ListView 使用 BaseAdater 适配器

分手后的思念是犯贱 2022-05-10 14:36 175阅读 0赞

*  SimpleAdapter 继承 BaseAdapter ,SimpleAdapter 看做 android 帮我们实现的适配器。
 *  ViewHolder 是为了提高加载效率，为了避免每次调用 getView() 方法是都通过 findViewById 去是 实例化 控件

**效果:**  
![在这里插入图片描述][70]

#### activity\_main.xml ####

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">
    
        <ListView
            android:id="@+id/LV"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>
    </LinearLayout>

#### item\_layout.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="match_parent"
        android:orientation="horizontal">
    
        <ImageView
            android:id="@+id/img"
            android:layout_marginLeft="20dp"
            android:src="@mipmap/ic_launcher_round"
            android:layout_width="50dp"
            android:layout_height="50dp" />
    
        <TextView
            android:id="@+id/tv"
            android:gravity="center"
            android:text="你好"
            android:textSize="28sp"
            android:layout_width="wrap_content"
            android:layout_height="50dp" />
    </LinearLayout>

#### Animal 数据绑定类 ####

public class Animal {
        public Animal(String animal, int imgId) {
            this.animal = animal;
            this.imgId = imgId;
        }
    
        private String animal;
        private int imgId;
    
        public int getImgId() {
            return imgId;
        }
    
        public void setImgId(int imgId) {
            this.imgId = imgId;
        }
    
        public String getAnimal() {
            return animal;
        }
    
        public void setAnimal(String animal) {
            this.animal = animal;
        }
    }

#### AnimalAdapter ####

public class AnimalAdapter extends BaseAdapter {
        private Context context;
        private List<Animal> datas;
    
        public AnimalAdapter(Context context,List<Animal> datas)
        {
            this.context = context;
            this.datas = datas;
        }
    
    
        // 子项个数
        @Override
        public int getCount() {
            return datas.size();
        }
        // 返回子项对象
        @Override
        public Object getItem(int position) {
            return datas.get(position);
        }
    
        // 返回子项下标
        @Override
        public long getItemId(int position) {
            return position;
        }
    
        // 创建 ViewHolder 类
        class ViewHolder {
            ImageView animalImage;
            TextView animalName;
        }
        // 返回子项视图
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            Animal animal = (Animal) getItem(position);
            View view;
            ViewHolder viewHolder;
            if(convertView == null)
            {
                view = LayoutInflater.from(context).inflate(R.layout.item_layout,null);
                viewHolder = new ViewHolder();
                viewHolder.animalImage = view.findViewById(R.id.img);
                viewHolder.animalName = view.findViewById(R.id.tv);
                view.setTag(viewHolder);
            }else{
                view = convertView;
                viewHolder = (ViewHolder) view.getTag();
            }
            viewHolder.animalName.setText(animal.getAnimal());
            viewHolder.animalImage.setImageResource(animal.getImgId());
            return view;
        }
    }

#### MainActivity.java ####

public class MainActivity extends AppCompatActivity{
    
    
        private ListView listView;
        private List<Animal> datas = new ArrayList<>();
        private AnimalAdapter animalAdapter;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            initialData();
            listView = findViewById(R.id.LV);
            animalAdapter = new AnimalAdapter(this,datas);
            listView.setAdapter(animalAdapter);
            listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    Toast.makeText(MainActivity.this, datas.get(position).getAnimal(), Toast.LENGTH_SHORT).show();
                }
            });
        }
    
        private void initialData() {
            for (int i = 0; i < 20; i++) {
                datas.add(new Animal("安卓"+i,R.drawable.ic_launcher_round));
            }
        }
    }

[70]: /images/20220505/4df60761154242fcbf396d55b255dab8.png