recyclerview实现卡片滑动效果

想recyclerview快速实现卡片滑动，需要一个重要帮助类，LinearSnapHelper类,这个类是Android24.2.0之后引入的帮助类，是SnapHelper抽象类的子类

具有让recyclerview中的item居中的功能，实现也相当简单
LinearSnapHelper linearSnapHelper = new LinearSnapHelper();
linearSnapHelper.attachToRecyclerView(recycler);
相比于通过viewpager然后监听viewpager的滑动，实现要简单一点

设置linearsnahelper只能让item选为居中，没有卡片滑动效果，接下来如果实现？

第一步：item的宽度，设置左右margin边距，让item左右有空白间隙；

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
 View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.my_recyclerview_item,parent,false);
 //这里设置view的宽度
 RecyclerScaleUtils.onCreateViewHolder(parent,view,ScreenUtil.dip2px(parent.getContext(),30f));
 return new MyViewHolder(view);
}
RecyclerScaleUtils类中的onCreateViewHolder方法，就是设置item的宽度 
public static void onCreateViewHolder(ViewGroup parent, View itemView,int margin) {
    RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) itemView.getLayoutParams();
    if(margin <= 0){
        margin = mDefaultMargin;
    }
    lp.width = parent.getWidth() - 2*margin;
    itemView.setLayoutParams(lp);
 


 @Overridepublic void onBindViewHolder(MyViewHolder holder, int position) { //设置第一个与最后item对称显示 RecyclerScaleUtils.onBindViewHolder(holder.itemView,position, getItemCount(),ScreenUtil.dip2px(holder.itemView.getContext(),30f)); Glide.with(mContext).load(mList.get(position)).centerCrop().into(holder.mImageview);}
//这里是处理最左边和最右边的宽度public static void onBindViewHolder(View itemView, final int position, int itemCount,int margin) { int leftMarin = 0; int rightMarin = 0; int topMarin = 0; int bottomMarin = 0; if(position == 0){ leftMarin = margin; rightMarin = 0; }else if(position == (itemCount-1)){ leftMarin = 0; rightMarin = margin; } ViewGroup.MarginLayoutParams lp = (ViewGroup.MarginLayoutParams) itemView.getLayoutParams(); if (lp.leftMargin != leftMarin || lp.topMargin != topMarin || lp.rightMargin != rightMarin || lp.bottomMargin != bottomMarin) { lp.setMargins(leftMarin, topMarin, rightMarin, bottomMarin); itemView.setLayoutParams(lp); } }

第二步：就是在左右滑动的时候，当前item，和左右item都有相应的缩放效果；如左滑，当前item缩小，右边item，放大（这里可以用动画）

public void attachToRecyclerView(RecyclerView recyclerView,int margin){
 if(recyclerView == null){
 return;
 }
 mRecycler = recyclerView;
 if(margin <= 0){
 mMargin = mDefaultMargin;
 }else {
 mMargin = margin;
 }
 initView();
 final CustomLinearSnapHelper helper = new CustomLinearSnapHelper();
 recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
 @Override
 public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
 super.onScrollStateChanged(recyclerView, newState);
 if(newState == RecyclerView.SCROLL_STATE_IDLE){
 if(mDistances == 0 || mDistances == (mItemCount*mItemwidth)){
 helper.mStateIdle = true;
 }else{
 helper.mStateIdle = false;
 }
 }
 }

 @Override
 public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
 super.onScrolled(recyclerView, dx, dy);
 if(recyclerView.getLayoutManager().getLayoutDirection() == LinearLayoutManager.HORIZONTAL){
 mDistances += dx;
 getCurrentPosition();
 setItemScale();
 }

 }
 });

 helper.attachToRecyclerView(recyclerView);
}
//这里获取item的宽与countitem数
protected void initView( ){
 mRecycler.post(new Runnable() {

 @Override
 public void run() {
 mItemCount = mRecycler.getAdapter().getItemCount();
 mItemwidth = mRecycler.getWidth() - 2 * mMargin;
 mRecycler.smoothScrollToPosition(mCurrentPosition);
 setItemScale();
 }
 });
}
//item在滑动时，进行动画的缩放
public void setItemScale(){
 View leftView = null;
 View rightView = null;
 if(mCurrentPosition > 0){
 leftView = mRecycler.getLayoutManager().findViewByPosition(mCurrentPosition - 1);
 }
 View currentView = mRecycler.getLayoutManager().findViewByPosition(mCurrentPosition);
 if(mCurrentPosition <(mItemCount - 1)){
 rightView = mRecycler.getLayoutManager().findViewByPosition(mCurrentPosition +1);
 }

 //滑动百分比，左右的都是放大，中间缩小
 float percent = Math.abs((mDistances - mCurrentPosition * mItemwidth*1.0f)/mItemwidth);

 if(leftView != null){
 //这里是缩小原来大小的0.8-1.0 左右0.8，中间1.0 0.8+(percent*0.2)
 leftView.setScaleY(0.8f+(percent*0.2f));
 }
 if(currentView != null){
 currentView.setScaleY(1-0.2f*percent);
 }
 if(rightView != null){
 rightView.setScaleY(0.8f+(percent*0.2f));
 }

}
protected void getCurrentPosition(){
 if(mItemwidth <= 0) return;
 boolean change = false;

 if (Math.abs(mDistances - mCurrentPosition * mItemwidth) >= mItemwidth) {
 change = true;
 }
 if (change) { //这里是从0开始的
 mCurrentPosition = mDistances / mItemwidth;
 }

}
public static void setItemPosition(int position){
 this.mCurrentPosition = position;
 this.mDistances = position * mItemwidth;
}
这里自定义了linearsanphelper,因为在第一个item和最后一个item设置了marginleft与rightmargin，导致这两个item的
中心位置滑动的偏移，此时LinearSnapHelper通过调用recyclerview的onscrolllistener获取不动具体的中心点，而误以为
客户一直在滑动，
   
public class CustomLinearSnapHelper extends LinearSnapHelper { public static boolean mStateIdle = false; /** // * int[] snapDistance = calculateDistanceToFinalSnap(layoutManager, snapView); // if (snapDistance[0] != 0 || snapDistance[1] != 0) { // mRecyclerView.smoothScrollBy(snapDistance[0], snapDistance[1]); // } // 这个方法返回的数组值，是让recyclerview移动并居中显示的,如果是第一个或者最后一个位置， // 因无法居中而调用recyclerview的OnScrollListener监听 // */ @Override public int[] calculateScrollDistance(int velocityX, int velocityY) { if(mStateIdle){ return new int[2]; }else{ int[] ints = super.calculateScrollDistance(velocityX, velocityY); for (int i:ints){ Log.e("tests","==i=="+i); } return super.calculateScrollDistance(velocityX, velocityY); } }}

RecyclerScaleUtils utils = new RecyclerScaleUtils();
utils.attachToRecyclerView(recycler,ScreenUtil.dip2px(this,30f));

demo链接http://download.csdn.net/detail/change987654321/9689690