前言

昨天開始接觸江湖口碑很好的RecyclerView，事實上，我已經被她的強大所征服了！資源回收，資料繫結，佈局顯示，分割線，Item動畫多個模組高度解耦，靈活優雅。其實，RecyclerView在使用上已經是相當簡單了（個人覺得），但仍有很多程式碼是可以加以封裝的。今天受簡書上一篇博文的啟發，作為寫程式碼喜歡優（tou）雅（lan）的人，想到了一種封裝方式，打造萬能介面卡，供大家食用。

正統模式：

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 ; 
}這段程式碼完全可以封裝起來的。
• onCreatedViewHolder()方法作用是繫結item檢視，可以進一步封裝，給子類提供一個getLayoutItemId的抽象方法，這樣就可以簡化成一行程式碼了。
• 因此我們發現，這個adapter的核心程式碼在與onBindViewHolder（）中，作用是將資料跟檢視（ViewHolder）繫結，可以給子類提供一個bindData（）抽象方法。
• 當然了，使用泛型也是極好的，拓廣了adapter的使用範圍。
• 新增點選事件的監聽也可以封裝到萬能adapter中，子類就不用再寫item點選事件處理程式碼了

封裝後的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！

其實，這還沒完呢！重頭戲在ViewHolder上！RecyclerView強制我們使用ViewHolder模式，然而缺不可避免地要寫findViewById程式碼，有沒有辦法不寫這樣的程式碼呢？甚至連ViewHolder都不寫呢？當然可以！

public class RecyclerViewHolder extends RecyclerView.ViewHolder {
    private SparseArray<View> mViews;//集合類，layout裡包含的View,以view的id作為key，value是view物件
    private Context mContext;//上下文物件

    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;
    }
}

該類的核心方法是private T findViewById(int viewId)，核心成員變數是private SparseArray mViews; 不信可以不寫一句ViewHolder程式碼？接下來看看用法。

實踐用法

新增Adapter僅需短短的幾行程式碼：

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) {
                //呼叫holder.getView(),getXXX()方法根據id得到控制元件例項，進行資料繫結即可
                holder.setText(R.id.tv_num,item)
                        .getTextView(R.id.tv_title,item).setText(item);
            }
        };

完整程式碼：

    private void init() {
        recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        mDataList = new ArrayList<>();
        for (int i = 0; i <= 100; i++) {
            mDataList.add(String.valueOf(i));
        }
        //設定item動畫
        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) {
                //呼叫holder.getView(),getXXX()方法根據id得到控制元件例項，進行資料繫結即可
                holder.setText(R.id.tv_num,item)
                        .getTextView(R.id.tv_title,item).setText(item);
            }
        };
        recyclerView.setAdapter(mAdapter);
        //新增item點選事件監聽
        ((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();
            }
        });
        //設定佈局樣式LayoutManager
        recyclerView.setLayoutManager(new LinearLayoutManager(AdapterTestActivity.this, LinearLayoutManager.VERTICAL, false));
// recyclerView.addItemDecoration(new ItemDividerDecoration(MainActivity.this, OrientationHelper.VERTICAL));

    }

如果覺得有什麼不妥之處或建議，敬請指教！ 
完整專案程式碼已上傳至Github。—Github跳轉。