属于RecyclerView的万能适配器Adapter和ViewHolder

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 {

  private List  items;

  public SimplerItemAdapter (@NonNull List dateItems ) {
    this.items = (dateItems != null ? dateItems : new ArrayList());
  }

  @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 extends RecyclerView.Adapter {
    protected final List mData;
    protected final Context mContext;
    protected LayoutInflater mInflater;
    private OnItemClickListener mClickListener;
    private OnItemLongClickListener mLongClickListener;

    public BaseRecyclerAdapter(Context ctx, List list) {
        mData = (list != null) ? list : new ArrayList();
        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 mViews;//集合类，layout里包含的View,以view的id作为key，value是view对象
    private Context mContext;//上下文对象

    public RecyclerViewHolder(Context ctx, View itemView) {
        super(itemView);
        mContext = ctx;
        mViews = new SparseArray();
    }

    private  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(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(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));

    }