Android 轻松定制属于自己的RecyclerViewAdapter

前言

自从RecyclerVIew出来后就尝试着用它，效果真的是比ListView好多了。
但是发现了一个问题，由于RecyclerView的Adapter必须继承自RecyclerView.Adapter，并且指定我们写的ViewHolder为泛型，为了达到万能的效果，我们把需要传入的Java Bean属性直接用一个泛型T指代，我们都在不停的重复写这几个方法①，为何不像之前ListView一样，封装一下呢？

• getItemViewType(int position)
• getItemCount()
• onCreateViewHolder(ViewGroup parent, int viewType)
• onBindViewHolder(RecyclerView.ViewHolder holder, int position)
• 以及定义一个单击事件的接口 OnItemClickListener

那么还有一个问题，为了给用户一个友好的提示，加载更多该怎么做呢。下面带你来封装一下RecyclerView.Adapter，先看看效果图：

使用方法

先看一下封装后的 BaseRecyclerViewAdapter 代码

BaseRecyclerViewAdapter

public abstract class BaseRecyclerViewAdapter<T>
        extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    public static final int TYPE_ITEM = 0;
    public static final int TYPE_FOOTER = 1;

    private int mItemLayoutRes = -1;
    protected Context mContext;
    protected List<T> mList = new ArrayList<>();
    protected OnItemClickListener<T> mOnItemClickListener;
    protected OnReloadClickListener mOnReloadClickListener;

    private FooterViewHolder mFooterViewHolder;

    public BaseRecyclerViewAdapter(Context context, @LayoutRes int itemLayoutRes) {
        this.mContext = context;
        this.mItemLayoutRes = itemLayoutRes;
    }

    public void setOnItemClickListener(OnItemClickListener<T> onItemClickListener) {
        mOnItemClickListener = onItemClickListener;
    }

    public void setOnReloadClickListener(OnReloadClickListener onReloadClickListener) {
        this.mOnReloadClickListener = onReloadClickListener;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == TYPE_FOOTER) {
            View view = getView(parent, R.layout.rv_item_footer);
            return mFooterViewHolder = new FooterViewHolder(view);
        } else {
            View view = getView(parent, mItemLayoutRes);
            final BaseViewHolder baseViewHolder = new BaseViewHolder(view);
            view.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    if (mOnItemClickListener != null) {
                        int position = baseViewHolder.getLayoutPosition();
                        mOnItemClickListener.onItemClick(view, mList.get(position));
                    }
                }
            });
            return baseViewHolder;
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof BaseViewHolder && mList.size() != 0 && mList.size() != position) {
            BaseViewHolder viewHolder = (BaseViewHolder) holder;
            onBindViewHolder(viewHolder, mList.get(position), position);
        } else {
            ViewGroup.LayoutParams layoutParams = holder.itemView.getLayoutParams();
            if (layoutParams != null && layoutParams instanceof
                    StaggeredGridLayoutManager.LayoutParams) {
                StaggeredGridLayoutManager.LayoutParams params =
                        (StaggeredGridLayoutManager.LayoutParams) holder.itemView.getLayoutParams();
                params.setFullSpan(true);
            }
        }
    }

    /**
     * item
     *
     * @param holder   ViewHolder
     * @param data     实体数据
     * @param position 索引
     */
    protected abstract void onBindViewHolder(BaseViewHolder holder, T data, int position);

    protected View getView(ViewGroup parent, int layoutId) {
        return LayoutInflater.from(parent.getContext()).inflate(layoutId, parent, false);
    }

    @Override
    public int getItemCount() {
        int itemCount = mList.size();
        return itemCount == 0 ? 0 : itemCount + 1;
    }

    @Override
    public int getItemViewType(int position) {
        if (position + 1 == getItemCount() && mList.size() > 0) {
            return TYPE_FOOTER;
        }
        return TYPE_ITEM;
    }

    public void setData(List<T> data) {
        mList.clear();
        mList.addAll(data);
        notifyDataSetChanged();
    }

    public void addMoreData(List<T> data) {
        mList.addAll(data);
        notifyDataSetChanged();
    }

    public void deleteData(int position) {
        mList.remove(position);
        notifyItemRemoved(position);
    }

    private class FooterViewHolder extends RecyclerView.ViewHolder {

        ProgressBar progressBar;
        TextView prompt;

        public FooterViewHolder(View itemView) {
            super(itemView);
            progressBar = itemView.findViewById(R.id.pb_loading);
            prompt = itemView.findViewById(R.id.tv_prompt);
        }
    }

    public void setLoading() {
        mFooterViewHolder.prompt.setText("正在加载更多");
        mFooterViewHolder.prompt.setVisibility(View.VISIBLE);
        mFooterViewHolder.progressBar.setVisibility(View.VISIBLE);
    }

    public void setNotMore() {
        mFooterViewHolder.prompt.setText("没有更多了");
        mFooterViewHolder.progressBar.setVisibility(View.GONE);
    }

    public void setNetError() {
        mFooterViewHolder.prompt.setText("加载失败，点击重试");
        mFooterViewHolder.prompt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mOnReloadClickListener != null) {
                    mOnReloadClickListener.onClick();
                }
            }
        });
        mFooterViewHolder.progressBar.setVisibility(View.GONE);
    }
}

创建MainAdapter

public class MainAdapter extends BaseRecyclerViewAdapter<String>{

    public MainAdapter(Context context) {
        super(context, R.layout.rv_item_main);
}

    @Override
    protected void onBindViewHolder(BaseViewHolder holder, String data, int position) {
        holder.setTextView(R.id.item_text_view,data);
    }
}

继承BaseRecyclerViewAdapter后面是泛型实体类，继承后需要实现MainAdapter 构造函数，必须调用super(context, R.layout.rv_item_main)②，实际上是为了初始化父类BaseRecyclerViewAdapter中的一个构造函数

public BaseRecyclerViewAdapter(Context context, @LayoutRes int  itemLayoutRes) {
        this.mContext = context;
        this.mItemLayoutRes = itemLayoutRes;
    }

②：super中的参数
- context 上下文
- item布局id，其实这里也可以在父类中抽象一个 getItemLayoutRes()，返回一个布局id也也可以。

在Activity中使用

public class MainActivity extends AppCompatActivity {

    private static final int COUNT = 15;

    private MainAdapter mAdapter;
    private SwipeRefreshLayout mSwipeRefreshLayout;
    private RecyclerView mRecyclerView;

    private int page = 1;
    private boolean isRefresh;
    private boolean isLoadMore;

    private boolean isFailed = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initView();
        initSwipeRefreshLayout();
        initRecyclerView();
        requestData(COUNT, page);
    }

    private void initView() {
        mSwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipe_refresh_layout);
        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    }

    private void initSwipeRefreshLayout() {
        mSwipeRefreshLayout.setRefreshing(true);
        mSwipeRefreshLayout.setColorSchemeColors(getResources()
                .getIntArray(R.array.swipeRefreshLayoutColor));
        mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                page = 1;
                isRefresh = true;
                requestData(COUNT, page);
            }
        });
    }

    private void initRecyclerView() {
        mAdapter = new MainAdapter(this);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecyclerView.setAdapter(mAdapter);
        // 单击事件
        mAdapter.setOnItemClickListener(new OnItemClickListener<String>() {
            @Override
            public void onItemClick(View view, String data) {
                Toast.makeText(MainActivity.this, "点击了" + data, Toast.LENGTH_SHORT).show();
            }
        });
        // 请求异常重试监听
        mAdapter.setOnReloadClickListener(new OnReloadClickListener() {
            @Override
            public void onClick() {
                mAdapter.setLoading();
                requestData(COUNT, page);
            }
        });
        // 滑到底部监听事件
        mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                LinearLayoutManager lm = (LinearLayoutManager) recyclerView.getLayoutManager();
                int totalItemCount = recyclerView.getAdapter().getItemCount();
                int lastVisibleItemPosition = lm.findLastVisibleItemPosition();
                int visibleItemCount = recyclerView.getChildCount();
                if (!isRefresh && !isLoadMore && newState == RecyclerView.SCROLL_STATE_IDLE &&
                        lastVisibleItemPosition == totalItemCount - 1 && visibleItemCount > 0) {
                    isLoadMore = true;
                    isRefresh = false;
                    mAdapter.setLoading();
                    requestData(COUNT, page);
                }
            }
        });
    }

    /**
     * 模拟网络请求数据
     *
     * @param count 请求数量
     * @param page  请求页码
     */
    private void requestData(int count, final int page) {
        final List<String> list = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            list.add("item " + i);
        }
        // 延迟执行
        new Handler().postDelayed(new Runnable() {

            @Override
            public void run() {
                // 模拟请求失败时情况
                if (isFailed && page == 3) {
                    onFailed("无网络链接");
                    isFailed = false;
                    return;
                }else if (page == 4){
                    list.clear();
                }
                isFailed = true;
                resultData(list);
            }
        }, 1500);
    }

    /**
     * 模拟请求数据成功后返回的数据
     *
     * @param list 数据源
     */
    private void resultData(List<String> list) {
        closeRefreshing();
        if (isRefresh) {
            if (list != null && list.size() > 0) {
                mAdapter.setData(list);
                page++;
            } else {
                Toast.makeText(this, "暂无数据", Toast.LENGTH_SHORT).show();
            }
        } else {
            if (list != null && list.size() > 0) {
                Log.d("wz", "加载更多");
                mAdapter.addMoreData(list);
                page++;
            } else {
                mAdapter.setNotMore();
            }
        }
        isRefresh = false;
        isLoadMore = false;
    }

    /**
     * 模拟数据请求失败结果
     *
     * @param errorMsg msg
     */
    public void onFailed(String errorMsg) {
        closeRefreshing();
        if (mAdapter.getItemCount() == 0) {
            Toast.makeText(this, "加载出错：" + errorMsg, Toast.LENGTH_SHORT).show();
        } else {
            mAdapter.setNetError();
        }
    }

    /**
     * 关闭 SwipeRefreshLayout 下拉动画
     */
    private void closeRefreshing() {
        if (mSwipeRefreshLayout.isRefreshing()) {
            mSwipeRefreshLayout.setRefreshing(false);
        }
    }

}

这里我是模拟测试，真正使用没那么复杂，按照自己的想法去做就行。

BaseViewHolder

RecyclerView要求必须使用ViewHolder模式，一般我们在使用过程中，都需要去建立一个新的ViewHolder然后作为泛型传入Adapter。那么想要建立通用的Adapter，必须有个通用的ViewHolder。

首先我们确定下ViewHolder的主要的作用，实际上是通过成员变量存储对应的convertView中需要操作的字View，避免每次findViewById，从而提升运行的效率。

那么既然是通用的View，那么对于不同的ItemType肯定没有办法确定创建哪些成员变量View，取而代之的只能是个集合来存储了。
代码如下：

public class BaseViewHolder extends RecyclerView.ViewHolder {

    private SparseArray<View> mViews;
    private View mConvertView;

    public BaseViewHolder(View itemView) {
        super(itemView);
        mConvertView = itemView;
        mViews = new SparseArray<View>();
    }

    public static BaseViewHolder get(ViewGroup parent, int layoutId) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(layoutId, parent, false);
        return get(itemView);
    }

    public static BaseViewHolder get(View view){
        return new BaseViewHolder(view);
    }

    /**
     * 通过viewId获取控件
     *
     * @param viewId
     * @return
     */
    public <T extends View> T getView(int viewId) {
        View view = mViews.get(viewId);
        if (view == null) {
            view = mConvertView.findViewById(viewId);
            mViews.put(viewId, view);
        }
        return (T) view;
    }

    public BaseViewHolder setTextView(int viewId, String text) {
        TextView view = getView(viewId);
        view.setText(text);
        return this;
    }
}

代码很简单，我们的ViewHolder继承自RecyclerView.ViewHolder，内部通过SparseArray来缓存我们itemView内部的子View，从而得到一个通用的ViewHolder。每次需要创建ViewHolder只需要传入我们的view即可。

itemView单击事件

public interface OnItemClickListener<T> {

    /**
     * 单击事件
     * @param view itemView
     * @param data 实体类数据
     */
    void onItemClick(View view, T data);

}

这里定义了一个范型接口，对应 BaseRecyclerViewAdapter 中的范型T类。

底部重试点击事件

public interface OnReloadClickListener {

    /**
     * 重试点击事件
     */
    void onClick();
}

只有在底部加载失败的情况下，点击item触发该onClick()

结尾

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