【Android】recyclerView-1-简单使用

首先来看一个简单的用法。

1、在build.gradle（app）中的dependencies闭包中添加远程依赖

dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    testCompile 'junit:junit:4.12'    compile 'com.android.support:appcompat-v7:24.2.1'    compile 'com.android.support:recyclerview-v7:24.2.1'}

2、在大布局里添加RecyclerView控件

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent">    <android.support.v7.widget.RecyclerView        android:id="@+id/recycler_view"        android:layout_width="match_parent"        android:layout_height="match_parent" /></LinearLayout>

3、新建RecyclerView的子布局fruit_item.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:layout_margin="5dp" >    <ImageView        android:id="@+id/fruit_image"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_horizontal" />    <TextView        android:id="@+id/fruit_name"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="left"        android:layout_marginTop="10dp" /></LinearLayout>

4、新建一个ViewHolder类，继承RecyclerView.Holder

public class ViewHolder extends RecyclerView.ViewHolder {    View fruitView;    ImageView fruitImage;    TextView fruitName;    public ViewHolder(View view) {        super(view);        fruitView = view;        fruitImage = (ImageView) view.findViewById(R.id.fruit_image);        fruitName = (TextView) view.findViewById(R.id.fruit_name);    }}

5、新建一个Fruit类

public class Fruit {    private String name;    private int imageId;    public Fruit(String name, int imageId) {        this.name = name;        this.imageId = imageId;    }    public String getName() {        return name;    }    public int getImageId() {        return imageId;    }}

6、新建一个FruitAdapter类，继承自RecyclerView.Adapter类。

public class FruitAdapter extends RecyclerView.Adapter<ViewHolder>{    private List<Fruit> mFruitList;    public FruitAdapter(List<Fruit> fruitList) {        mFruitList = fruitList;    }    @Override    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);        final ViewHolder holder = new ViewHolder(view);        holder.fruitView.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                int position = holder.getAdapterPosition();                Fruit fruit = mFruitList.get(position);                Toast.makeText(v.getContext(), "you clicked view " + fruit.getName(), Toast.LENGTH_SHORT).show();            }        });        holder.fruitImage.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                int position = holder.getAdapterPosition();                Fruit fruit = mFruitList.get(position);                Toast.makeText(v.getContext(), "you clicked image " + fruit.getName(), Toast.LENGTH_SHORT).show();            }        });        return holder;    }    @Override    public void onBindViewHolder(ViewHolder holder, int position) {        Fruit fruit = mFruitList.get(position);        holder.fruitImage.setImageResource(fruit.getImageId());        holder.fruitName.setText(fruit.getName());    }    @Override    public int getItemCount() {        return mFruitList.size();    }}

7、在Activity里初始化配置

public class MainActivity extends AppCompatActivity {    private List<Fruit> fruitList = new ArrayList<Fruit>();    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);        StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.HORIZONTAL);        recyclerView.setLayoutManager(layoutManager);        initFruits();        FruitAdapter adapter = new FruitAdapter(fruitList);        recyclerView.setAdapter(adapter);    }    private void initFruits() {        for (int i = 0; i < 2; i++) {            Fruit apple = new Fruit("apple", R.drawable.apple_pic);            fruitList.add(apple);        }    }}

解析：

我之前觉得Recyclerview很难用，因为我觉得它很繁琐，很乱，我也不明白它的机制，只是觉得很神奇，只要这么配置，它就自己能生成一个可滑动的列表组件。后来我终于明白它的原理（没看过源码，自以为的原理），才发现原来是这样。

它的核心是一个adapter，adapter的主要任务，遍历一个集合，遍历过程中将集合元素的属性和子项布局绑定。

我们拿上面的代码来分析：

public class FruitAdapter extends RecyclerView.Adapter<ViewHolder>{    private List<Fruit> mFruitList;    public FruitAdapter(List<Fruit> fruitList) {        mFruitList = fruitList;    }    @Override    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);        final ViewHolder holder = new ViewHolder(view);        return holder;    }    @Override    public void onBindViewHolder(ViewHolder holder, int position) {        Fruit fruit = mFruitList.get(position);        holder.fruitImage.setImageResource(fruit.getImageId());        holder.fruitName.setText(fruit.getName());    }    @Override    public int getItemCount() {        return mFruitList.size();    }}

先看它的构造方法：获得一个集合对象，这个对象的元素里所包含的属性，应该就是我们想在列表项里，单个模块想展示的内容。

然后看onCreateViewHolder()方法：ViewHolder这个类，其实是一个引用暂存类，它的引用变量直接指向了子项布局的组件的对象。所以这个方法就是子项布局的引用都存到holder这个引用指向的对象里。

再看onBindViewHolder()方法：这个方法应该在遍历集合元素的时候调用，遍历时会将holder指向的布局组件进行资源设置，其实应该是根据position生成了一个子项布局的拷贝，遍历时都设置一番，我们最终应该只看到一个组件，并且属性为最后一次的设置，由此可知是在设置拷贝的对象的属性。

最后看getItemCount()方法：这个应该就是遍历的长度。

以上分析，纯属猜测和脑补，有什么不对的，我也没办法啊。