Android Open Source - ShowMeTweets Endless Scroll Listener

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Back to project page ShowMeTweets.

License

The source code is released under:

MIT License

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Java Source Code

package com.fcduarte.showmetweets.listeners;
/*from w  w  w. j  a v a  2  s.  c om*/
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;

public abstract class EndlessScrollListener implements 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
  }
}

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