关于RecyclerView.ViewHolder和RecyclerView.Adapter [英] About RecyclerView.ViewHolder and RecyclerView.Adapter

问题描述

1. RecyclerView.ViewHolder类的字段为public final View itemView.它说onBindViewHolder方法应该更新itemView的内容以反映给定位置的项目. final修饰符是否表示此字段的值不能更改?

1. The RecyclerView.ViewHolder class has a field that is public final View itemView. It says that the onBindViewHolder method should update the contents of the itemView to reflect the item at the given position . Doesn’t the final modifier indicate that the value of this field cannot change ?

下面的代码来自教科书:

The code below is from the textbook :

public class ViewHolder extends RecyclerView.ViewHolder {
   ...
      @Override
      public int getItemCount() {
          ...
      }
      @Override
      public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int    viewType) {
         ...
      }
      @Override
      public void onBindViewHolder(ViewHolder viewHolder, int position) {
         ...
      }
}

为什么这里的这些方法可以覆盖从RecyclerView.ViewHolder类派生的RecyclerView.Adapter类中的方法?

Why do these methods here can override the methods in the RecyclerView.Adapter class which is derived from the RecyclerView.ViewHolder class ?

https://developer.android.com/参考/android/support/v7/widget/RecyclerView.Adapter.html

https://developer.android.com/参考/android/support/v7/widget/RecyclerView.ViewHolder.html

有人可以解释吗?

谢谢.

推荐答案

最终修饰符是否表示该字段的值 不能改变?

Doesn’t the final modifier indicate that the value of this field cannot change ?

视图上的最终修饰符表示您只能仅启动一次视图(通过创建新的视图(上下文)或从xml文件中填充视图). 但是您仍然可以修改view属性. (即您的视图包含TextView，您可以设置文本)

The final modifier on a View indicate that you can only initiate the view once (by creating a new View(context) or inflate a view from an xml file). But you can still modify the view property. (i.e. your view contains a TextView, you can set the text)

对于第二个问题，教科书中关于如何使用视图保持器实现适配器的定义不是很精确.这是带有自定义视图持有人的适配器的简单实现.

For your second question, the text book is not very precise about how to implement the adapter with a view holder. Here is a simple implementation of an adapter with a custom view holder.

public class Adapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder>{

    private List<String> titles;

    public Adapter(List<String> titles) {
        this.titles = titles;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        return new MyViewHolder(LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item_view, viewGroup, false));
    }

    @Override
    public void onBindViewHolder(MyViewHolder myViewHolder, int i) {
        String title = titles.get(i);
        myViewHolder.title.setText(title);
    }

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

    public static class MyViewHolder extends RecyclerView.ViewHolder {

        TextView title;

        public MyViewHolder(View itemView) {
            super(itemView);

            title = (TextView) itemView.findViewById(R.id.title_TV);
        }
    }

}

以及它的xml文件:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <TextView
        android:id="@+id/title_tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</RelativeLayout>

您可以看到，如果扩展RecyclerView.Adapter，则必须重写这3种方法.

You can see that if you extend RecyclerView.Adapter, you will have to override these 3 methods.

希望这将帮助您更多地了解RecyclerView.

Hope this will help you to understand more the RecyclerView.

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