RecyclerView学习笔记

Posted 2022-11-13 Cokernut_林

Github  个人主页

RecyclerView是Google在发布android L时在support-v7包中添加的一个新组件，旨在用来替代ListView。RecyclerView的灵活性要比ListView更好。

RecyclerView与ListView原理是类似的：都是仅仅维护少量的View并且可以展示大量的数据集。RecyclerView用以下两种方式简化了数据的展示和处理:

• 使用LayoutManager来确定每一个item的排列方式。

• 为增加和删除项目提供默认的动画效果。

你也可以定义你自己的LayoutManager和添加删除动画，RecyclerView项目结构如下：

• Adapter：使用RecyclerView之前，你需要一个继承自RecyclerView.Adapter的适配器，作用是将数据与每一个item的界面进行绑定。

• LayoutManager：用来确定每一个item如何进行排列摆放，何时展示和隐藏。回收或重用一个View的时候，LayoutManager会向适配器请求新的数据来替换旧的数据，这种机制避免了创建过多的View和频繁的调用findViewById方法（与ListView原理类似）。

  目前SDK中提供了三种自带的LayoutManager:

  • LinearLayoutManager：线性布局，可以实现横向或者纵向的滑动列表（类型ListVIew）

  • GridLayoutManager：表格布局，可以实现类似GridView布局

  • StaggeredGridLayoutManager：瀑布流布局，可以实现瀑布流效果

当然除了上面的三种内部布局之外，我们还可以继承RecyclerView.LayoutManager来实现一个自定义的LayoutManager。

Animations(动画)效果：RecyclerView对于Item的添加和删除是默认开启动画的。我们当然也可以通过RecyclerView.ItemAnimator类定制动画，然后通过RecyclerView.setItemAnimator()方法来进行使用。

RecyclerView相关的类：

RecyclerView.Adapter	托管数据集合，为每个Item创建视图
RecyclerView.ViewHolder	承载Item视图的子视图
RecyclerView.LayoutManager	负责Item视图的布局
RecyclerView.ItemDecoration	为每个Item视图添加子视图，在Demo中被用来绘制Divider
RecyclerView.ItemAnimator	负责添加、删除数据时的动画效果

RecyclerView的基本用法

1、因为RecyclerView是support-v7中的控件，要使用的话我们首先要在build.gradle文件中添加RecyclerView的依赖，添加后我们就能在我们的项目中使用RecyclerView控件了：

dependencies 
    ....
    compile 'com.android.support:recyclerview-v7:23.2.1'

2、在xml布局文件中使用RecyclerView：

<android.support.v7.widget.RecyclerView
    android:id="@+id/rv_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:scrollbars="none"/>

3、对RecyclerView进行获取并设置：

public class MainActivity extends AppCompatActivity 
    private RecyclerView mRecyclerView;
    private MyAdapter mAdapter;
    private ArrayList<String> mDatas = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRecyclerView = (RecyclerView) findViewById(R.id.rv_view);
        //设置LayoutManager类似ListView效果
        mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        //类似横向ListView效果，不反转
        //mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false));
        //类似GridView效果，2列
        //mRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 2));
        //竖向瀑布流效果，2列
        //mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL));
        mRecyclerView.setItemAnimator(new DefaultItemAnimator()); //设置默认动画
        for (int i = 0; i < 20; i++) 
            mDatas.add("卡片：" + i);
        
        mAdapter = new MyAdapter(getActivity(), mDatas);
        mRecyclerView.setAdapter(mAdapter);
        mAdapter.setOnItemClickLitener(new MyAdapter.OnItemClickLitener() 
            @Override
            public void onItemClick(View view, int position) 
                Toast.makeText(getActivity(), "卡片" + position, Toast.LENGTH_SHORT).show();
            
        );
    

Adapter:

public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements View.OnClickListener 

    private LayoutInflater mInflater;
    private ArrayList<String> mDatas = new ArrayList<>();
    private static final int ZERO = 0;
    private static final int ONE = 1;
    private OnItemClickLitener mOnItemClickLitener;

    public MyAdapter(Context context, ArrayList<String> datas) 
        this.mDatas = datas;
        this.mInflater = LayoutInflater.from(context);
    

    //添加数据
    public void addItem(String model, int position) 
        mDatas.add(position, model);
        notifyItemInserted(position);
    

    //更新数据
    public void setData(ArrayList<String> data) 
        this.mDatas= data;
    

    //删除数据
    public void removeItem(String model) 
        int position = mDatas.indexOf(model);
        mDatas.remove(position);
        notifyItemRemoved(position);
    

    //删除数据
    public void removeItem(int position) 
        mDatas.remove(position);
        notifyItemRemoved(position);
    
    @Override
    public void onClick(View view) 
        if (mOnItemClickLitener != null) 
            mOnItemClickLitener.onItemClick(view, (int)view.getTag());
        
    

    public interface OnItemClickLitener 
        void onItemClick(View view, int position);
    

    public void setOnItemClickLitener(OnItemClickLitener mOnItemClickLitener) 
        this.mOnItemClickLitener = mOnItemClickLitener;
    


    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) 
        if (viewType == ONE) 
            return new MyViewHolder(mInflater.inflate(R.layout.item_0, parent, false));
         else 
            return new MyViewHolderTwo(mInflater.inflate(R.layout.item_1, parent, false));
        
    

    @Override
    public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position) 
        if (holder instanceof MyViewHolder) 
            MyViewHolder holder1 = (MyViewHolder) holder;
            holder1.txt.setText(mDatas.get(position));
         else 
            MyViewHolderTwo holder1 = (MyViewHolderTwo) holder;
            holder1.txt.setText(mDatas.get(position));
        
        if (mOnItemClickLitener != null) 
            holder.itemView.setOnClickListener(this);
            holder.itemView.setTag(position);
        
    

    @Override
    public int getItemViewType(int position) 
        if (position % 2 == 0) 
            return ZERO;
         else 
            return ONE;
        
    

    @Override
    public int getItemCount() 
        return mDatas.size();
    

    class MyViewHolder extends RecyclerView.ViewHolder 
        TextView txt;

        public MyViewHolder(View itemView) 
            super(itemView);
            txt = (TextView) itemView.findViewById(R.id.tv_txt);
        
    

    class MyViewHolderTwo extends RecyclerView.ViewHolder 
        TextView txt;

        public MyViewHolderTwo(View itemView) 
            super(itemView);
            txt = (TextView) itemView.findViewById(R.id.tv_txt);
        
    

因为RecyclerView默认没有实现Item的点击事件，所以Item的点击事件需要我们自己来设置，在上面的代码中我们也可以看出来：

private OnItemClickLitener mOnItemClickLitener;

public interface OnItemClickLitener 
    void onItemClick(View view, int position);


public void setOnItemClickLitener(OnItemClickLitener mOnItemClickLitener) 
    this.mOnItemClickLitener = mOnItemClickLitener;


@Override
public void onClick(View view) 
    if (mOnItemClickLitener != null) 
        mOnItemClickLitener.onItemClick(view, (int)view.getTag());
    


@Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position) 
    if (holder instanceof MyViewHolder) 
        MyViewHolder holder1 = (MyViewHolder) holder;
        holder1.txt.setText(mDatas.get(position));
     else 
        MyViewHolderTwo holder1 = (MyViewHolderTwo) holder;
        holder1.txt.setText(mDatas.get(position));
    
    if (mOnItemClickLitener != null) 
        holder.itemView.setOnClickListener(this);
        holder.itemView.setTag(position);
    

mAdapter.setOnItemClickLitener(new MyAdapter.OnItemClickLitener() 
    @Override
    public void onItemClick(View view, int position) 
        Toast.makeText(getActivity(), "卡片" + position, Toast.LENGTH_SHORT).show();
    
);
注意：
在ListView当中，修改数据后可以用Adapter的notifyDataSetChanged()更新界面。而在RecyclerView中还有一些别的方法可以更新数据和界面：
//添加数据
public void addItem(String model, int position) 
    mDatas.add(position, model);
    notifyItemInserted(position);


//添加数据集
public void setData(ArrayList<String> data) 
    this.mDatas= data;
    notifyDataSetChanged();


//删除数据
public void removeItem(String model) 
    int position = mDatas.indexOf(model);
    mDatas.remove(position);
    notifyItemRemoved(position);


//删除数据
public void removeItem(int position) 
    mDatas.remove(position);
    notifyItemRemoved(position);
效果图：
  
以上就是RecyclerView的基本用法。