預(yù)期效果

類似魅族便簽下拉顯示標(biāo)題的效果，加入了顯示隱藏的動畫。

實(shí)現(xiàn)

1、OnLayout中獲取第一個子view的高度

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        mChildLayout = (ViewGroup) getChildAt(0);
        mTopChildView = mChildLayout.getChildAt(0);
        topChildHeight = mTopChildView.getMeasuredHeight();
        screenHeight = getMeasuredHeight();
        offsetDistance = topChildHeight - screenHeight;
        if (!mInited) {
            mInited = true;
            if (currentPage == PAGE_BOTTOM) {
                scrollTo(0, topChildHeight);
            }
        }
    }

2、dispatchTouchEvent中在ACTION_UP時，通過getscrollY()即當(dāng)前滑動的距離與header View高度的比較，并設(shè)定一個閾值，當(dāng)getscrollY()大于或小于該閾值時，顯示或隱藏header view。

@Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (isInIgnoredView(ev)) {
            //往下傳遞
            Log.e(TAG, "dispatchTouchEvent>>傳遞事件");
            return super.dispatchTouchEvent(ev);
        } else {
            Log.e(TAG, "dispatchTouchEvent>>不傳遞事件");
            switch (ev.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    isTouch = true;
                    downY = (int) ev.getY();
                    downTime = System.currentTimeMillis();
                    if (mScroller != null) {
                        mScroller.forceFinished(true);
                        mScroller = null;
                    }
                    break;
                case MotionEvent.ACTION_MOVE:

                    break;
                case MotionEvent.ACTION_UP:
                    isTouch = false;
                    upY = (int) ev.getY();
                    upTime = System.currentTimeMillis();
                    boolean isUpMove = upY - downY <= 0;//是否上劃
                    //用戶手指在屏幕上的時間
                    long duration = upTime - downTime;

                    //這里要確保點(diǎn)擊事件不失效
                    //we force stop scroll when touch down
                    //in some case we need to finish scroll up or down
                    if (currentPage == PAGE_TOP) {
                        //下面的判斷已經(jīng)能確定用戶是否往上滑
                        if (getScrollY() > offsetDistance) {
                            mScroller = new Scroller(mContext);
                            if (getScrollY() < (screenHeight * PERCENT + offsetDistance) && duration > TOUCH_DURATION) {
                                //基本可以無視
                                isPageChange = false;
                                scrollToTarget(PAGE_TOP);
                            } else if (getScrollY() > topChildHeight / 5) {
                                //切換到下界面 手勢是上劃且滑動的距離大于一定值
                                isPageChange = true;
                                scrollToTarget(PAGE_BOTTOM);

                            } else if (getScrollY() <= topChildHeight / 5) {
                                isPageChange = false;
                                scrollToTarget(PAGE_TOP);
                            } else if (getScrollY() > topChildHeight) {
                                isPageChange = true;
                                currentPage = PAGE_BOTTOM;
                            }
                            return false;
                        }
                    } else {
                        if (getScrollY() < topChildHeight) {
                            mScroller = new Scroller(mContext);
                            if (getScrollY() < topChildHeight / 2) {
                                //切換到上界面
                                isPageChange = true;
                                scrollToTarget(PAGE_TOP);
                            } else {
                                isPageChange = false;
                                scrollToTarget(PAGE_BOTTOM);
                            }
                            return false;
                        }
                    }

                    break;
            }
        }

        return super.dispatchTouchEvent(ev);
    }

3、header view設(shè)置粘性滑動(有沒有更貼切的名字？) 即scrollview的滑動不跟隨手指的滑動，假如設(shè)置的比值為0.4，那么手指滑動10個像素，實(shí)際scrollview只滑動了4個像素，類似下拉刷新的那種下拉吃力的感覺。實(shí)現(xiàn)方法很簡單，在TouchEvent中，通過scrollBy()方法實(shí)現(xiàn)scrollview的滑動，并返回true，表示scrollview消費(fèi)了該次事件。

  @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (isInIgnoredView(ev)) {
            Log.e(TAG, "onTouchEvent>>不消費(fèi)事件");
            return false;
        } else {
            Log.e(TAG, "onTouchEvent>>消費(fèi)事件");
            currentY = (int) ev.getY();
            switch (ev.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    lastY = (int) ev.getY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    int moveY = currentY - lastY;
                    lastY = currentY;
                    if (currentPage == PAGE_BOTTOM) {
                        if (getScrollY() <= topChildHeight) {
                            //下拉
                            scrollBy(0, (int) (-moveY * mFraction));
                            return true;
                        } else {
                            return super.onTouchEvent(ev);
                        }
                    } else {
                        return super.onTouchEvent(ev);
                    }
                case MotionEvent.ACTION_CANCEL:
                case MotionEvent.ACTION_UP:
                    break;
            }
            return super.onTouchEvent(ev);
        }
    }

4、動畫。動畫使用了屬性動畫，這里就不多介紹了。

效果圖

gif太大..簡書上傳不了.
偷偷懶，移步github看效果

GitHub

github源碼

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