更强大的滚动控件——RecyclerView

ListView只能实现数据纵向滚动的效果，如果我们想实现横向滚动的话，ListView是做不到的。

Android提供了一个更强大的滚动控件——RecyclerView。它可以说是一个增强版的ListView，不仅可以轻松实现和ListView同样的效果，还优化了ListView中存在的各种不足之处。

打开app/build.gradle文件，在dependencies闭包中添加如下内容：

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:26.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
    implementation 'com.android.support:design:26.1.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    compile 'com.android.support:recyclerview-v7:26.1.0'
}

为RecyclerView准备一个适配器，新建FruitAdapter类，让这个适配器继承自RecyclerView.Adapter，并将泛型指定为FruitAdapter.ViewHolder。其中，ViewHolder是我们在FruitAdapter中定义的一个内部类

public class FruitAdapter extends RecyclerView.Adapter {

    private List 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(ListfruitList){
        mFruitList=fruitList;
    }
    @Override
    public FruitAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,null,false);//这里设置parent可能会出现单个item占满一个页面的情况
        ViewHolder viewHolder=new ViewHolder(view);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(FruitAdapter.ViewHolder holder, int position) {
        Fruit fruit=mFruitList.get(position);
        holder.fruitName.setText(fruit.getName());
        holder.fruitImage.setImageResource(fruit.getImageId());
    }

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

public class MainActivity extends AppCompatActivity {
    private List fruitList=new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        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<10;i++){
            Fruit apple=new Fruit("Apple",R.mipmap.ic_launcher);
            fruitList.add(apple);
        }
    }
}

2.实现横向滚动和瀑布流布局

修改fruit_item布局

修改MainActivity中的代码

public class MainActivity extends AppCompatActivity {
    private List fruitList=new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        RecyclerView recyclerView=(RecyclerView) findViewById(R.id.recycler_view);
        LinearLayoutManager layoutManager=new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter=new FruitAdapter(fruitList);
        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
        recyclerView.setAdapter(adapter);
    }
    private void initFruits(){
        for(int i=0;i<10;i++){
            Fruit apple=new Fruit("Apple",R.mipmap.ic_launcher);
            fruitList.add(apple);
        }
    }
}

除了LinearLayoutManage之外，RecyclerView还给我们提供了GridLayoutManager和StaggeredGridLayoutManager这两种内置的布局排列方式。GridLayoutManager可以用于实现网格布局，StaggeredGridLayoutManager可以用于实现瀑布流布局。这里我们实现以下效果更加炫酷的瀑布流布局。

android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="5dp"
    >
    
    android:layout_gravity="left"
        android:layout_marginTop="10dp"
        
        />

接着修改mainActivity中的代码，如下所示：

public class MainActivity extends AppCompatActivity {
    private List fruitList=new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        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<10;i++){
            Fruit apple=new Fruit(getRandomLengthName("Apple"),R.mipmap.ic_launcher);
            fruitList.add(apple);
        }
    }
    private String getRandomLengthName(String name){
        Random random=new Random();
        int length=random.nextInt(20)+1;
        StringBuilder builder=new StringBuilder();
        for(int i=0;i

效果如下

RecyclerView的点击事件

修改FruitAdapter中的代码，如下所示：

public class FruitAdapter extends RecyclerView.Adapter {

    private List mFruitList;

    static class ViewHolder extends RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
        View fruitView;
        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(ListfruitList){
        mFruitList=fruitList;
    }
    @Override
    public FruitAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,null,false);
        final ViewHolder viewHolder=new ViewHolder(view);
        viewHolder.fruitView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int position=viewHolder.getAdapterPosition();
                Fruit fruit=mFruitList.get(position);
                Toast.makeText(view.getContext(),"you clicked view"+fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
        viewHolder.fruitImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int position=viewHolder.getAdapterPosition();
                Fruit fruit=mFruitList.get(position);
                Toast.makeText(view.getContext(),"you clicked image"+fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(FruitAdapter.ViewHolder holder, int position) {
        Fruit fruit=mFruitList.get(position);
        holder.fruitName.setText(fruit.getName());
        holder.fruitImage.setImageResource(fruit.getImageId());
    }

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

参考——《第一行代码》