我如何创建一个列表,当你到达列表的末尾时,我会收到通知,这样我就可以加载更多的项目?
当前回答
只是想为我的应用程序贡献一个解决方案。
它也基于OnScrollListener接口,但我发现它在低端设备上的滚动性能要好得多,因为在滚动操作期间不执行任何可见/总计数计算。
Let your ListFragment or ListActivity implement OnScrollListener Add the following methods to that class: @Override public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { //leave this empty } @Override public void onScrollStateChanged(AbsListView listView, int scrollState) { if (scrollState == SCROLL_STATE_IDLE) { if (listView.getLastVisiblePosition() >= listView.getCount() - 1 - threshold) { currentPage++; //load more list items: loadElements(currentPage); } } } where currentPage is the page of your datasource that should be added to your list, and threshold is the number of list items (counted from the end) that should, if visible, trigger the loading process. If you set threshold to 0, for instance, the user has to scroll to the very end of the list in order to load more items. (optional) As you can see, the "load-more check" is only called when the user stops scrolling. To improve usability, you may inflate and add a loading indicator to the end of the list via listView.addFooterView(yourFooterView). One example for such a footer view: <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/footer_layout" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="10dp" > <ProgressBar android:id="@+id/progressBar1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerVertical="true" android:layout_gravity="center_vertical" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerVertical="true" android:layout_toRightOf="@+id/progressBar1" android:padding="5dp" android:text="@string/loading_text" /> </RelativeLayout> (optional) Finally, remove that loading indicator by calling listView.removeFooterView(yourFooterView) if there are no more items or pages.
其他回答
你可以在onScrollListener的帮助下检测列表的结尾,工作代码如下:
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (view.getAdapter() != null && ((firstVisibleItem + visibleItemCount) >= totalItemCount) && totalItemCount != mPrevTotalItemCount) {
Log.v(TAG, "onListEnd, extending list");
mPrevTotalItemCount = totalItemCount;
mAdapter.addMoreData();
}
}
另一种方法(内部适配器)如下所示:
public View getView(int pos, View v, ViewGroup p) {
if(pos==getCount()-1){
addMoreData(); //should be asynctask or thread
}
return view;
}
注意,这个方法将被多次调用,因此需要添加另一个条件来阻止多次调用addMoreData()。
当你将所有元素添加到列表中时,请在适配器中调用notifyDataSetChanged()来更新视图(它应该在UI线程runOnUiThread上运行)
只是想为我的应用程序贡献一个解决方案。
它也基于OnScrollListener接口,但我发现它在低端设备上的滚动性能要好得多,因为在滚动操作期间不执行任何可见/总计数计算。
Let your ListFragment or ListActivity implement OnScrollListener Add the following methods to that class: @Override public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { //leave this empty } @Override public void onScrollStateChanged(AbsListView listView, int scrollState) { if (scrollState == SCROLL_STATE_IDLE) { if (listView.getLastVisiblePosition() >= listView.getCount() - 1 - threshold) { currentPage++; //load more list items: loadElements(currentPage); } } } where currentPage is the page of your datasource that should be added to your list, and threshold is the number of list items (counted from the end) that should, if visible, trigger the loading process. If you set threshold to 0, for instance, the user has to scroll to the very end of the list in order to load more items. (optional) As you can see, the "load-more check" is only called when the user stops scrolling. To improve usability, you may inflate and add a loading indicator to the end of the list via listView.addFooterView(yourFooterView). One example for such a footer view: <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/footer_layout" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="10dp" > <ProgressBar android:id="@+id/progressBar1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerVertical="true" android:layout_gravity="center_vertical" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerVertical="true" android:layout_toRightOf="@+id/progressBar1" android:padding="5dp" android:text="@string/loading_text" /> </RelativeLayout> (optional) Finally, remove that loading indicator by calling listView.removeFooterView(yourFooterView) if there are no more items or pages.
到目前为止,我见过的最好的解决方案是在FastAdapter库中用于回收器视图。它有一个EndlessRecyclerOnScrollListener。
下面是一个示例用法:EndlessScrollListActivity
一旦我使用它无休止的滚动列表,我已经意识到设置是一个非常强大的。我强烈推荐。
下面是一个解决方案,它也可以很容易地在ListView加载时显示加载视图。
你可以在这里看到这些类:
https://github.com/CyberEagle/OpenProjects/blob/master/android-projects/widgets/src/main/java/br/com/cybereagle/androidwidgets/helper/ListViewWithLoadingIndicatorHelper.java - Helper,使它可以使用功能而不扩展从SimpleListViewWithLoadingIndicator。
https://github.com/CyberEagle/OpenProjects/blob/master/android-projects/widgets/src/main/java/br/com/cybereagle/androidwidgets/listener/EndlessScrollListener.java -当用户即将到达ListView的底部时,监听器开始加载数据。
https://github.com/CyberEagle/OpenProjects/blob/master/android-projects/widgets/src/main/java/br/com/cybereagle/androidwidgets/view/SimpleListViewWithLoadingIndicator.java - EndlessListView。您可以直接使用这个类,也可以从它扩展。
一种解决方案是实现OnScrollListener,并在ListAdapter的onScroll方法中以方便的状态对其进行更改(如添加项目等)。
下面的ListActivity显示了一个整数列表,从40开始,当用户滚动到列表末尾时添加项。
public class Test extends ListActivity implements OnScrollListener {
Aleph0 adapter = new Aleph0();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setListAdapter(adapter);
getListView().setOnScrollListener(this);
}
public void onScroll(AbsListView view,
int firstVisible, int visibleCount, int totalCount) {
boolean loadMore = /* maybe add a padding */
firstVisible + visibleCount >= totalCount;
if(loadMore) {
adapter.count += visibleCount; // or any other amount
adapter.notifyDataSetChanged();
}
}
public void onScrollStateChanged(AbsListView v, int s) { }
class Aleph0 extends BaseAdapter {
int count = 40; /* starting amount */
public int getCount() { return count; }
public Object getItem(int pos) { return pos; }
public long getItemId(int pos) { return pos; }
public View getView(int pos, View v, ViewGroup p) {
TextView view = new TextView(Test.this);
view.setText("entry " + pos);
return view;
}
}
}
显然,对于长时间运行的操作(如加载web-data),您应该使用单独的线程,并可能希望在最后一个列表项中指示进度(如市场或gmail应用程序)。
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