RecyclerView正确使用notify（notifyIte

一款Android App能不能告诉我你不使用RecyclerView（这个好像可以有），这个应该很少了吧。那么数据刷新是不是还是一个notifyDataSetChanged()一刷到底呢 ？在适配器的刷新方法里，其实还有这么几个常用的 notify，

1. 刷新全部的item，notifyDataSetChanged()   
2. 刷新指定的item，notifyItemChanged(int)   
3. 从指定的位置开始刷新指定个item，notifyItemRangeChanged(int,int) 这个刷新onBindViewHolder方法，position才能保持一直
4. 插入、移动指定位置的item，并刷新，notifyItemInserted(int)、notifyItemMoved(int)、notifyItemRemoved(int)  （有坑记得要填）
5. 局部刷新指定的数据，notifyItemChanged(int, Object)

正题：demo测试几个刷新，且填坑。
界面图长这样

Screenrecord-2019-07-27-23-38-08-547_20190727235031

简单实现的adapter

/**
 * author: kun .
 * date:   On 2019/7/25
 */
public class RVAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private List<Data> mDataList;
private Context mContext;

public RVAdapter(List<Data> dataList, Context context) {
    mDataList = dataList;
    mContext = context;
}

@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    View view= LayoutInflater.from(mContext).inflate(R.layout.rv_item_layout,null);
    return new RVHolder(view);
}

@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, final int position) {
    if(viewHolder instanceof RVHolder){
        final Data data = mDataList.get(position);
        ((RVHolder) viewHolder).mTvName.setText(data.getName());
        ((RVHolder) viewHolder).mTvDes.setText(data.getDes());
        Glide.with(mContext).load(data.image).placeholder(R.mipmap.ic_launcher).into(((RVHolder) viewHolder).mImageView);
        viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(mContext, "name:"+data.getName()+" pos:"+position, Toast.LENGTH_SHORT).show();
            }
        });
    }
}

@Override
public int getItemCount() {
    return mDataList.size();
}

class RVHolder extends RecyclerView.ViewHolder{
    ImageView mImageView;
    TextView mTvName,mTvDes;
    public RVHolder(@NonNull View itemView) {
        super(itemView);
        mImageView=itemView.findViewById(R.id.iv_image);
        mTvName=itemView.findViewById(R.id.tv_name);
        mTvDes=itemView.findViewById(R.id.tv_des);
    }
}
}

测试用例，简单布局
在Activity里的调用如下：
1.一键傻瓜式刷新

Screenrecord-2019-07-27-23-38-08-547_20190727235031

 mDataList.addAll(addData());
 mRvAdapter.notifyDataSetChanged();

notifyDataSetChanged()一键刷新，解决80%的刷新问题，刷新走一波

2.一键移除花式刷新

Screenrecord-2019-07-27-23-38-08-547_20190727235031.gif

    mRvAdapter.notifyItemRemoved(1);
    mDataList.remove(1);
    //受影响的item都刷新position
    mRvAdapter.notifyItemRangeChanged(1, mDataList.size() - 1);

notifyItemRemoved(int)指定移除某个item，mDataList数据一定要同步更新,否者RecyclerView会报错,(坑记得要填)notifyItemRangeChanged(1, mDataList.size() - 1)记得调用（不信可以试试不调用的后果），否者在点击的时候position仍然是移除之前的position，notifyItemRangeChanged会刷新notifyItemRangeChanged方法，保证position的准确位置，刷新后的position与数据相匹配。notifyItemRemoved(int)自带刷新动画，花式移除item.
3.一键插入花式刷新

Screenrecord-2019-07-27-23-38-08-547_20190727235249.gif

Data data=new Data();
data.setName("name:"+"插入");
data.setDes("des:"+"插入");
data.setImage(refreshImage);
mDataList.add(1,data);
mRvAdapter.notifyItemInserted(1);  
mRvAdapter.notifyItemRangeChanged(1, mDataList.size() + 1);

notifyItemInserted(int)花式插入数据，与一键移除花式刷新差不多，同时notifyItemRangeChanged(1, mDataList.size() + 1)千万别忘了，否者会有多个item同一个position（后果很严重的哦）。
4.一键移花接木式刷新

Screenrecord-2019-07-27-23-38-08-547_20190727235516.gif

     //注意位置的变换 1 和 4 交换
     Data remove4 = mDataList.remove(4);
     Data remove1 = mDataList.remove(1);
     mDataList.add(1,remove4);
     mDataList.add(4,remove1);
     mRvAdapter.notifyItemMoved(4,1);
     //受影响的item都刷新position
      mRvAdapter.notifyItemRangeChanged(Math.min(4, 1), Math.abs(4 - 1) +1);//受影响的item都刷新position

notifyItemMoved(int fromPosition, int toPosition)带动画的移动item，从指定位置到指定位置的移动，数据更新加移动动画，同样notifyItemRangeChanged(Math.min(4, 1), Math.abs(4 - 1) +1)同样的作用，忘记调用会吃大亏。

5.一键指定刷新

Screenrecord-2019-07-27-23-38-08-547_20190727235707.gif

            Data data1=new Data();
            data1.setImage(refreshImage);
            mDataList.get(1).setImage(refreshImage);
            mRvAdapter.notifyItemChanged(1,data1);

---

Screenrecord-2019-07-27-23-38-08-547_20190727235758.gif

            mDataList.get(1).setImage(refreshImage);
            mRvAdapter.notifyItemChanged(1);

局部刷新notifyItemChanged(int position),notifyItemChanged(int position,Object payload),两个方法都是局部刷新的方法，RecyclerView特色刷新方式，指定位置进行刷新，比如item有进度条数据，这种数据变化频繁，或者聊天界面都会使用局部刷新。

6.自定义局部刷新

Screenrecord-2019-07-27-23-38-08-547_20190728000202.gif

//获取到viewholder的view
    View viewHolder = mGridLayoutManager.findViewByPosition(3);
    mDataList.get(3).setImage(notifyImage);
    ImageView imageView=viewHolder.findViewById(R.id.iv_image);
    Glide.with(this).load(notifyImage).placeholder(R.mipmap.ic_launcher).into(imageView);

通过mGridLayoutManager.findViewByPosition(3)布局管理器，可以获取到指定的item，获取到指定的View，就可以实现对这个View的操作。实现刷新

Activity的完整代码

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

private RecyclerView mRvList;
private List<Data> mDataList=new ArrayList<>();
private String image="http://ww3.sinaimg.cn/large/610dc034gw1f9shm1cajkj20u00jy408.jpg";
private String refreshImage="http://ww3.sinaimg.cn/large/610dc034jw1fa2vh33em9j20u00zmabz.jpg";
private String notifyImage="http://ww2.sinaimg.cn/large/610dc034jw1f9vyl2fqi0j20u011habc.jpg";
private Button mBtNotify_1;
private Button mBtNotify_2;
private Button mBtNotify_3;
private Button mBtNotify_4;
private Button mBtNotify_5;
private Button mBtNotify_6;
private Button mBtNotify_7;
private RVAdapter mRvAdapter;
private GridLayoutManager mGridLayoutManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initView();
    initListener();
}

private void initView() {
    mRvList = findViewById(R.id.recyclerview);
    mBtNotify_1 = findViewById(R.id.bt_notify_1);
    mBtNotify_2 = findViewById(R.id.bt_notify_2);
    mBtNotify_3 = findViewById(R.id.bt_notify_3);
    mBtNotify_4 = findViewById(R.id.bt_notify_4);
    mBtNotify_5 = findViewById(R.id.bt_notify_5);
    mBtNotify_6 = findViewById(R.id.bt_notify_6);
    mBtNotify_7 = findViewById(R.id.bt_notify_7);
    mGridLayoutManager = new GridLayoutManager(this,2);
    mRvList.setLayoutManager(mGridLayoutManager);
    mRvAdapter = new RVAdapter(mDataList,this);
    mRvList.setAdapter(mRvAdapter);
    initData();
    mRvAdapter.notifyDataSetChanged();
}

private void initData() {
    for (int i = 0; i < 10; i++) {
        Data data=new Data();
        data.setName("name:"+i);
        data.setDes("desc:"+i);
        data.setImage(image);
        mDataList.add(data);
    }
}

private void initListener() {
    mBtNotify_1.setOnClickListener(this);
    mBtNotify_2.setOnClickListener(this);
    mBtNotify_3.setOnClickListener(this);
    mBtNotify_4.setOnClickListener(this);
    mBtNotify_5.setOnClickListener(this);
    mBtNotify_6.setOnClickListener(this);
    mBtNotify_7.setOnClickListener(this);
    mRvList.setOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
        }

        @Override
        public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            int firstVisibleItemPosition = mGridLayoutManager.findFirstCompletelyVisibleItemPosition();
            int lastVisibleItemPosition = mGridLayoutManager.findLastCompletelyVisibleItemPosition();
            for (int i = firstVisibleItemPosition; i <lastVisibleItemPosition; i++) {
                View view = mGridLayoutManager.findViewByPosition(i);
                ImageView imageView=view.findViewById(R.id.iv_image);
                //可实现可见item的动画，而不是绘制item的动画，滑动就会触发动画
//              setAnimation(imageView);
            }
        }
    });
}

@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.bt_notify_1:
            mDataList.addAll(addData());
            mRvAdapter.notifyDataSetChanged();
            break;
        case R.id.bt_notify_2:
            mDataList.remove(1);
            mRvAdapter.notifyItemRemoved(1);
            //受影响的item都刷新position
            mRvAdapter.notifyItemRangeChanged(1, mDataList.size() - 1);
            //批量删除
            //mRvAdapter.notifyItemRangeRemoved(int positionStart, int itemCount)
            break;
        case R.id.bt_notify_3:
            Data data=new Data();
            data.setName("name:"+"插入");
            data.setDes("des:"+"插入");
            data.setImage(refreshImage);
            mDataList.add(1,data);
            mRvAdapter.notifyItemInserted(1);
            mRvAdapter.notifyItemRangeChanged(1, mDataList.size() + 1);
            break;
        case R.id.bt_notify_4:
            //注意位置的变换 1 和 4 交换
            Data remove4 = mDataList.remove(4);
            Data remove1 = mDataList.remove(1);
            mDataList.add(1,remove4);
            mDataList.add(4,remove1);
            mRvAdapter.notifyItemMoved(4,1);
            //受影响的item都刷新position
            mRvAdapter.notifyItemRangeChanged(Math.min(4, 1), Math.abs(4 - 1) +1);//受影响的item都刷新position
            break;
        case R.id.bt_notify_5:
            Data data1=new Data();
            data1.setImage(refreshImage);
            mDataList.get(1).setImage(refreshImage);
            mRvAdapter.notifyItemChanged(1,data1);
            break;
        case R.id.bt_notify_6:
            mDataList.get(1).setImage(refreshImage);
            mRvAdapter.notifyItemChanged(1);
            break;
        case R.id.bt_notify_7:
            //获取到viewholder的view
            View viewHolder = mGridLayoutManager.findViewByPosition(3);
            mDataList.get(3).setImage(notifyImage);
            ImageView imageView=viewHolder.findViewById(R.id.iv_image);
            Glide.with(this).load(notifyImage).placeholder(R.mipmap.ic_launcher).into(imageView);
            break;
    }
}

private List<Data> addData(){
    List<Data> datalist=new ArrayList<>();
    for (int i = 0; i < 6; i++) {
        Data data=new Data();
        data.setName("name:"+"refresh-"+i);
        data.setDes("des:"+"refresh-"+i);
        data.setImage(notifyImage);
        datalist.add(data);
    }
    return datalist;
}

public void setAnimation(View view) {
    ObjectAnimator mObjectAnimator = ObjectAnimator.ofFloat(view, "rotation", -6, 6,6,-6,0);
    mObjectAnimator.setDuration(500);
    mObjectAnimator.setRepeatCount(1);
    mObjectAnimator.setInterpolator(new AccelerateInterpolator());
    mObjectAnimator.start();
}
}