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);
        }
    }

}

recyclerView在设置适配器之后

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

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