RecyclerView（笔记）

写在前面

ListView早些时候还没用熟，后来就出了个RecyclerView，怀着好奇心和贪图所谓的“方便”，就对ListView嗤之以鼻，也不太知道它的使用方法了。现在也懒得回去重新看，就直接对RecyclerView下手了。

记录下自己对这个东西的一个入门学习。

首先如果是在AndroidStudio里的话，使用RecycleView直接Gradle即可。在eclipse里的话就需要多费些心思，要注意v7包与RecyclerView包的版本一致的问题。具体配置就不记录了。

从最基本用起：

public class MainActivity extends Activity {private RecyclerView rl_main;private MainViewAdapter mainViewAdapter;private List<User> dataList;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);rl_main = (RecyclerView) findViewById(R.id.rl_main);dataList = new ArrayList<>();for (int i = 0; i < 30; i++) {dataList.add(new User("name" + i + "  ", R.drawable.ic_launcher));}mainViewAdapter = new MainViewAdapter(this, dataList, R.layout.item);rl_main.setAdapter(mainViewAdapter);rl_main.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));}}

适配器和ViewHolder：

public class MainViewAdapter extends RecyclerView.Adapter<MyViewHolder> {private Context mContext;private List<User> mList;private int itemId;public MainViewAdapter(Context context, List<User> dataList, int itemId) {// TODO Auto-generated constructor stubmContext = context;mList = dataList;this.itemId = itemId;}@Overridepublic int getItemCount() {// TODO Auto-generated method stubreturn mList.size();}@Overridepublic void onBindViewHolder(MyViewHolder viewHolder, int position) {// TODO Auto-generated method stubviewHolder.tv_item.setText(mList.get(position).getName());viewHolder.iv_item.setBackgroundResource(mList.get(position).getImg());}@Overridepublic MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {// TODO Auto-generated method stubView view = LayoutInflater.from(mContext).inflate(itemId, parent, false);MyViewHolder myViewHolder = new MyViewHolder(view);return myViewHolder;}}class MyViewHolder extends ViewHolder {TextView tv_item;ImageView iv_item;public MyViewHolder(View itemView) {super(itemView);// TODO Auto-generated constructor stubtv_item = (TextView) itemView.findViewById(R.id.tv_item);iv_item = (ImageView) itemView.findViewById(R.id.iv_item);}}

图：

A ViewHolder describes an item view and metadata about its place within the RecyclerView.
RecyclerView.Adapter implementations should subclass ViewHolder and add fields for caching potentially expensive findViewById(int) results.

大致说ViewHolder是用于描述我们的item布局和在里面的元数据，或者说就是对item里面的控件进行 findViewById(int) 的绑定。

在实现Adapter的时候，需要重写三个方法：

onCreateViewHolder(ViewGroup parent, int viewType)

getItemCount()

onBindViewHolder(MyViewHolder viewHolder, int position)

onCreateViewHolder(ViewGroup parent, int viewType) ：

This method calls onCreateViewHolder(ViewGroup, int) to create a new RecyclerView.ViewHolder and initializes some private fields to be used by RecyclerView.

在这里创建我们的ViewHolder并初始化一些在RecyclerView里会被使用的私有的东西，像给ViewHolder指定item的布局，为每个item添加点击事件等。

getItemCount() ：

Returns the total number of items in the data set hold by the adapter.

一般我们都是返回对象的size。

onBindViewHolder(MyViewHolder viewHolder, int position)：

Called by RecyclerView to display the data at the specified position. This method should update the contents of the itemView to reflect the item at the given position.

在这里我们就要对item里的控件进行数据的设置显示了。

加些东西：

多Item布局：

实现让第一个item和最后一个item显示图片，其余的按照dataList的内容显示文字。

定义两个ViewHolder，并对其作出相关判断。

public class MultipleItemAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {// 用枚举类型来标记item的类型public enum HOLDER_TYPE {ITEM_IMAGE, ITEM_TEXT}private Context mContext;private List<String> mList;public MultipleItemAdapter(Context context, List<String> dataList) {mContext = context;mList = dataList;}@Overridepublic int getItemCount() {// TODO Auto-generated method stubreturn mList.size();}@Overridepublic void onBindViewHolder(ViewHolder holder, int position) {// TODO Auto-generated method stubif (holder instanceof TextViewHolder) {((TextViewHolder) holder).textview.setText(mList.get(position));}}@Overridepublic ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {// TODO Auto-generated method stubView itemTextView = LayoutInflater.from(mContext).inflate(R.layout.item_text, parent, false);View itemImageView = LayoutInflater.from(mContext).inflate(R.layout.item_image, parent, false);if (viewType == HOLDER_TYPE.ITEM_TEXT.ordinal()) {TextViewHolder textViewHolder = new TextViewHolder(itemTextView);return textViewHolder;} else {ImageViewHolder imageViewHolder = new ImageViewHolder(itemImageView);return imageViewHolder;}}@Overridepublic int getItemViewType(int position) {// TODO Auto-generated method stubif (position != 0 && position != mList.size() - 1) {return HOLDER_TYPE.ITEM_TEXT.ordinal();} else {return HOLDER_TYPE.ITEM_IMAGE.ordinal();}}}class TextViewHolder extends RecyclerView.ViewHolder {TextView textview;public TextViewHolder(View itemView) {super(itemView);// TODO Auto-generated constructor stubtextview = (TextView) itemView.findViewById(R.id.tv_item);}}class ImageViewHolder extends RecyclerView.ViewHolder {ImageView imageView;public ImageViewHolder(View itemView) {super(itemView);// TODO Auto-generated constructor stubimageView = (ImageView) itemView.findViewById(R.id.iv_item);}}

这里主要多了getItemViewType(int position)这个方法。

Return the view type of the item at position for the purposes of view recycling.

根据位置来获取每个item的类型，这个类型也就是onCreateViewHolder(ViewGroup parent, int viewType) 里的viewType

参考与扩展：

RecyclerView使用详解（二）

RecyclerView.Adapter（需科学上网）