使用Android实现一个简单的下拉刷新控件

/**
 * @author luowang8
 * @date 2020-08-21 10:54
 * @desc 下拉刷新控件
 */
public class PullRefreshView extends LinearLayout {
 
 
 /**
 * 头部tag
 */
 public static final String HEADER_TAG = "HEADER_TAG";
 
 /**
 * 列表tag
 */
 public static final String LIST_TAG = "LIST_TAG";
 
 /**
 * tag
 */
 private static final String TAG = "PullRefreshView";
 
 /**
 * 默认初始状态
 */
 private @State
 int mState = State.INIT;
 
 /**
 * 是否被拖拽
 */
 private boolean mIsDragging = false;
 
 /**
 * 上下文
 */
 private Context mContext;
 
 
 /**
 * RecyclerView
 */
 private RecyclerView mRecyclerView;
 
 /**
 * 顶部刷新头
 */
 private View mHeaderView;
 
 /**
 * 初始Y的坐标
 */
 private int mInitMotionY;
 
 /**
 * 上一次Y的坐标
 */
 private int mLastMotionY;
 
 /**
 * 手指触发滑动的临界距离
 */
 private int mSlopTouch;
 
 /**
 * 触发刷新的临界值
 */
 private int mRefreshHeight = 200;
 
 /**
 * 滑动时长
 */
 private int mDuring = 300;
 
 /**
 * 用户刷新监听器
 */
 private OnRefreshListener mOnRefreshListener;
 
 /**
 * 刷新文字提示
 */
 private TextView mRefreshTip;
 
 /**
 * 是否可拖拽, 因为在刷新头自由滑动和刷新状态的时候，
 * 我们应该保持界面不被破坏
 */
 private boolean mIsCanDrag = true;
 
 /**
 * 头部布局
 */
 private LayoutParams mHeaderLayoutParams;
 
 /**
 * 列表布局
 */
 private LayoutParams mListLayoutParams;
 
 /**
 * 属性动画
 */
 private ValueAnimator mValueAnimator;
 
 
 
 /// 分割 ///
 
 
 /**
 * @param context
 */
 public PullRefreshView(Context context) {
 this(context, null);
 }
 
 /**
 * @param context
 * @param attrs
 */
 public PullRefreshView(Context context, @Nullable AttributeSet attrs) {
 this(context, attrs, 0);
 }
 
 /**
 * @param context
 * @param attrs
 * @param defStyleAttr
 */
 public PullRefreshView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
 super(context, attrs, defStyleAttr);
 
 mContext = context;
 
 initView();
 }
 
 public RecyclerView getRecyclerView() {
 return mRecyclerView;
 }
 
 /**
 * 设置RecyclerView
 *
 * @param recyclerView
 */
 public void addRecyclerView(RecyclerView recyclerView) {
 
 if (recyclerView == null) {
 return;
 }
 
 View view = findViewWithTag(LIST_TAG);
 if (view != null) {
 removeView(view);
 }
 
 this.mRecyclerView = recyclerView;
 this.mRecyclerView.setTag(LIST_TAG);
 addView(recyclerView, mListLayoutParams);
 }
 
 /**
 * 设置自定义刷新头部
 * @param headerView
 */
 public void addHeaderView(View headerView) {
 
 if (headerView == null) {
 return;
 }
 
 View view = findViewWithTag(HEADER_TAG);
 if (view != null) {
 removeView(view);
 }
 
 this.mHeaderView = headerView;
 this.mHeaderView.setTag(HEADER_TAG);
 addView(mHeaderView, mHeaderLayoutParams);
 }
 
 /**
 * @param onRefreshListener
 */
 public void setOnRefreshListener(OnRefreshListener onRefreshListener) {
 mOnRefreshListener = onRefreshListener;
 }
 
 /**
 * 初始化View
 */
 private void initView() {
 
 setOrientation(LinearLayout.VERTICAL);
 
 Context context = getContext();
 /** 1、添加刷新头Header */
 mHeaderView = LayoutInflater.from(context).inflate(R.layout.layout_refresh_header, null);
 mHeaderView.setTag(HEADER_TAG);
 mRefreshTip = mHeaderView.findViewById(R.id.content);
 mHeaderLayoutParams = new LayoutParams(LayoutParams.MATCH_PARENT,
 DensityUtil.dip2px(mContext, 500)
 );
 this.addView(mHeaderView, mHeaderLayoutParams);
 
 /** 2、添加内容RecyclerView */
 mRecyclerView = new RecyclerView(context);
 mRecyclerView.setTag(LIST_TAG);
 mListLayoutParams = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
 this.addView(mRecyclerView, mListLayoutParams);
 
 /** 3、一开始的时候要让Header看不见，设置向上的负paddingTop */
 setPadding(0, -DensityUtil.dip2px(mContext, 500), 0, 0);
 
 ViewConfiguration viewConfiguration = ViewConfiguration.get(context);
 mSlopTouch = viewConfiguration.getScaledTouchSlop();
 
 setState(State.INIT);
 
 }
 
 /**
 * 设置状态，每个状态下，做不同的事情
 *
 * @param state 状态
 */
 private void setState(@State int state) {
 
 switch (state) {
 case State.INIT:
 initState();
 break;
 
 case State.DRAGGING:
 dragState();
 break;
 
 case State.READY:
 readyState();
 break;
 
 case State.REFRESHING:
 refreshState();
 break;
 
 case State.FLING:
 flingState();
 break;
 
 default:
 break;
 }
 
 mState = state;
 }
 
 /**
 * 处理初始化状态方法
 */
 private void initState() {
 
 // 只有在初始状态时，恢复成可拖拽
 mIsCanDrag = true;
 mIsDragging = false;
 mRefreshTip.setText("下拉刷新");
 }
 
 /**
 * 处理拖拽时方法
 */
 private void dragState() {
 mIsDragging = true;
 }
 
 /**
 * 拖拽距离超过header高度时，如何处理
 */
 private void readyState() {
 mRefreshTip.setText("松手刷新");
 }
 
 /**
 * 用户刷新时，如何处理
 */
 private void refreshState() {
 if (mOnRefreshListener != null) {
 mOnRefreshListener.onRefresh();
 }
 
 mIsCanDrag = false;
 mRefreshTip.setText("正在刷新,请稍后...");
 }
 
 /**
 * 自由滚动时，如何处理
 */
 private void flingState() {
 mIsDragging = false;
 mIsCanDrag = false;
 
 /** 自由滚动状态可以从两个状态进入：
 * 1、READY状态。
 * 2、其他状态。
 *
 * ！滑动均需要平滑滑动
 * */
 if (mState == State.READY) {
 
 Log.e(TAG, "flingState: 从Ready状态开始自由滑动");
 // 从准备状态进入，刷新头滑到 200 的位置
 
 smoothScroll(getScrollY(), -mRefreshHeight);
 }
 else {
 
 Log.e(TAG, "flingState: 松手后，从其他状态开始自由滑动");
 // 从刷新状态进入，刷新头直接回到最初默认的位置
 // 即: 滑出界面，ScrollY 变成 0
 smoothScroll(getScrollY(), 0);
 }
 
 }
 
 /**
 * 光滑滚动
 * @param startPos 开始位置
 * @param targetPos 结束位置
 */
 private void smoothScroll(int startPos, final int targetPos) {
 
 // 如果有动画正在播放，先停止
 if (mValueAnimator != null && mValueAnimator.isRunning()) {
 mValueAnimator.cancel();
 mValueAnimator.end();
 mValueAnimator = null;
 }
 
 // 然后开启动画
 mValueAnimator = ValueAnimator.ofInt(getScrollY(), targetPos);
 mValueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
 @Override
 public void onAnimationUpdate(ValueAnimator valueAnimator) {
 int value = (int) valueAnimator.getAnimatedValue();
 scrollTo(0, value);
 
 if (getScrollY() == targetPos) {
 if (targetPos != 0) {
 setState(State.REFRESHING);
 }
 else {
 setState(State.INIT);
 }
 }
 }
 });
 
 mValueAnimator.setDuration(mDuring);
 mValueAnimator.start();
 }
 
 /**
 * 是否准备好触发下拉的状态了
 */
 private boolean isReadyToPull() {
 
 if (mRecyclerView == null) {
 return false;
 }
 
 LinearLayoutManager manager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
 
 if (manager == null) {
 return false;
 }
 
 if (mRecyclerView != null && mRecyclerView.getAdapter() != null) {
 View child = mRecyclerView.getChildAt(0);
 int height = child.getHeight();
 if (height > mRecyclerView.getHeight()) {
 return child.getTop() == 0 && manager.findFirstVisibleItemPosition() == 0;
 }
 else {
 return manager.findFirstCompletelyVisibleItemPosition() == 0;
 }
 }
 
 return false;
 }
 
 @Override
 public boolean onInterceptTouchEvent(MotionEvent ev) {
 
 int action = ev.getAction();
 
 Log.e(TAG, "onInterceptTouchEvent: action = " + action);
 
 if (!mIsCanDrag) {
 return true;
 }
 
 if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
 mIsDragging = false;
 return false;
 }
 
 if (mIsDragging && action == MotionEvent.ACTION_MOVE) {
 return true;
 }
 
 switch (action) {
 case MotionEvent.ACTION_MOVE:
 int diff = (int) (ev.getY() - mLastMotionY);
 if (Math.abs(diff) > mSlopTouch && diff > 1 && isReadyToPull()) {
 mLastMotionY = (int) ev.getY();
 mIsDragging = true;
 }
 break;
 
 case MotionEvent.ACTION_DOWN:
 if (isReadyToPull()) {
 setState(State.INIT);
 mInitMotionY = (int) ev.getY();
 mLastMotionY = (int) ev.getY();
 }
 break;
 
 default:
 break;
 }
 
 return mIsDragging;
 }
 
 @Override
 public boolean onTouchEvent(MotionEvent event) {
 
 int action = event.getAction();
 
 Log.e(TAG, "onTouchEvent: action = " + action);
 
 if (!mIsCanDrag) {
 return false;
 }
 
 switch (action) {
 case MotionEvent.ACTION_DOWN:
 if (isReadyToPull()) {
 setState(State.INIT);
 mInitMotionY = (int) event.getY();
 mLastMotionY = (int) event.getY();
 }
 break;
 
 case MotionEvent.ACTION_MOVE:
 
 if (mIsDragging) {
 mLastMotionY = (int) event.getY();
 setState(State.DRAGGING);
 
 pullScroll();
 return true;
 }
 
 break;
 
 case MotionEvent.ACTION_UP:
 case MotionEvent.ACTION_CANCEL:
 mIsDragging = false;
 setState(State.FLING);
 break;
 
 default:
 break;
 
 }
 
 return true;
 }
 
 /**
 * 下拉移动界面，拉出刷新头
 */
 private void pullScroll() {
 /** 滚动值 = 初始值 - 结尾值 */
 int scrollValue = (mInitMotionY - mLastMotionY) / 3;
 
 if (scrollValue > 0) {
 scrollTo(0, 0);
 return;
 }
 
 if (Math.abs(scrollValue) > mRefreshHeight
 && mState == State.DRAGGING) {
 // 约定：如果偏移量超过 200(这个值，表示是否可以启动刷新的临界值，可任意定),
 // 那么状态变成 State.READY
 Log.e(TAG, "pullScroll: 超过了触发刷新的临界值");
 setState(State.READY);
 }
 
 scrollTo(0, scrollValue);
 }
 
 /**
 * 刷新完成，需要调用方主动发起，才能完成将刷新头收起
 */
 public void refreshComplete() {
 mRefreshTip.setText("刷新完成！");
 setState(State.FLING);
 }
 
 @IntDef({
  State.INIT
  , State.DRAGGING
  , State.READY
  , State.REFRESHING
  , State.FLING,
  })
 @Retention(RetentionPolicy.SOURCE)
 public @interface State {
 
 /**
 * 初始状态
 */
 int INIT = 1;
 
 /**
 * 手指拖拽状态
 */
 int DRAGGING = 2;
 
 /**
 * 就绪状态，松开手指后，可以刷新
 */
 int READY = 3;
 
 /**
 * 刷新状态，这个状态下，用户用于发起刷新请求
 */
 int REFRESHING = 4;
 
 /**
 * 松开手指，顶部自然回弹的状态，有两种表现
 * 1、手指释放时的高度大于刷新头的高度。
 * 2、手指释放时的高度小于刷新头的高度。
 */
 int FLING = 5;
 }
 
 /**
 * 用户刷新状态的操作
 */
 public interface OnRefreshListener {
 void onRefresh();
 }
 
}