Android滑动回弹效果

左手的ㄟ右手 2022-08-21 04:45 286阅读 0赞

原理：

addHeaderView里做的事：

1.测量出header的宽高，调用了measureView方法  
2.设置LayoutParams，宽：MATCH\_PARENT，高：10  
3.设置topMargin的值为负的header的高度,即将header隐藏在屏幕最上方  
  
  
onInterceptTouchEvent：

如果滑动距离为零，让onInterceptTouchEvent处理。屏幕没有滑动效果。

onTouchEvent：  
如果滑动距离大于零，让onTouchEvent处理。在滑动过程中不断的计算header的topMargin，让屏幕有滑动效果。

代码：

/** * android回弹效果 by haidaye */ public class HaidayeView extends LinearLayout {
        private int mLastMotionY;
        /** * 头部view */ private View mHeaderView;
        private LayoutInflater mInflater;
        private ScrollView mScrollView;
        /** * 头部view的高 */ private int mHeaderViewHeight;
    
        public HaidayeView(Context context, AttributeSet attrs) {
            super(context, attrs);
            init();
        }
    
        public HaidayeView(Context context) {
            super(context);
            init();
        }
    
        private void init() {
            // Load all of the animations we need in code rather than through XML
            mInflater = LayoutInflater.from(getContext());
            // header view 在此添加,保证是第一个添加到linearlayout的最上端
            addHeaderView();
        }
    
        private void addHeaderView() {
            // header view
            mHeaderView = mInflater.inflate(R.layout.header, this, false);
            measureView(mHeaderView);
            mHeaderViewHeight = mHeaderView.getMeasuredHeight();
            LayoutParams params = new LayoutParams(LayoutParams.MATCH_PARENT,
                    mHeaderViewHeight);
            // 设置topMargin的值为负的header View高度,即将其隐藏在最上方
            params.topMargin = -(mHeaderViewHeight);
            addView(mHeaderView, params);
    
        }
    
        @Override
        protected void onFinishInflate() {
            super.onFinishInflate();
            initContentAdapterView();
        }
    
        private void initContentAdapterView() {
            mScrollView = (ScrollView) getChildAt(1);
        }
    
        private void measureView(View child) {
            ViewGroup.LayoutParams p = child.getLayoutParams();
            if (p == null) {
                p = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT,
                        ViewGroup.LayoutParams.WRAP_CONTENT);
            }
    
            int childWidthSpec = ViewGroup.getChildMeasureSpec(0, 0 + 0, p.width);
            int lpHeight = p.height;
            int childHeightSpec;
            if (lpHeight > 0) {
                childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight,
                        MeasureSpec.EXACTLY);
            } else {
                childHeightSpec = MeasureSpec.makeMeasureSpec(0,
                        MeasureSpec.UNSPECIFIED);
            }
            child.measure(childWidthSpec, childHeightSpec);
        }
    
        @Override
        public boolean onInterceptTouchEvent(MotionEvent e) {
            int y = (int) e.getRawY();
            switch (e.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    // 首先拦截down事件,记录y坐标
                    mLastMotionY = y;
                    break;
                case MotionEvent.ACTION_MOVE:
                    // deltaY > 0 是向下运动,< 0是向上运动
                    int deltaY = y - mLastMotionY;
                    if (isRefreshViewScroll(deltaY)) {
                        return true;
                    }
                    mLastMotionY = y;
                    break;
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_CANCEL:
                    break;
            }
            return false;
        }
    
        /*
         * 如果在onInterceptTouchEvent()方法中没有拦截(即onInterceptTouchEvent()方法中 return
         * false)则由PullToRefreshView 的子View来处理;否则由下面的方法来处理(即由HaidayeView自己来处理)
         */
        @Override
        public boolean onTouchEvent(MotionEvent event) {
            int y = (int) event.getRawY();
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    // onInterceptTouchEvent已经记录
                    // mLastMotionY = y;
                    break;
                case MotionEvent.ACTION_MOVE:
                    int deltaY = y - mLastMotionY;
                    headerPrepareToRefresh(deltaY);
                    mLastMotionY = y;
                    break;
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_CANCEL:
                    int topMargin = getHeaderTopMargin();
                    setHeaderTopMargin(-mHeaderViewHeight);
                    break;
                case MotionEvent.ACTION_POINTER_DOWN://设置多点触控
                    this.mLastMotionY = y;
                    break;
            }
            return super.onTouchEvent(event);
        }
    
        /** * 是否应该到了父View,即PullToRefreshView滑动 * * @param deltaY , deltaY > 0 是向下运动,< 0是向上运动 * @return */ private boolean isRefreshViewScroll(int deltaY) {
            // 对于ScrollView
            if (mScrollView != null) {
                // 子scroll view滑动到最顶端
                View child = mScrollView.getChildAt(0);
                if (deltaY > 0 && mScrollView.getScrollY() == 0) {
                    return true;
                } else if (deltaY < 0
                        && child.getMeasuredHeight() <= getHeight()
                        + mScrollView.getScrollY()) {
                    return true;
                }
            }
            return false;
        }
    
        /** * header 准备刷新,手指移动过程,还没有释放 * * @param deltaY ,手指滑动的距离 */ private void headerPrepareToRefresh(int deltaY) {
            int newTopMargin = changingHeaderViewTopMargin(deltaY);
        }
    
        private int changingHeaderViewTopMargin(int deltaY) {
            LayoutParams params = (LayoutParams) mHeaderView.getLayoutParams();
            float newTopMargin = params.topMargin + deltaY * 0.3f;
            params.topMargin = (int) newTopMargin;
            mHeaderView.setLayoutParams(params);
            invalidate();
            return params.topMargin;
        }
    
        /** * 设置header view 的topMargin的值 */ private void setHeaderTopMargin(int topMargin) {
            LayoutParams params = (LayoutParams) mHeaderView.getLayoutParams();
            params.topMargin = topMargin;
            mHeaderView.setLayoutParams(params);
            invalidate();
        }
    
        private int getHeaderTopMargin() {
            LayoutParams params = (LayoutParams) mHeaderView.getLayoutParams();
            return params.topMargin;
        }
    }

致敬海大爷