Android开源中国客户端学习 上拉刷新 底部加载 的listview <4>

此次学习一些osc客户端的 上拉刷新 底部加载 的listview 这里仍是以加载新闻为例

 osc上的下拉刷新 和底部自动加载下一页是和qq空间等app类似的，那就学习一下

其实osc是使用了一个开源的控件 --PullToRefreshListView

具体代码恕不粘贴

具体的使用在fragme_news.xml中

<net.oschina.app.widget.PullToRefreshListView
        android:id="@+id/frame_listview_news"
        style="@style/widget_listview" />

在这里说一点，其实osc各个功能的切换只不过是 切换四个fragmelayout的可见性。具体请查看main.xml

先说下拉刷新,其实使用了PullToRefreshListView这个控件后,使用下拉就很简单了 只需监听一个下来事件就ok'

lvNews.setOnRefreshListener(new PullToRefreshListView.OnRefreshListener() {
			public void onRefresh() {
				loadLvNewsData(curNewsCatalog, 0, lvNewsHandler,
						UIHelper.LISTVIEW_ACTION_REFRESH);
			}
		});

只要下拉到必定程度后就可触发这个事件了,而后就loadLvNewsData方法载入数据了,咱们再看一下最后一个参数,在调用loadLvNewsData这里就会 isRefresh = true; 

ok 既然isRefresh= true 了 那么无论是否有缓存可读都会从网络读取数据到listview

在news的handler中可能还须要出来上次刷新时间 在获取handler的构造函数handleMessage中:

if (msg.arg1 == UIHelper.LISTVIEW_ACTION_REFRESH) {
					lv.onRefreshComplete(getString(R.string.pull_to_refresh_update)
							+ new Date().toLocaleString());
					lv.setSelection(0);
				} else if (msg.arg1 == UIHelper.LISTVIEW_ACTION_CHANGE_CATALOG) {//是否显示上次何时刷新
					lv.onRefreshComplete();
					lv.setSelection(0);
				}

而后是滑动到底部 显示progressbar并加载下一页数据

其实就是控制listview的footview的显示状态:当listview滑动到最底部时,把footview由"更多"改为progressbar 并显示"加载中..."

lvNews.addFooterView(lvNews_footer);// 添加底部视图 必须在setAdapter前 添加FootView

看看底部加载的核心代码:

lvNews.setOnScrollListener(new AbsListView.OnScrollListener() {
			public void onScrollStateChanged(AbsListView view, int scrollState) {
				lvNews.onScrollStateChanged(view, scrollState);

				// 数据为空--不用继续下面代码了
				if (lvNewsData.isEmpty())
					return;

				// 判断是否滚动到底部
				boolean scrollEnd = false;
				try {
					if (view.getPositionForView(lvNews_footer) == view
							.getLastVisiblePosition())// judge if the last view on screen is thelvNews_footer

						scrollEnd = true;
				} catch (Exception e) {
					scrollEnd = false;
				}

				int lvDataState = StringUtils.toInt(lvNews.getTag());
				if (scrollEnd && lvDataState == UIHelper.LISTVIEW_DATA_MORE) {
					lvNews.setTag(UIHelper.LISTVIEW_DATA_LOADING);// prevent repeat load
					lvNews_foot_more.setText(R.string.load_ing);
					lvNews_foot_progress.setVisibility(View.VISIBLE);
					// 当前pageIndex lvNewsSumData: the current count the app has load the news.
					int pageIndex = lvNewsSumData / AppContext.PAGE_SIZE;
					loadLvNewsData(curNewsCatalog, pageIndex, lvNewsHandler,
							UIHelper.LISTVIEW_ACTION_SCROLL);
				}
			}

那么就分析一下

首先判断是否滑动到底部

// 判断是否滚动到底部
				boolean scrollEnd = false;
				try {
					if (view.getPositionForView(lvNews_footer) == view
							.getLastVisiblePosition())// judge if the last view on screen is thelvNews_footer

						scrollEnd = true;
				} catch (Exception e) {
					scrollEnd = false;
				}

感受用try 块 作判断是否到底部不是什么好方法,会不会很耗费资源?若是是scrollEnd = true

int lvDataState = StringUtils.toInt(lvNews.getTag());
				if (scrollEnd && lvDataState == UIHelper.LISTVIEW_DATA_MORE) {
					lvNews.setTag(UIHelper.LISTVIEW_DATA_LOADING);// prevent repeat load
					lvNews_foot_more.setText(R.string.load_ing);
					lvNews_foot_progress.setVisibility(View.VISIBLE);
					// 当前pageIndex lvNewsSumData: the current count the app has load the news.
					int pageIndex = lvNewsSumData / AppContext.PAGE_SIZE;
					loadLvNewsData(curNewsCatalog, pageIndex, lvNewsHandler,
							UIHelper.LISTVIEW_ACTION_SCROLL);
				}

注意这里有一个

int lvDataState = StringUtils.toInt(lvNews.getTag());和判断lvDataState == UIHelper.LISTVIEW_DATA_MORE这是为了防止重复加载load 数据的.

OK 如今就开始使用loadLvNewsData函数load数据了,那何时把progressbar消失呢?固然是在载入完了了数据以后,那么根据第一篇文章咱们知道确定是在handler中处理了

其实实在初始化的时候

lvNewsHandler = this.getLvHandler(lvNews, lvNewsAdapter,
				lvNews_foot_more, lvNews_foot_progress, AppContext.PAGE_SIZE);

这里lvNews_foot_more, lvNews_foot_progress,两个参数就分别是footerview的两个控件了

if (msg.what < pageSize) {
						lv.setTag(UIHelper.LISTVIEW_DATA_FULL);
						adapter.notifyDataSetChanged();
						more.setText(R.string.load_full);
					} else if (msg.what == pageSize) {
						lv.setTag(UIHelper.LISTVIEW_DATA_MORE);
						adapter.notifyDataSetChanged();
						more.setText(R.string.load_more);

						// 特殊处理-热门动弹不能翻页
						if (lv == lvTweet) {
							TweetList tlist = (TweetList) msg.obj;
							if (lvTweetData.size() == tlist.getTweetCount()) {
								lv.setTag(UIHelper.LISTVIEW_DATA_FULL);
								more.setText(R.string.load_full);
							}
						}
					}

progress.setVisibility(ProgressBar.GONE);