ListView加载更多

主要是对OnScrllListener的使用介绍,有两个方法来监听滑动的状态，onScroll()和onScrollStateChanged()。

new AbsListView.OnScrollListener() {
            /**
             *正在滚动时回调，回调2-3次，手指没抛则回调2次。scrollState = 2的这次不回调
             *回调顺序如下
             *第1次：scrollState = SCROLL_STATE_TOUCH_SCROLL(1) 正在滚动
             *第2次：scrollState = SCROLL_STATE_FLING(2) 手指做了抛的动作（手指离开屏幕前，用力滑了一下）
             *第3次：scrollState = SCROLL_STATE_IDLE(0) 停止滚动
             */
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {
                //当停止滚动时
                if (scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE) {
                    //do something
                }
            }

            /**
             * 滚动时一直回调，直到停止滚动时才停止回调。单击时回调一次。
             *firstVisibleItem：当前能看见的第一个列表项ID（从0开始）
             *visibleItemCount：当前能看见的列表项个数（小半个也算）
             *totalItemCount：列表项共数
             */
            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                //否滚到最后一行
                if (firstVisibleItem + visibleItemCount == totalItemCount && totalItemCount > 0) {
                    //do something
                }
            }
        };

下面用Listview的加载更多实例来说明。

重写的Listview，实现了滑动监听。

public class LoaderListView extends ListView implements AbsListView.OnScrollListener {
    private Context mContext;
    private boolean isCanScroll = false;
    private List list = new ArrayList();
    /**
     * 最后可见条目的索引
     */
    private int lastVisibleIndex = 0;
    private View footView;
    private MainActivity.CurAdapter adapter;

    private Handler loaderHander = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            loaderMore();
        }
    };

    public LoaderListView(Context context) {
        super(context);
        this.mContext = context;
        init();
    }

    public LoaderListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.mContext = context;
        init();
    }

    public LoaderListView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.mContext = context;
        init();
    }

    private void init() {
        footView = LayoutInflater.from(mContext).inflate(R.layout.item_foot, null);
        addFooterView(footView);
        setOnScrollListener(this);
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        if (isCanScroll && OnScrollListener.SCROLL_STATE_IDLE == scrollState && lastVisibleIndex < list.size()) {
            loaderHander.sendEmptyMessageDelayed(0, 2000);
        }
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        lastVisibleIndex = firstVisibleItem + visibleItemCount - 1;
        if (firstVisibleItem + 15 < totalItemCount) {
            isCanScroll = false;
        } else {
            if (lastVisibleIndex == list.size()) {
                removeFooterView(footView);
            } else {
                isCanScroll = true;
            }
        }
    }

    /**
     * 加载更多
     */
    private void loaderMore() {
        if (lastVisibleIndex + 10 < list.size()) {
            lastVisibleIndex += 10;
        } else {
            lastVisibleIndex = list.size();
        }
        adapter.setCountLength(lastVisibleIndex);
    }

    public List getList() {
        return list;
    }

    public void setList(List list) {
        this.list = list;
    }

    public MainActivity.CurAdapter getCurAdapter() {
        return adapter;
    }

    public void setCurAdapter(MainActivity.CurAdapter adapter) {
        this.adapter = adapter;
    }
}

活动中，主要是传入集合和适配器。

public class MainActivity extends Activity {
    private MainActivity mContext;
    private int lastPress = 0;
    private boolean delState = false;
    private List<String> curList = new ArrayList<>();

    private LoaderListView curListView;
    private CurAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }

    private void init() {
        mContext = this;

        for (int i = 0; i < 100; i++) {
            curList.add("第" + i + ":行数据");
        }

        curListView = (LoaderListView) findViewById(R.id.lv_contents);
        adapter = new CurAdapter();
        curListView.setAdapter(adapter);

        curListView.setList(curList);
        curListView.setCurAdapter(adapter);
    }


    public class CurAdapter extends BaseAdapter {
        private int count = 0;

        public CurAdapter() {
            if (0 == count) {
                if (15 > curList.size()) {
                    count = curList.size();
                } else {
                    count = 15;
                }
            }
        }

        public void setCountLength(int count) {
            this.count = count;
            notifyDataSetChanged();
        }

        @Override
        public int getCount() {
            return count;
        }

        @Override
        public Object getItem(int position) {
            return position;
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (null == convertView) {
                convertView = LayoutInflater.from(mContext).inflate(R.layout.item_content, null);
            }

            ((TextView) convertView.findViewById(R.id.tv_content)).setText(curList.get(position));
            return convertView;
        }
    }
}

活动布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <cn.com.myapplication.LoaderListView
        android:id="@+id/lv_contents"
        android:layout_width="match_parent"
        android:layout_height="match_parent"></cn.com.myapplication.LoaderListView>
</RelativeLayout>

子项布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:background="#FFFFFF"
    android:layout_height="40dp">

    <RelativeLayout
        android:id="@+id/rela_content"
        android:layout_width="match_parent"
        android:visibility="visible"
        android:layout_height="40dp">

        <TextView
            android:id="@+id/tv_content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="content"
            android:textColor="#001122"
            android:gravity="center" />
    </RelativeLayout>
</RelativeLayout>

在适配器中，对子项数量的处理,是针对那种提前就把数据都取完了的情况：

public CurAdapter() {
            if (0 == count) {
                if (15 > curList.size()) {
                    count = curList.size();
                } else {
                    count = 15;
                }
            }
        }

        public void setCountLength(int count) {
            this.count = count;
            notifyDataSetChanged();
        }

如果加载更多的数据需要去网络上请求的话，那么最好是在loaderMore()中，开启去请求，然后发送handler刷新数据。

   /**
     * 加载更多
     */
    private void loaderMore() {
        if (lastVisibleIndex + 10 < list.size()) {
            lastVisibleIndex += 10;
        } else {
            lastVisibleIndex = list.size();
        }
        adapter.setCountLength(lastVisibleIndex);
    }