偷懒新姿势，打造属于RecyclerView的万能适配器Adapter和ViewHolder

时间:2022-04-26
本文章向大家介绍偷懒新姿势，打造属于RecyclerView的万能适配器Adapter和ViewHolder，主要内容包括前言、正统模式：、封装后的Adapter、Super ViewHolder、实践用法、基本概念、基础应用、原理机制和需要注意的事项等，并结合实例形式分析了其使用技巧，希望通过本文能帮助到大家理解应用这部分内容。

前言

昨天开始接触江湖口碑很好的RecyclerView，事实上，我已经被她的强大所征服了！资源回收，数据绑定，布局显示，分割线，Item动画多个模块高度解耦，灵活优雅。其实，RecyclerView在使用上已经是相当简单了（个人觉得），但仍有很多代码是可以加以封装的。今天受简书上一篇博文的启发，作为写代码喜欢优（tou）雅（lan）的人，想到了一种封装方式，打造万能适配器，供大家食用。

正统模式：

public class SimplerItemAdapter extends RecyclerView.Adapter<SimplerItemAdapter.SimpleItemViewHolder > {    
    private List <String> items;  
    public SimplerItemAdapter (@NonNull List<String> dateItems ) {    this.items = (dateItems != null ? dateItems : new ArrayList<String>());   
    }    
    
    @Override 
    public SimpleItemViewHolder onCreateViewHolder (ViewGroup viewGroup, int viewType) {     
    View itemView = LayoutInflater.from( viewGroup.getContext ()).inflate(R.layout .item, viewGroup, false );    
    return new SimpleItemViewHolder(itemView);   
    }   
    
     @Override 
     public void onBindViewHolder (SimpleItemViewHolder viewHolder, int position) {     
     viewHolder.textView .setText(items.get (position));   
     }    
     
     @Override 
     public int getItemCount () {    
     return (this.items != null) ? this .items. size() : 0 ;   
     }  
     
     protected final static class SimpleItemViewHolder extends RecyclerView.ViewHolder {     
     protected TextView textView ;    
     public SimpleItemViewHolder (View itemView) {      
         super(itemView);      
         this.textView = (TextView) itemView.findViewById (R. id.text);     }   
     }     
}
  • 首先， @Override public int getItemCount () { return (this.items != null) ? this .items. size() : 0 ; }这段代码完全可以封装起来的。
  • onCreatedViewHolder()方法作用是绑定item视图，可以进一步封装，给子类提供一个getLayoutItemId的抽象方法，这样就可以简化成一行代码了。
  • 因此我们发现，这个adapter的核心代码在与onBindViewHolder（）中，作用是将数据跟视图（ViewHolder）绑定，可以给子类提供一个bindData（）抽象方法。
  • 当然了，使用泛型也是极好的，拓广了adapter的使用范围。
  • 添加点击事件的监听也可以封装到万能adapter中，子类就不用再写item点击事件处理代码了

封装后的Adapter

public abstract class BaseRecyclerAdapter<T> extends RecyclerView.Adapter<RecyclerViewHolder> {    
    protected final List<T> mData;    
    protected final Context mContext;    
    protected LayoutInflater mInflater;    
    private OnItemClickListener mClickListener;    
    private OnItemLongClickListener mLongClickListener;    
    public BaseRecyclerAdapter(Context ctx, List<T> list) {               mData = (list != null) ? list : new ArrayList<T>();               mContext = ctx;         

        mInflater = LayoutInflater.from(ctx);     

    }      

    @Override    
    public RecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {         

    final RecyclerViewHolder holder = new RecyclerViewHolder(mContext,                 

    mInflater.inflate(getItemLayoutId(viewType), parent, false));     if (mClickListener != null) {             

    holder.itemView.setOnClickListener(new View.OnClickListener() 

        @Override                

        public void onClick(View v) {                     

        mClickListener.onItemClick(holder.itemView, holder.getLayoutPosition());                 

        }             });         

    }        

    if (mLongClickListener != null) {             

    holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {                 

    @Override                

    public boolean onLongClick(View v) {                     

    mLongClickListener.onItemLongClick(holder.itemView, holder.getLayoutPosition());                    

    return true;                 

        }             });         

    }        

    return holder;     
}      
    @Override    
    public void onBindViewHolder(RecyclerViewHolder holder, int position) {         

    bindData(holder, position, mData.get(position));     

    }      

    @Override    

    public int getItemCount() {        

    return mData.size();     

    }    

    public void add(int pos, T item) {         

    mData.add(pos, item);         

    notifyItemInserted(pos);     

    }    

    public void delete(int pos) {         

    mData.remove(pos);         

    notifyItemRemoved(pos);     

    }    

    public void setOnItemClickListener(OnItemClickListener listener) {         

    mClickListener = listener;     

    }    

    public void setOnItemLongClickListener(OnItemLongClickListener listener) {         

    mLongClickListener = listener;     

    }    

    abstract public int getItemLayoutId(int viewType);    

    abstract public void bindData(RecyclerViewHolder holder, int position, T item);    

    public interface OnItemClickListener {        

        public void onItemClick(View itemView, int pos);     

    }    

    public interface OnItemLongClickListener {        

        public void onItemLongClick(View itemView, int pos);     

    } 
}

Super ViewHolder

其实，这还没完呢！重头戏在ViewHolder上！RecyclerView强制我们使用ViewHolder模式，然而缺不可避免地要写findViewById代码，有没有办法不写这样的代码呢？甚至连ViewHolder都不写呢？当然可以！

public class RecyclerViewHolder extends RecyclerView.ViewHolder {     private SparseArray<View> mViews;     
    private Context mContext;      

    public RecyclerViewHolder(Context ctx, View itemView) {               super(itemView);         
        mContext = ctx;         
        mViews = new SparseArray<View>();     
    }    
    
    private <T extends View> T findViewById(int viewId) {                 View view = mViews.get(viewId);        
        if (view == null) {             
        view = itemView.findViewById(viewId);             
        mViews.put(viewId, view);         
        }        
        return (T) view;     
    }    
    
    public View getView(int viewId) {        
        return findViewById(viewId);     
    }    
    
    public TextView getTextView(int viewId) {        
        return (TextView) getView(viewId);     
    }    
    
    public Button getButton(int viewId) {        
        return (Button) getView(viewId);     
    }    
    
    public ImageView getImageView(int viewId) {        
        return (ImageView) getView(viewId);     
    }    
    
    public ImageButton getImageButton(int viewId) {        
        return (ImageButton) getView(viewId);     
    }    
    
    public EditText getEditText(int viewId) {        
        return (EditText) getView(viewId);     
    }    
    
    public RecyclerViewHolder setText(int viewId, String value) {         TextView view = findViewById(viewId);         
        view.setText(value);        
        return this;     
    }    
    
    public RecyclerViewHolder setBackground(int viewId, int resId) {         
        View view = findViewById(viewId);         
        view.setBackgroundResource(resId);        
        return this;     
    }    
    
    public RecyclerViewHolder setClickListener(int viewId, View.OnClickListener listener) {         
        View view = findViewById(viewId);         
        view.setOnClickListener(listener);        
        return this;     } 
    }

该类的核心方法是private T findViewById(int viewId)，核心成员变量是private SparseArray mViews; 不信可以不写一句ViewHolder代码？接下来看看用法。

实践用法

添加Adapter仅需短短的几行代码：

Adapter = new BaseRecyclerAdapter<String>(this,mDataList) {            @Override             
    public int getItemLayoutId(int viewType) {                
        return R.layout.item;             
    }            
    
    @Override             
    public void bindData(RecyclerViewHolder holder, int position,String item) {
     //调用holder.getView(),getXXX()方法根据id得到控件实例，进行数据绑定即可                          
        holder.setText(R.id.tv_num,item).getTextView(R.id.tv_title,item).setText(item);             
    }         
};

完整代码：

private void init() {         
    recyclerView = (RecyclerView) findViewById(R.id.recyclerView);    mDataList = new ArrayList<>();        
    for (int i = 0; i <= 100; i++) {             
        mDataList.add(String.valueOf(i));         
    }       
     //设置item动画
    recyclerView.setItemAnimator(new DefaultItemAnimator());          mAdapter = new BaseRecyclerAdapter<String>(this,mDataList) {            
    @Override             
    public int getItemLayoutId(int viewType) {                
     
        return R.layout.item;             
     
    }            
    
     @Override             
     public void bindData(RecyclerViewHolder holder, int position,String item) {   
     
       //调用holder.getView(),getXXX()方法根据id得到控件实例，进行数据绑定即可             
         holder.setText(R.id.tv_num,item).getTextView(R.id.tv_title,item).setText(item);             
     }    
          
     };   
           
     recyclerView.setAdapter(mAdapter);     
       
     //添加item点击事件监听 
    ((BaseRecyclerAdapter)mAdapter).setOnItemClickListener(new BaseRecyclerAdapter.OnItemClickListener() {  
               
     @Override             
     public void onItemClick(View itemView, int pos) {                     Toast.makeText(AdapterTestActivity.this, "click " + pos, Toast.LENGTH_SHORT).show();            
     
      }         
      });         
      
      ((BaseRecyclerAdapter)mAdapter).setOnItemLongClickListener(new BaseRecyclerAdapter.OnItemLongClickListener() {  
                
      @Override             
      public void onItemLongClick(View itemView, int pos) {                 Toast.makeText(AdapterTestActivity.this, "long click " + pos, Toast.LENGTH_SHORT).show();             
      }   
            
      });
              
        //设置布局样式LayoutManager
      recyclerView.setLayoutManager(new LinearLayoutManager(AdapterTestActivity.this, LinearLayoutManager.VERTICAL, false));
      //        recyclerView.addItemDecoration(new ItemDividerDecoration(MainActivity.this, OrientationHelper.VERTICAL));
      }

如果觉得有什么不妥之处或建议，敬请指教！ 完整项目代码已上传至Github(https://github.com/TellH/RecyclerViewDemo)。

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