   @Override
    public void addView(View child, ViewGroup.LayoutParams params) {
        super.addView(child, params);
        Bounds bounds = getBunds(getChildCount());
    }

確保每個子View的測量屬性寬度填滿父組件

    boolean mesured = false;
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mesured == true) {//只需要測量一次
            return;
        }
        mesured = true;
        int childCount = getChildCount();
        int rootWidth = getWidth();
        int rootHeight = getHeight();
        if (childCount > 0) {
            View child0 = getChildAt(0);
            int modeWidth = MeasureSpec.getMode(child0.getMeasuredWidth());
            int sizeWidth = MeasureSpec.getSize(child0.getMeasuredWidth());

            int modeHeight = MeasureSpec.getMode(child0.getMeasuredHeight());
            int sizeHeight = MeasureSpec.getSize(child0.getMeasuredHeight());

            if (childCount > 0) {
                for (int i = 0; i < childCount; i++) {
                    View childView = getChildAt(i);
                    childView.measure(MeasureSpec.makeMeasureSpec(sizeWidth, MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(sizeHeight, MeasureSpec.EXACTLY));
                    int top = (int) (i * (sizeHeight * carEvPercnet));
                    getBunds(i).setTop(top);
                    getBunds(i).setCurrentTop(top);
                    getBunds(i).setLastCurrentTop(top);
                    getBunds(i).setHeight(sizeHeight);
                }

            }

        }
    }

重寫onLayout 方法是關鍵

是動畫觸發(fā)的主要目的，這里layout參數(shù)并不是寫死的，而是計算出來的（通過ValueAnimator 計算出來的）

@Override
    protected void onLayout(boolean changed, int sl, int st, int sr, int sb) {
        int childCount = getChildCount();
        if (childCount > 0) {
            for (int i = 0; i < childCount; i++) {
                View view = getChildAt(i);
                int mWidth = view.getMeasuredWidth();
                int mw = MeasureSpec.getSize(mWidth);
                int l = 0, r = l + mw;
                view.layout(l, getBunds(i).getCurrentTop(), r, getBunds(i).getCurrentTop() + getBunds(i).getHeight());
            }
        }
    }