Android基础——RecyclerView

RecyclerView是什么？

RecyclerView是进阶版的ListView，不仅可以实现ListView的纵向滑动，还可以横向滑动和瀑布流滑动。

RecyclerView使用

使用RecyclerView需要在build.gradle中添加相应的依赖库：

implementation "androidx.recyclerview:recyclerview:1.2.1"

在activity_main.xml中添加RecyclerView控件

<androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycle_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

准备数据，创建bean类：

public class Data {
    private String name;
    private int imageId;

    public Data(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImageId() {
        return imageId;
    }

    public void setImageId(int imageId) {
        this.imageId = imageId;
    }
}

创建适配布局list_item.xml：

<?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="wrap_content">
    <ImageView
        android:id="@+id/recycle_view_iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <TextView
        android:id="@+id/recycle_view_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

创建适配布局的适配器RecyclerViewAdapter继承RecyclerView.Adapter<T>，重写相关方法，其中：

1. T为内部类ViewHolder继承，用于RecyclerView.ViewHolder，传入参数为适配布局的View实例
2. 构造方法用于接收并维护数据
3. onCreateViewHolder()加载适配布局传入ViewHolder并返回，viewType用于和getItemViewType()根据不同数据返回对应布局，如设置Header
4. onBindViewHolder()用于将控件和数据进行绑定
5. getItemCount()用于返回数据长度

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {

    private List<Data> mDataList;

    public class ViewHolder extends RecyclerView.ViewHolder {
        ImageView DataIv;
        TextView DataTv;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            DataIv = itemView.findViewById(R.id.recycle_view_iv);
            DataTv = itemView.findViewById(R.id.recycle_view_tv);
        }
    }
    
    public RecyclerViewAdapter(List<Data> mDataList) {
        this.mDataList = mDataList;
    }

    
    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Data data = mDataList.get(position);
        holder.DataIv.setImageResource(data.getImageId());
        holder.DataTv.setText(data.getName());
    }

    @Override
    public int getItemCount() {
        if(mDataList != null){
        	return mDataList.size();
    	}
    	return 0;
    }
}

修改MainActivity，为RecyclerView设置布局方向和适配器

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycle_view);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(linearLayoutManager);
        List<Data> dataList = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            Data data = new Data("data"+i,R.mipmap.ic_launcher);
            dataList.add(data);
        }
        RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(dataList);
        recyclerView.setAdapter(recyclerViewAdapter);
    }
}

效果图：

瀑布流滚动

修改适配布局list_item.xml中的LinearLayout父布局，设置为垂直排列：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/recycle_view_iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <TextView
        android:id="@+id/recycle_view_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

将LinearLayoutManager修改为StaggeredGridLayoutManager即可修改为瀑布流，瀑布流的宽度是由布局的列数自动适配的，这里的列数为3：

StaggeredGridLayoutManager layoutManager=new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);

效果图（当图片和文字不一时才会显示的更好看，类似小红书）：

横向滚动

修改适配布局list_item.xml中的LinearLayout父布局，将宽度控制为100，避免过大：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="100dp"
    android:orientation="vertical"
    android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/recycle_view_iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <TextView
        android:id="@+id/recycle_view_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

修改MainAcitivity中的代码，在创建LinearLayoutManager后通过setOrientation方法修改为横向滚动

layoutManager.setOrientation(RecyclerView.HORIZONTAL);

效果图：

RecyclerView点击事件

RecyclerView的点击事件需要分别给各个子控件设置，在Viewholder类中创建成员变量维护适配布局的View，在onCreateViewHolder()给最外层布局和ImageView设置点击事件：

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {

    private List<Data> mDataList;

    public class ViewHolder extends RecyclerView.ViewHolder {
        ImageView DataIv;
        TextView DataTv;
        View ItemView;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            ItemView = itemView;
            DataIv = itemView.findViewById(R.id.recycle_view_iv);
            DataTv = itemView.findViewById(R.id.recycle_view_tv);
        }
    }

    public RecyclerViewAdapter(List<Data> mDataList) {
        this.mDataList = mDataList;
    }


    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
        final ViewHolder holder = new ViewHolder(view);
        holder.ItemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAbsoluteAdapterPosition();
                Data data = mDataList.get(position);
                Toast.makeText(v.getContext(), "click"+data.getName(), Toast.LENGTH_SHORT).show();
            }
        });
        holder.DataIv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

            }
        });

        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Data data = mDataList.get(position);
        holder.DataIv.setImageResource(data.getImageId());
        holder.DataTv.setText(data.getName());
    }

    @Override
    public int getItemCount() {
    	if(mDataList != null){
        	return mDataList.size();
    	}
    	return 0;
    }
}