android 学习 ListView使用补充

　　前面两篇学习适配器的时候用的就是listview，主要是简单的添加，今晚在看了下listview滚动状态事件和动态加载数据，一个小demo。

listview的滚动状态主要有三种，onScrollStateChanged

SCROLL_STATE_IDLE   空闲状态 ，既是滚动停止状态

SCROLL_STATE_FLING  滚动状态 ， 既是滚动中的状态

SCROLL_STATE_TOUCH_SCROLL  触摸后滚动 ， 刚开始滚动的状态

/**
 * Callback method to be invoked while the list view or grid view is being scrolled. If the
 * view is being scrolled, this method will be called before the next frame of the scroll is
 * rendered. In particular, it will be called before any calls to
 * {@link Adapter#getView(int, View, ViewGroup)}.
 *
 * @param view The view whose scroll state is being reported
 *
 * @param scrollState The current scroll state. One of {@link #SCROLL_STATE_IDLE},
 * {@link #SCROLL_STATE_TOUCH_SCROLL} or {@link #SCROLL_STATE_IDLE}.
 */

onScroll 函数应该是滚动完成后的回调函数

firstVisibleItem  该页面第一个可视索引

visibleItemCount  该页面显示的列表个数

totalItemCount    整个listview 的item 个数

源码注释

* Callback method to be invoked when the list or grid has been scrolled. This will be
* called after the scroll has completed

* @param view The view whose scroll state is being reported
* @param firstVisibleItem the index of the first visible cell (ignore if
*        visibleItemCount == 0)
* @param visibleItemCount the number of visible cells
* @param totalItemCount the number of items in the list adaptor

 adapter.notifyDataSetChanged()　　是适配器数据改变之后需要通过该函数，通知listview

知道这两个回调，就可以做到动态加载数据了，既是在滚动完成后，判断是否到达末尾，如果到达末尾就添加进一个数据，然后通知listview更新。

public class ArrayAdapterActivity extends Activity {

    private ListView listView;
    private ArrayAdapter<String> adapter;
    private ArrayList<String>  list;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_array_adapter);
        listView = (ListView)findViewById(R.id.listView3);
        list = new ArrayList<String>();
        adapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,getData());
        listView.setAdapter(adapter);
        listView.setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {
                switch(scrollState){
                    case AbsListView.OnScrollListener.SCROLL_STATE_IDLE:{
                        Log.i("scroll","空闲状态");
                        break;
                    }
                    case AbsListView.OnScrollListener.SCROLL_STATE_FLING:{
                        Log.i("scroll","滚动状态");
                        break;
                    }
                    case AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:{
                        Log.i("scroll","触摸后滚动");
                        break;
                    }
                }
            }
            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                if(firstVisibleItem + visibleItemCount == totalItemCount){
                    Log.i("scroll","到达底部");
                    list.add(""+list.size());
                    adapter.notifyDataSetChanged();
                }
            }
        });
    }
    ArrayList<String> getData(){
        for(int i =0;i<40;i++) {
            list.add("" + i);
        }
        return list;
    }
}