ListView Scroll: 动态加载列表内容

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目标：当一个ListView在上下滑动时（scroll up / scroll down），当List中的内容比较多时，会分批load进其中的内容。这在各类型App中很常见。我们现在就是做一个动态加载列表内容功能。

特点：与平时的到了页底再load data不同，假如每次翻页为20条数据，我做的是当ListView滚动停下来时，离页底还有15条数据时就准备load data。也就是说在正常翻页速度下，用户是看不到load data的状态的（为了调试，要设置长一点sleep time以便观察）。

以下是部分关键代码，e.g.

listView.setOnScrollListener(new OnScrollListener() {@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {switch (scrollState) {case OnScrollListener.SCROLL_STATE_IDLE:int firstVisiblePosition = view.getFirstVisiblePosition();            if (sideData.size() < getDataCount()) { // current accumulated items count < total items count            canLoad = true;            } else {            canLoad = false;            }                        if (firstVisiblePosition >= currentPage.get() * pageSize - 15) {// 离页底还有15条数据时就准备load data            int maxPage = getDataCount() / pageSize;            if (currentPage.get() + 1 <= maxPage && canLoad) {                        /* 每次翻页前添加页脚 */                        listView.addFooterView(footer);                        listView.setAdapter(adapter);                        /* 创建子线程，执行翻页 */                        new Thread(new Runnable() {                            public void run() {                                try {                                    Thread.sleep(3000);                                } catch (InterruptedException e) {                                    e.printStackTrace();                                }                                List<String> sideDataByPage = getData(currentPage.get() + 1);                                mHandler.sendMessage(mHandler.obtainMessage(1, sideDataByPage));//add new items                            }                        }).start();                    } else if (canLoad) {                    List<String> sideDataByPage = getData(currentPage.get() + 1);                    mHandler.sendMessage(mHandler.obtainMessage(2, sideDataByPage));//add last items                    }            }break;case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:break;case OnScrollListener.SCROLL_STATE_FLING:break;default:break;}}

private Handler mHandler = new Handler() {@SuppressWarnings("unchecked")public void handleMessage(Message msg) {switch (msg.what) {case 1:/* 页脚显示完就删掉 */if (listView.getFooterViewsCount() > 0)listView.removeFooterView(footer);sideData.addAll((List<String>) msg.obj);adapter.notifyDataSetChanged();currentPage.getAndIncrement();break;case 2:sideData.addAll((List<String>) msg.obj);adapter.notifyDataSetChanged();currentPage.getAndIncrement();break;default:break;}}};

XML

- side.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:background="@android:color/background_dark"    android:orientation="vertical" >    <ListView        android:id="@+id/side_list"        android:layout_width="match_parent"        android:layout_height="0dp"        android:layout_weight="2"        >    </ListView>        </LinearLayout>

- side_items.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:background="@android:color/background_dark"    android:orientation="vertical" >    <TextView        android:id="@+id/side_text_view"        android:layout_width="match_parent"        android:layout_height="0dp"        android:textSize="18sp"        android:textColor="@android:color/white"        android:lineSpacingExtra="3dp"        android:lineSpacingMultiplier="1.5"        android:layout_weight="2"        >    </TextView>        </LinearLayout>

- side_footer.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:background="@android:color/background_dark"    android:orientation="horizontal" >    <ProgressBar        style="?android:attr/process"        android:layout_width="18dp"        android:layout_height="wrap_content" />     <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="正在加载....."        android:textSize="18sp"        android:textColor="@android:color/white"        android:lineSpacingExtra="3dp"        android:lineSpacingMultiplier="1.5"         /> </LinearLayout>

一些以便调试用到的辅助代码，e.g.

public List<String> getData(int currentPage) {List<String> sideDataByPage = new ArrayList<String>();int maxPosition = currentPage * pageSize;if (maxPosition > getDataCount()) {maxPosition = getDataCount();}for (int position = (currentPage - 1) * pageSize; position < maxPosition; position++) {sideDataByPage.add(mStrings[position].substring(0, (mStrings[position].length() < 12)?mStrings[position].length():12));  // 防止字符过长换行}return sideDataByPage;}

private String[] mStrings = {"test", "test1", ...}

public int getDataCount() {// total items countreturn mStrings.length;}

public class Side {private View sideView;private ListView listView;private View footer;final private int pageSize = 20;private List<String> sideData = new ArrayList<String>();private BaseAdapter adapter;private boolean canLoad = true;private AtomicInteger currentPage = new AtomicInteger(1);private SlidingViewGroup slidingViewGroup;public Side(final Activity activity, final Context context, final SlidingViewGroup slidingViewGroup) {setSlidingViewGroup(slidingViewGroup);sideView = LayoutInflater.from(context).inflate(R.layout.side, null);footer = LayoutInflater.from(context).inflate(R.layout.side_footer, null);sideData.addAll(getData(1));adapter = new ArrayAdapter<String>(context, R.layout.side_items,R.id.side_text_view, sideData);listView = (ListView) this.sideView.findViewById(R.id.side_list);listView.setAdapter(adapter);...

效果图

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