ListView下拉刷新和上拉加载原理

ListView的下拉刷新逻辑：
一、获取ListView的头布局的高度并通过给头布局setPading方法，将头布局隐藏
二、重写ListView的onTouchEvent方法计算出滑动的偏移量dy
三、通过比较偏移量和头布局的高度，进行UI的修改
ListView上拉加载逻辑：
一、获取ListView的脚布局的高度并通过setPading方法，将头布局隐藏
二、调用ListView的setOnScrollListener方法，重写两个方法
1、onScrollStateChanged
当滑动状态是静止状态，并且最后一个条目是脚布局
的时候，显示脚布局，然后加载下一页数据，并修改UI

2、onScroll

接下来直接看代码：

public class RefreshListVeiw extends ListView implements AbsListView.OnScrollListener {public static final int STATE_PULL_TO_REFRESH    = 0;//下拉刷新
    public static final int STATE_RELEASE_TO_REFRESH = 1;//松开刷新
    public static final int STATE_REFRESHING         = 2;//正在刷新
    //当前默认状态为下拉刷新
    private             int mCurrentState            = STATE_PULL_TO_REFRESH;private int             mMeasuredHeight;private float           startY;private View            headerView;private ImageView       ivArrow;private TextView        tvStatus;private ProgressBar     pbLoading;private RotateAnimation upAnimation;private RotateAnimation downAnimation;private View            footView;private int             footViewHight;public RefreshListVeiw(Context context) {this(context, null);}public RefreshListVeiw(Context context, AttributeSet attrs) {this(context, attrs, -1);}public RefreshListVeiw(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);initHeaderView(context);initFootView(context);initAnimation();}private void initHeaderView(Context context) {headerView = View.inflate(context, R.layout.view_header, null);ivArrow = (ImageView) headerView.findViewById(R.id.ivArrow);tvStatus = (TextView) headerView.findViewById(R.id.tvStatus);pbLoading = (ProgressBar) headerView.findViewById(R.id.pbLoading);this.addHeaderView(headerView);//padding值能改变控件的大小
        //获取头布局的高度
        /**
         * View的生命周期和Activity的生命周期
         * 并不是同步的，如果Activity的生命周期中
         * View还没有测量完毕
         */
        headerView.measure(0, 0);mMeasuredHeight = headerView.getMeasuredHeight();headerView.setPadding(0, -mMeasuredHeight, 0, 0);}/**
     * 想要在listView向下滑动的时候，将头布局
     * 一点一点显示出来，这个时候就要响应ListView
     * 的滑动事件
     */
    @Override
    public boolean onTouchEvent(MotionEvent ev) {int action = ev.getAction();switch (action) {case MotionEvent.ACTION_DOWN:startY = ev.getY();break;case MotionEvent.ACTION_MOVE:float moveY = ev.getY();float dy = moveY - startY;/**
                 * 此时ListView第一个可见条目就是
                 * 头布局，头布局此时虽然不可见，
                 * 但是相当于一条线，依然是ListView
                 * 的第一个可见条目
                 */
                int firstVisiblePosition = getFirstVisiblePosition();//如果第一个可见条目是头布局，并且，是向下滑动的时候
                if (firstVisiblePosition == 0 && dy > 0) {//如果当前状态为正在刷新，则不需要再改变布局的高度了
                    if (mCurrentState == STATE_REFRESHING) {break;}//慢慢显示出来
                    int paddingTop = (int) (dy - mMeasuredHeight);headerView.setPadding(0, paddingTop, 0, 0);if (paddingTop < 0) { //下拉刷新状态
                        mCurrentState = STATE_PULL_TO_REFRESH;refreshState();} else { //松开刷新
                        mCurrentState = STATE_RELEASE_TO_REFRESH;refreshState();}return true;//代表消费了事件
                }break;case MotionEvent.ACTION_UP:if (mCurrentState == STATE_PULL_TO_REFRESH) {//隐藏头布局
                    headerView.setPadding(0, -mMeasuredHeight, 0, 0);} else if (mCurrentState == STATE_RELEASE_TO_REFRESH) {//更新状态
                    mCurrentState = STATE_REFRESHING;refreshState();//让头部局完全显示
                    headerView.setPadding(0, 0, 0, 0);//加载数据
                    notifyOnRefresh();}break;}return super.onTouchEvent(ev);}private void refreshState() {switch (mCurrentState) {case STATE_PULL_TO_REFRESH://设置为GONE会影响布局显示的情况
                pbLoading.setVisibility(INVISIBLE);ivArrow.setVisibility(VISIBLE);tvStatus.setText("下拉刷新");ivArrow.setAnimation(upAnimation);break;case STATE_RELEASE_TO_REFRESH:pbLoading.setVisibility(INVISIBLE);ivArrow.setVisibility(VISIBLE);ivArrow.setAnimation(downAnimation);tvStatus.setText("松开刷新");break;case STATE_REFRESHING:pbLoading.setVisibility(VISIBLE);ivArrow.setVisibility(INVISIBLE);//需要把ivArrow的动画移除，才能把ivArrow隐藏起来
                ivArrow.clearAnimation();tvStatus.setText("正在刷新");break;}}private void initAnimation() {upAnimation = new RotateAnimation(0, -180,Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF,0.5f);upAnimation.setDuration(200);upAnimation.setFillAfter(true);downAnimation = new RotateAnimation(-180, 0,Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF,0.5f);downAnimation.setDuration(200);downAnimation.setFillAfter(true);}private boolean isLoadingMore = false;//当滚动状态发生改变的时候，发生的回调
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {if (scrollState == SCROLL_STATE_IDLE && !isLoadingMore) {int lastVisiblePosition = getLastVisiblePosition();if (lastVisiblePosition == getCount() - 1) {// getCount()-1是那一条脚布局的线
                //显示脚布局
                footView.setPadding(0, 0, 0, 0);//需要让脚布局自己显示出来
                setSelection(getCount() - 1);isLoadingMore = true;//加载下一页数据
                notifyOnLoadMore();}}}//这个滚动过程都会进行的回调
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {}//定义回调接口
    public interface onRefreshListener {void onRefresh();void onLoadMore();}//保存接口引用
    private onRefreshListener mListener;public void setOnRefreshListener(onRefreshListener listener) {this.mListener = listener;}private void notifyOnRefresh() {if (mListener != null) {mListener.onRefresh();}}private void notifyOnLoadMore() {if (mListener != null) {mListener.onLoadMore();}}//数据刷新后需要隐藏headerView,并改变状态
    public void onRefreshComplete() {headerView.setPadding(0, -mMeasuredHeight, 0, 0);mCurrentState = STATE_PULL_TO_REFRESH;pbLoading.setVisibility(INVISIBLE);ivArrow.setVisibility(VISIBLE);tvStatus.setText("下拉刷新");}private void initFootView(Context context) {footView = View.inflate(context, R.layout.view_footer, null);footView.measure(0, 0);footViewHight = footView.getMeasuredHeight();footView.setPadding(0, -footViewHight, 0, 0);this.addFooterView(footView);this.setOnScrollListener(this);}public void onLoadMoreComplete() {isLoadingMore = false;footView.setPadding(0, -footViewHight, 0, 0);}}

public class MainActivity extends AppCompatActivity {private RefreshListVeiw mListView;private ArrayList<NewsData> mList = new ArrayList<>();private MainActivity mContent;private MyAdapter    myAdapter;@Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mContent = MainActivity.this;initData();mListView = (RefreshListVeiw) findViewById(R.id.listView);myAdapter = new MyAdapter();mListView.setAdapter(myAdapter);mListView.setOnRefreshListener(new RefreshListVeiw.onRefreshListener() {@Override
            public void onRefresh() {initData();myAdapter.notifyDataSetChanged();//加载数据成功后，隐藏布局
                mListView.onRefreshComplete();}@Override
            public void onLoadMore() {initData();myAdapter.notifyDataSetChanged();mListView.onLoadMoreComplete();}});}private int index = 1;private void initData() {for (int i = 0; i < 10; i++) {NewsData newsData = new NewsData();newsData.content = "我是第" + index + "个item";index++;mList.add(newsData);}}class MyAdapter extends BaseAdapter {@Override
        public int getCount() {return mList.size();}@Override
        public Object getItem(int position) {return mList.get(position);}@Override
        public long getItemId(int position) {return position;}@Override
        public View getView(int position, View convertView, ViewGroup parent) {ViewHolder holder;if (convertView == null) {convertView = View.inflate(mContent, R.layout.view_item_listview, null);holder = new ViewHolder();holder.tvContent = (TextView) convertView.findViewById(R.id.tvContent);convertView.setTag(holder);}holder = (ViewHolder) convertView.getTag();holder.tvContent.setText(mList.get(position).content);return convertView;}}static class ViewHolder {TextView tvContent;}
}

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