RecyclerView

更加强大的滚动控件 RecyclerView #P123

基本用法

• 需要在build.gradle添加依赖库 recyclerview
• activity_main.xml文件添加RecyclerView
• 图片,Furit类,fruit_item.xml

• 新建FruitAdapter类,作为适配器,继承自RecyclerView.Adapter ,并且泛型指定为FruitAdapter.ViewHolder ViewHolder是内部类
  xml
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />


  新建FruitAdapter

  1. 定义内部类ViewHoler ,继承自RecyclerView.ViewHolder
  2. ViewHoler的构造函数传入一个View参数,这个参数通常就是RecyclerView子项的最外层布局,通过findViewById() 方法来获取布局中的Imageiew和TextView的实例
  3. FruitAdapter 中也有构造函数,这个方法用于把要展示的数据源传进来,并赋值给一个全部变量mFruitList

  4. FruitAdapter继承自RecyclerView.Adapter,所以要重写onCreatViewHolder(),onBingViewHolder(),getItemCount()

     1. onCreatViewHolder()用来创建ViewHolder实例,将fruit_item布局加载进来,然后创建一个ViewHoler实例,并把加载出来的布局传入构造函数中,最后将ViewHoler的实例返回
     2. onBingViewHolder()用于对RecyclerView子项的数据进行赋值,会在每个子项被滚动到屏幕内的时候执行,通过position 参数得到当前项的Fruit实例,然后将数据设置到ViewHolder的ImageView和TextView当中即可
     3. getItemCount() 告诉RecyclerView有多少子项 ,返回 mFruitList.size()
        

        public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {
        private List<Fruit> mFruitList;
        
        /**
         * Created by Mason on 2017/11/16.
         */
        
        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 getItemCount() {
            return mFruitList.size();
        }
        }

改变为横向RecyclerView

• fruit_item.xml 的LinearLayout布局改为orientation:"vertical" 垂直布局 ,默认horizontal水平布局
• 修改TextView和ImageView的layout_gravity 修改成水平居中center_horizontal

• MainActivity.java文件 调用LinearLayoutManager的setOrientation()方法设置布局排列方向 添加layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL)

  • xml
    “`xml
    

RecyclerView 点击事件

• 需要自己给子项具体的View注册点击事件
• 虽然比ListView繁琐,但是ListView给单独按钮注册事件更加繁琐
  
  1. 修改ViewHolder,添加fruitView变量来保存子项最外层布局的实例
  2. 然后在onCreatViewHolder()方法中注册点击事件就行了.
  3. 这里项目分别为最外层布局和Image注册了点击事件.

• RecyclerView强大在于,可以轻松实现子项中任意控件或布局的点击事件

  1. 我们先获取用户点击的position
  2. 通过position拿到相应的Fruit实例
  3. 再使用Toast弹出两种不同的内容
     

     public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {
        private List<Fruit> mFruitList;
     
        /**
         * Created by Mason on 2017/11/16.
         */
     
        static class ViewHolder extends RecyclerView.ViewHolder {
            View fruitView;  // 添加
            ImageView fruitImage;
            TextView fruitName;
     
            public ViewHolder(View view) {
                super(view);
                fruitView = view;  //添加
                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);
            final ViewHolder holder = new ViewHolder(view);  // 添加
            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 click 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 click image   " + fruit.getName(), Toast.LENGTH_SHORT).show();
                }
            });
            return holder;
        }
        ...
     }

  这是我学习Android的笔记,参考书<<第一行代码-第二版>>,感谢郭霖大神
  如有不足之处,可以一起讨论
  附上郭霖的blog http://blog.youkuaiyun.com/guolin_blog