探探效果：
demo效果如下：
LayoutManager自定义
对于自定义LayoutManager我们主要处理好三件事情，就所有的问题就都迎刃而解了:
布局每个ItemView
处理滑动事件
缓存重用ItemView
LayoutManager自定义时常用函数介绍
这里定义RecyclerView里面每个item默认的LayoutParams
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
}
重写这个函数来布局RecyclerView当前需要显示的item,确定每个item的位置
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
super.onLayoutChildren(recycler, state);
//TODO:来布局RecyclerView当前需要显示的item
}
处理滑动需要重写的函数：
//是否可以水平滑动
@Override
public boolean canScrollHorizontally() {
return true;
}
//canScrollHorizontally返回true的基础上，RecyclerView有手指水平滑动的时候回调
//该函数 * 注意处理完之后要返回消费的距离
@Override
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state) {
//TODO:滑动逻辑
return dx;
}
//是否可以垂直滑动
@Override
public boolean canScrollVertically() {
return true;
}
//canScrollVertically返回true的基础上，RecyclerView有手指垂直滑动的时候回调该函数 * 注意处理完之后要返回消费的距离
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
//TODO:滑动逻辑
return dy;
}
缓存重用ItemView
/* detach轻量回收View */
detachAndScrapAttachedViews(recycler);
detachAndScrapView(view, recycler);
/** * recycle真的回收一个View ，该View再次回来需要执行onBindViewHolder方法 */
removeAndRecycleView(View child, Recycler recycler)
removeAndRecycleAllViews(Recycler recycler);
/** * 超级轻量回收一个View,马上就要添加回来,和attachView()对应 */
detachView(view);
/** * 将detachView(view) detach的View attach回来 */
attachView(view);
/** * detachView 后 没有attachView的话 就要真的回收掉他们 */
recycler.recycleView(viewCache.valueAt(i));
步骤一：写一个普通recyclerView垂直列表。
步骤二：自定义LayoutManager，重写onLayoutChildren自行处理子view位置，根据position不同处理各自的大小和偏移。
public class SlideCardLayoutManager extends RecyclerView.LayoutManager {
private final int MAX_CARD_COUNT = 4;
private final float SCALE_RATIO = 0.08f;
private final float TRANSITION_Y = 30f;
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
}
//必须要重写，对item设置放置规则
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
//直接使用父类的回收功能
detachAndScrapAttachedViews(recycler);
int itemCount = getItemCount(); //当前adapter中总共item数
int bottomPosition;
if (itemCount < MAX_CARD_COUNT) {
bottomPosition = 0;
} else {
bottomPosition = itemCount - MAX_CARD_COUNT;
}
//遍历最下层position到最上层postion的view
for (int i=bottomPosition;i<itemCount;i++) {
//复用缓存view，底层就是使用了 tryGetViewHolderForPositionByDeadline
View view = recycler.getViewForPosition(i);
addView(view); //将itemView添加到recyclerView中
measureChildWithMargins(view, 0, 0); //测量itemView
//view在RecyclerView里面还剩余的宽度、高度空隙
int viewWidth = getDecoratedMeasuredWidth(view);
int viewHeight = getDecoratedMeasuredHeight(view);
int widthSpace = getWidth() - viewWidth;
int heightSpace = getHeight() - viewHeight;
//布局itemView，把所有itemView放在屏幕正中
layoutDecoratedWithMargins(view, widthSpace/2, heightSpace/2,
widthSpace/2+ viewWidth, heightSpace/2 + viewHeight);
//从下到上定义level
int level = itemCount - i - 1;
if (level < MAX_CARD_COUNT) {
//对itemView进行y方向平移
view.setTranslationY(TRANSITION_Y*level);
//对itemView进行放大
view.setScaleX(1-SCALE_RATIO*level);
} else {
//如果是最底下一张，则效果与前一张一样，即不会展示出来
view.setTranslationY(TRANSITION_Y*(level-1));
view.setScaleX(1-SCALE_RATIO*(level-1));
}
}
}
}
使用该layoutManager，就可以实现从小到大层叠放置卡片效果了，只是，这个时候没有拖动事件。
步骤三：自定义ItemTouchHelper，重写onChildDraw方法，在拖拽过程中遍历子view做放大效果。
public class SlideCardCallBack extends ItemTouchHelper.SimpleCallback {
private RecyclerView.Adapter adapter;
private ArrayList datas;
private final float SCALE_RATIO = 0.08f;
private final float TRANSITION_Y = 30f;
/**
* 构造方法设置可滑动方向，上下左右 0x1111，参数一：拖拽 参数er：滑动
* public static final int UP = 1;
* public static final int DOWN = 1 << 1;
* public static final int LEFT = 1 << 2;
* public static final int RIGHT = 1 << 3;
*/
public SlideCardCallBack(RecyclerView.Adapter adapter, ArrayList datas) {
super(0, 15); //15表示支持各个方向拖拽
this.adapter = adapter;
this.datas = datas;
}
@Override
public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
return false;
}
//滑动动画结束后的操作
@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
//这里需要将最顶层滑出去的data移除，然后添加到最底层，保证切换能循环进行
Object remove = datas.remove(viewHolder.getLayoutPosition());
datas.add(0, remove);
adapter.notifyDataSetChanged();
}
//绘制拖拽过程中方法的效果
@Override
public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
//dx dy分别表示当前拖拽view相对于原来横纵坐标偏移
double distance = Math.sqrt(dX*dX+dY*dY);
double maxDistance = recyclerView.getWidth() * 0.5f;
double fraction = distance / maxDistance; //偏移放大系数
if (fraction > 1) {
fraction = 1; //放大系数最大为1
}
//遍历，为每个child执行动画
int itemCount = recyclerView.getChildCount();
for (int i=0;i<itemCount;i++) {
//在动画渐变的过程中，最大达到它上面一个卡片的大小
View view = recyclerView.getChildAt(i);
int level = itemCount - i - 1;
view.setTranslationY((float) (TRANSITION_Y*level-fraction*TRANSITION_Y));
view.setScaleX((float) (1-SCALE_RATIO*level+ fraction*SCALE_RATIO));
}
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}
//设置滑动不生效回弹距离
@Override
public float getSwipeThreshold(@NonNull RecyclerView.ViewHolder viewHolder) {
return 0.2f;
}
}
给recyclerView设置ItemTouchHelper，设置拖拽事件，并在拖拽过程中，将每一个子view做放大处理。
MainActivity代码:
class MainActivity : AppCompatActivity() {
private var recyclerView: RecyclerView?= null
private var adapter: CardAdapter?= null
private var datas = ArrayList<CardBean>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
recyclerView = findViewById(R.id.recyclerview)
adapter = CardAdapter(applicationContext)
recyclerView?.layoutManager = SlideCardLayoutManager()
recyclerView?.adapter = adapter
initDatas()
}
private fun initDatas() {
datas.add(CardBean(R.mipmap.wanghong1))
datas.add(CardBean(R.mipmap.wanghong2))
datas.add(CardBean(R.mipmap.wanghong3))
datas.add(CardBean(R.mipmap.wanghong4))
datas.add(CardBean(R.mipmap.wanghong5))
datas.add(CardBean(R.mipmap.wanghong6))
adapter?.setDatas(datas)
ItemTouchHelper(SlideCardCallBack(adapter, datas)).attachToRecyclerView(recyclerView)
}
}
Adapter代码：
class CardAdapter(val context: Context): RecyclerView.Adapter<CardAdapter.CardViewHolder>() {
private var datas = ArrayList<CardBean>()
fun setDatas(datas: ArrayList<CardBean>) {
this.datas = datas
notifyDataSetChanged()
}
class CardViewHolder(itemView: View) : ViewHolder(itemView) {
var imageView:ImageView?= null
init {
imageView = itemView.findViewById(R.id.iv_cover)
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CardViewHolder {
return CardViewHolder(LayoutInflater.from(context).inflate(R.layout.item, parent, false))
}
override fun onBindViewHolder(holder: CardViewHolder, position: Int) {
holder.imageView?.setImageResource(datas[position].coverRes)
}
override fun getItemCount() = datas.size
}
