手写一个RecycleView的BaseQuickAdapter

1、概述

如上图，整个BaseQuickAdapter的结构还是很简单的，BaseViewHolder负责缓存item View以及常用的操作的封装，而convert抽象方法是我们在BaseQuickAdapter抽象类中暴露给用户的方法，用户只需实现该方法，并在该方法中绑定数据即可，无需了解BaseViewHolder实现的细节。

2、使用

不使用BaseQuickAdapter的代码：

public class MyRecycleViewAdapter extends RecyclerView.Adapter<MyRecycleViewAdapter.MyViewHolder> {

    private List<String> data;
    //支持点击/长按事件
    private OnClick clickLisener;
    private OnLongClick longClickLisener;

    public MyRecycleViewAdapter(List<String> data) {
        this.data = data;
    }

    public void setClickLisener(OnClick clickLisener) {
        this.clickLisener = clickLisener;
    }

    public void setLongClickLisener(OnLongClick longClickLisener) {
        this.longClickLisener = longClickLisener;
    }

    public interface OnClick {
        void myOnClick(View view);
    }

    public interface OnLongClick {
        boolean myOnLongClick(View view);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new MyViewHolder(LayoutInflater.from(MyApplication.context)
                .inflate(R.layout.item_recycleview, parent, false));
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.tv_content.setText(data.get(position));
        holder.ll.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                clickLisener.myOnClick(v);
            }
        });
        holder.ll.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                return longClickLisener.myOnLongClick(v);
            }
        });
    }


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

    class MyViewHolder extends RecyclerView.ViewHolder {

        LinearLayout ll;
        TextView tv_content;

        public MyViewHolder(View itemView) {
            super(itemView);
            tv_content = (TextView) itemView.findViewById(R.id.tv_content);
            ll = (LinearLayout) itemView.findViewById(R.id.ll);
        }
    }

}

使用BaseQuickAdapter的代码：

public class MyRecycleViewAdapter2 extends BaseQuickAdapter<String> {

    public MyRecycleViewAdapter2(List<String> data, int layoutId) {
        super(data, layoutId);
    }

    @Override
    public void convert(BaseViewHolder baseViewHolder, String itemData) {
        baseViewHolder.setText(R.id.tv_content, itemData);
        baseViewHolder.setOnClickLisener(R.id.ll, new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(MyApplication.context, "点击事件", Toast.LENGTH_SHORT).show();
            }
        });
        baseViewHolder.setOnLongClickLisener(R.id.ll, new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                Toast.makeText(MyApplication.context, "长按点击事件", Toast.LENGTH_SHORT).show();
                return false;
            }
        });
    }
}

通过封装BaseQuickAdapter，我们可以发现代码量明显减少了，开发效率必然也就提高了。

3、BaseViewHolder

ViewHolder是RecycleView复用的基本单位，BaseViewHolder将ItemView包含的子View缓存起来以及item常用的操作，包括setText、setImageResource等等封装起来，这样就不用重复书写这些代码，实现整体的复用。

public class BaseViewHolder extends RecyclerView.ViewHolder {

    private View convertView;
    private SparseArray<View> views;//item view缓存

    public BaseViewHolder(View itemView) {
        super(itemView);
        convertView = itemView;
        views = new SparseArray<>();
    }

    //从SparseArray<View> views中查找，有则返回view，无则先缓存再返回view;
    private View getView(int viewId) {
        View view = views.get(viewId);
        if (view == null) {
            view = convertView.findViewById(viewId);
            views.put(viewId, view);
        }
        return view;
    }

    //TextView setText
    public void setText(int viewId, String content) {
        ((TextView) getView(viewId)).setText(content);
    }

    //示例：ImageView 设置背景图
    public void setImageResource(int viewId, int drawableId) {
        View view = getView(viewId);
        if (view instanceof ImageView) {
            ((ImageView) view).setImageResource(drawableId);
        } else
            return;
    }

    //....其他各种set、get方法.....
}

SparseArray<View> views是我们缓存一个item里面子view的集合，这样我们再次使用子view的时候就不需要重复的findViewById了。

3、BaseQuickAdapter

BaseQuickAdapter是一个抽象类，将公用的方法onCreateViewHolder和onBindViewHolder、getItemCount封装起来，这样就不用每次都写这些方法了，有效的减小代码量。同时仅将convert方法暴露出来，只需实现convert方法，并在该方法中绑定数据即可。这里数据的绑定就用到了我们之前封装的BaseViewHolder。

public abstract class BaseQuickAdapter<K> extends RecyclerView.Adapter<BaseViewHolder> {

    private List<K> data;
    private int layoutId;

    //暴露给用户的接口,绑定数据
    public abstract void convert(BaseViewHolder baseViewHolder, K itemData);

    public BaseQuickAdapter(List<K> data, int layoutId) {
        this.data = data;
        this.layoutId = layoutId;
    }

    @Override
    public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new BaseViewHolder(LayoutInflater.from(MyApplication.context).inflate(layoutId, parent, false));
    }

    @Override
    public void onBindViewHolder(BaseViewHolder holder, int position) {
        if (data == null || data.size() == 0)
            return;
        convert(holder, data.get(position));//注意：convert方法必须在onBindViewHolder中调用，将ViewHolder和数据给用户进行绑定
    }

    @Override
    public int getItemCount() {
        return data == null ? 0 : data.size();
    }

}

done!
源码：https://github.com/sparkerandroid/BaseQuickAdapter