Android開源中國客戶端學習 上拉刷新 底部加載 的listview <4>

此次學習一些osc客戶端的 上拉刷新 底部加載 的listview 這裏仍是以加載新聞爲例

 osc上的下拉刷新 和底部自動加載下一頁是和qq空間等app類似的，那就學習一下

其實osc是使用了一個開源的控件 --PullToRefreshListView

具體代碼恕不粘貼

具體的使用在fragme_news.xml中

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

在這裏說一點，其實osc各個功能的切換隻不過是 切換四個fragmelayout的可見性。具體請查看main.xml

先說下拉刷新,其實使用了PullToRefreshListView這個控件後,使用下拉就很簡單了 只需監聽一個下來事件就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後就可觸發這個事件了,而後就loadLvNewsData方法載入數據了,咱們再看一下最後一個參數,在調用loadLvNewsData這裏就會 isRefresh = true; 

ok 既然isRefresh= true 了 那麼無論是否有緩存可讀都會從網絡讀取數據到listview

在news的handler中可能還須要出來上次刷新時間 在獲取handler的構造函數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) {//是否顯示上次何時刷新
					lv.onRefreshComplete();
					lv.setSelection(0);
				}

而後是滑動到底部 顯示progressbar並加載下一頁數據

其實就是控制listview的footview的顯示狀態:當listview滑動到最底部時,把footview由"更多"改爲progressbar 並顯示"加載中..."

lvNews.addFooterView(lvNews_footer);// 添加底部視圖 必須在setAdapter前 添加FootView

看看底部加載的核心代碼:

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

				// 數據爲空--不用繼續下面代碼了
				if (lvNewsData.isEmpty())
					return;

				// 判斷是否滾動到底部
				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);
					// 當前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);
				}
			}

那麼就分析一下

首先判斷是否滑動到底部

// 判斷是否滾動到底部
				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 塊 作判斷是否到底部不是什麼好方法,會不會很耗費資源?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);
					// 當前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);
				}

注意這裏有一個

int lvDataState = StringUtils.toInt(lvNews.getTag());和判斷lvDataState == UIHelper.LISTVIEW_DATA_MORE這是爲了防止重複加載load 數據的.

OK 如今就開始使用loadLvNewsData函數load數據了,那何時把progressbar消失呢?固然是在載入完了了數據以後,那麼根據第一篇文章咱們知道確定是在handler中處理了

其實實在初始化的時候

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

這裏lvNews_foot_more, lvNews_foot_progress,兩個參數就分別是footerview的兩個控件了

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);

						// 特殊處理-熱門動彈不能翻頁
						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);