recyclerview 滚动状态

RecyclerView 有三种滚动状态：

第一种：静止状态，滚动结束后回到此状态

/**
     * The RecyclerView is not currently scrolling.
     * @see #getScrollState()
     */
    public static final int SCROLL_STATE_IDLE = 0;

第二种：拖动状态，手指按在屏幕上拖动时的状态
    /**
     * The RecyclerView is currently being dragged by outside input such as user touch input.
     * @see #getScrollState()
     */
    public static final int SCROLL_STATE_DRAGGING = 1;

第三种：滑行状态，手指已离开屏幕，但仍在滚动的状态
    /**
     * The RecyclerView is currently animating to a final position while not under
     * outside control.
     * @see #getScrollState()
     */
    public static final int SCROLL_STATE_SETTLING = 2;