RecyclerView实现抖音纵向滚动ViewPager效果

class MyLinearLayoutManager : LinearLayoutManager {  private lateinit var mPagerSnapHelper: PagerSnapHelper  private var mOnViewPagerListener: OnViewPagerListener? = null  private lateinit var mRecyclerView: RecyclerView  private var mDrift: Int = 0//位移，用来判断移动方向  constructor(context: Context) : this(context, OrientationHelper.VERTICAL)  constructor(context: Context, orientation: Int) : this(context, orientation, false)  constructor(context: Context, orientation: Int, reverseLayout: Boolean) : super(context, orientation, reverseLayout) {    mPagerSnapHelper = PagerSnapHelper()  }  override fun onAttachedToWindow(view: RecyclerView) {    super.onAttachedToWindow(view)    mPagerSnapHelper.attachToRecyclerView(view)//设置RecyclerView每次滚动一页    mRecyclerView = view    mRecyclerView.addOnChildAttachStateChangeListener(mChildAttachStateChangeListener)  }  /**   * 滑动状态的改变   * 缓慢拖拽-> SCROLL_STATE_DRAGGING   * 快速滚动-> SCROLL_STATE_SETTLING   * 空闲状态-> SCROLL_STATE_IDLE   * @param state   */  override fun onScrollStateChanged(state: Int) {    if (state == RecyclerView.SCROLL_STATE_IDLE){      val viewIdle = mPagerSnapHelper.findSnapView(this)      val positionIdle = getPosition(viewIdle!!)      if (mOnViewPagerListener != null && childCount == 1) {        mOnViewPagerListener!!.onPageSelected(positionIdle, positionIdle == itemCount - 1)      }    }  }  /**   * 布局完成后调用   * @param state   */  override fun onLayoutCompleted(state: RecyclerView.State?) {    super.onLayoutCompleted(state)    if (mOnViewPagerListener != null) mOnViewPagerListener!!.onLayoutComplete()  }  /**   * 监听竖直方向的相对偏移量   */  override fun scrollVerticallyBy(dy: Int, recycler: RecyclerView.Recycler?, state: RecyclerView.State?): Int {    this.mDrift = dy    return super.scrollVerticallyBy(dy, recycler, state)  }  /**   * 监听水平方向的相对偏移量   */  override fun scrollHorizontallyBy(dx: Int, recycler: RecyclerView.Recycler?, state: RecyclerView.State?): Int {    this.mDrift = dx    return super.scrollHorizontallyBy(dx, recycler, state)  }  /**   * 设置监听   * @param listener   */  fun setOnViewPagerListener(listener: OnViewPagerListener) {    this.mOnViewPagerListener = listener  }  private val mChildAttachStateChangeListener = object : RecyclerView.OnChildAttachStateChangeListener {    override fun onChildViewAttachedToWindow(view: View) {    }    override fun onChildViewDetachedFromWindow(view: View) {      if (mDrift >= 0) {        if (mOnViewPagerListener != null) mOnViewPagerListener!!.onPageRelease(true, getPosition(view))      } else {        if (mOnViewPagerListener != null) mOnViewPagerListener!!.onPageRelease(false, getPosition(view))      }    }  }  interface OnViewPagerListener{    /*释放的监听*/    fun onPageRelease(isNext: Boolean, position: Int)    /*选中的监听以及判断是否滑动到底部*/    fun onPageSelected(position: Int, isBottom: Boolean)    /*布局完成的监听*/    fun onLayoutComplete()  }}

class MyImageView : ImageView {  constructor(context: Context) : this(context, null!!)  constructor(context: Context, attr: AttributeSet) : this(context, attr, 0)  constructor(context: Context, attr: AttributeSet, defStyleAttr: Int) : super(context, attr, defStyleAttr)  override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {    val width = View.getDefaultSize(0, widthMeasureSpec)    val height = View.getDefaultSize(0, heightMeasureSpec)    setMeasuredDimension(width, height)  }}