loading = true;
                }
                else if( scrollDirection == SCROLL_DIRECTION_UP && firstVisibleItem<=visibleThreshold) {
                    onLoadMore(currentPage + 1, totalItemCount);
                    loading = true;
                }
            }
        }
    
        // Defines the process for actually loading more data based on page
        public abstract void onLoadMore(int page, int totalItemsCount);
    
        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            // Don't take any action on changed
        }
    
        public int getScrollDirection() {
            return scrollDirection;
        }
    
        public void setScrollDirection(int scrollDirection) {
            if (scrollDirection == SCROLL_DIRECTION_DOWN || scrollDirection == SCROLL_DIRECTION_UP)
            { this.scrollDirection = scrollDirection; }
        }
    
        public boolean isLoading() {
            return loading;
        }
    
        public void finishedLoading() {
            this.loading = false;
        }
    
    }