Android RecyclerView

RecyclerView是一个强大的滚动控件,可以说是一个加强版的ListView,不仅可以实现ListView的效果,还优化了ListView的不足之处,
1.RecyclerView的基本用法
要想使用RecyclerView这个控件,首先要在项目的build.gradle中添加相应的依赖库才行
打开app/buile.gradle 文件,在dependencies闭包中添加如下内容:

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

添加完之后记得要点击一下 Sync Now 来进行同步,
修改Activity_main.xml代码

<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>

Fruit类,name表示水果的名称,imageId表示水果对应的图片资源id

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;    }}

fruit_item.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="wrap_content">    <ImageView        android:id="@+id/fruit_image"        android:layout_width="wrap_content"        android:layout_height="wrap_content"/>    <TextView        android:id="@+id/fruit_name"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_vertical"        android:layout_marginLeft="10dp"/></LinearLayout>

然后为RecyclerView定义一个适配器,这个适配器继承自RecyclerView.Adapter,并将泛型指定为FruitAdapter.ViewHolder,其中ViewHolder是FruitAdapter中定义的一个内部类,代码如下:

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder>{    private List<Fruit> mFruitList;    static class ViewHolder extends RecyclerView.ViewHolder{        ImageView fruitImage;        TextView fruitName;        public ViewHolder(View view){            super(view);            fruitImage = (ImageView)view.findViewById(R.id.fruit_image);            fruitName = (TextView)view.findViewById(R.id.fruit_name);        }    }    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);        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 getItemContent(){        return mFruitList.size();     }}

MainActivity.java

public class MainActivity extends AppCompatActivity{    private List<Fruit> fruitList = new ArrayList<>();    @Override    protected void onCreate(Bundle savedInstanceState){        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initFruits();//初始化水果数据        RecyclerView recyclerView = (RecyclerView)findViewById(R.id.recycler_view);        LinearLayoutManager layoutManager = new LinearLayoutManager(this);        recyclerView.setLayoutManager(layoutManager);        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);            Fruit banana = new Fruit("Banana",R.drawable.banana_pic);            fruitList.add(banana);            Fruit orange = new Fruit("Orange",R.drawable.orange_pic);            fruitList.add(orange);            Fruit watermelon = new Fruit("Watermelon",R.drawable.watermelon_pic);            fruitList.add(watermelon);            Fruit pear = new Fruit("Pear",R.drawable.pear_pic);            fruitList.add(pear);            Fruit grape = new Fruit("Grape",R.drawable.grape_pic);            fruitList.add(grape);            Fruit pineapple = new Fruit("Pineapple",R.drawable.pineapple_pic);            fruitList.add(pineapple);            Fruit strawberry = new Fruit("Strawberry",R.drawable.strawberry_pic);            fruitList.add(strawberry);            Fruit cherry = new Fruit("Cherry",R.drawable.cherry_pic);            fruitList.add(cherry);            Fruit mango = new Fruit("Mango",R.drawable.mango_pic);            fruitList.add(mango);        }    }}

2.实现横向滚动和瀑布流布局
首先要对fruit_item.xml布局进行修改,因为目前这个布局里面的元素是水平排列的,适用于纵向滚动的场景,而如果我们要实现横向滚动的话,应该把fruit_item中的元素改为垂直排列,代码如下
我们将LinearLayout改为垂直方向排列,并把宽度设为100dp,这里将宽度指定为固定值是因为每种水果的文字长度不一样,如果使用wrap_content的话,RecyclerView子项就会有长有短,非常不美观,如果使用match_parent的话,长度就过长,一个子项占满整个屏幕.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="100dp"    android:layout_height="wrap_content">    <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="center_horizontal"        android:layout_marginTop="10dp"/></LinearLayout>

修改MainActivity中的代码

public class MainActivity extends AppCompatActivity{    private List<Fruit> fruitList = new ArrayList<>();    @Override    protected void onCreate(Bundle savedInstanceState){        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initFruits();//初始化水果数据        RecyclerView recyclerView = (RecyclerView)findViewById(R.id.recycler_view);        LinearLayoutManager layoutManager = new LinearLayoutManager(this);        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);        recyclerView.setLayoutManager(layoutManager);        FruitAdapter adapter = new FruitAdapter(fruitList);        recyclerView.setAdapter(adapter);    }    ...}

调用LinearLayoutManager的setOrientation()方法来设置布局的排列方向,默认是纵向排列的,我们传入的LinearLayoutManager.HORIZONTAL表示让布局横行排列.这样就可以横向滚动了

瀑布流布局的实现
首先要对fruit_item.xml布局进行修改
首先将LinearLayout的宽度由100dp改为match_parent,因为瀑布流布局的宽度应该是根据布局的列数来自动适配的,而不是一个固定值,另外我们使用了layout_margin属性来让子项之间互留一点间距,这样就不会所有的子项都紧贴在一起,还有就是将TextView的对齐方式改为居左对齐.

<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>

修改MainActivity中的代码
在onCreate()方法中,我们创建了一个StaggeredGridLayoutManager的实例,StaggeredGridLayoutManager的构造函数接收两个参数,第一个参数用于指定布局的列数,传入3会表示把布局分为3列,第二个参数用于指定布局的排列方向,传入StaggeredGridLayoutManager.VERITCAL表示会让布局纵向排列,最后把创建好的实例设置到RecyclerView中就可以了.
getRandomLengthName()方法,这个方法使用了Random对象来创造一个1到20之间的随机数,然后将参数中传入的字符串重复随机遍,在initFruits()方法中,每个水果的名字都改为调用getRandomLengthName()这个方法来生成,这样就能保证各水果名字的长短差距都比较大,子项的高度也就各不相同了.

public class MainActivity extends AppCompatActivity{    private List<Fruit> fruitList = new ArrayList<>();    @Override    protected void onCreate(Bundle savedInstanceState){        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initFruits();//初始化水果数据        RecyclerView recyclerView = (RecyclerView)findViewById(R.id.recycler_view);        StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);        recyclerView.setLayoutManager(layoutManager);        FruitAdapter adapter = new FruitAdapter(fruitList);        recyclerView.setAdapter(adapter);    }    private void initFruits(){        for(int i = 0;i < 2;i++){            Fruit apple = new Fruit(getRandomLengthName("Apple"),R.drawable.apple_pic);            fruitList.add(apple);            Fruit banana = new Fruit(getRandomLengthName("Banana"),R.drawable.banana_pic);            fruitList.add(banana);            Fruit orange = new Fruit(getRandomLengthName("Orange"),R.drawable.orange_pic);            fruitList.add(orange);            Fruit watermelon = new Fruit(getRandomLengthName("Watermelon"),R.drawable.watermelon_pic);            fruitList.add(watermelon);            Fruit pear = new Fruit(getRandomLengthName("Pear"),R.drawable.pear_pic);            fruitList.add(pear);            Fruit grape = new Fruit(getRandomLengthName("Grape"),R.drawable.grape_pic);            fruitList.add(grape);            Fruit pineapple = new Fruit(getRandomLengthName("Pineapple"),R.drawable.pineapple_pic);            fruitList.add(pineapple);            Fruit strawberry = new Fruit(getRandomLengthName("Strawberry"),R.drawable.strawberry_pic);            fruitList.add(strawberry);            Fruit cherry = new Fruit(getRandomLengthName("Cherry"),R.drawable.cherry_pic);            fruitList.add(cherry);            Fruit mango = new Fruit(getRandomLengthName("Mango"),R.drawable.mango_pic);            fruitList.add(mango);        }    }    private String getRandomLengthName(String name){        Random random = new Random();        int length = random.nextInt(20) + 1;        StringBuilder builder = new StringBuilder();        for (int i = 0;i < length;i++) {            builder.append(name);        }        return builder.toString();    }}

3.RecyclerView的点击事件
不同于ListView的是,RecyclerView并没有提供类似于setOnItemClickListener()这样的注册监听器方法,而是需要我们自己给子项具体的View去注册点击事件,相对于ListView要复杂一点

修改FruitAdapter的代码:
我们先修改了ViewHolder,在ViewHolder中添加了fruitView变量来保存子项最外层布局的实例,然后在onCreateViewHolder()方法中注册点击事件就可以了,这里分别为最外层的布局和ImageView都注册了点击事件,RecyclerView的强大之处就在这里,它可以轻松实现子项中任意控件或布局的点击事件,我们在两个点击事件中先获取了用户点击的position,然后通过position拿到相应的Fruit实例,再使用Toast分别弹出两种不同的内容以示区别.

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder>{    private List<Fruit> mFruitList;    static 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);        }    }    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);        fianl 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;    }    ...}