ListView的简单使用

<?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">
    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >
    </ListView>
</LinearLayout>

public class Fruit {
    private String name ;
    private int imageId;
    public Fruit(int imageId, String name) {
        this.imageId = imageId;
        this.name = name;
    }
    public int getImageId() {
        return imageId;
    }
    public String getName() {
        return name;
    }

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >
    <ImageView
        android:id="@+id/fruit_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/Tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="50dp"/>
</LinearLayout>

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;
    public FruitAdapter(Context context , int textViewResourceId, List<Fruit> objects){
       super(context,textViewResourceId,objects);
       this.resourceId = textViewResourceId;
   }
    @NonNull
    @Override
    //每个子项被滚动到屏幕内会调用这个方法
    //concertView 参数，用于将之前加载好的布局进行缓存，以便进行重用
    public View getView(int position, View convertView, @NonNull ViewGroup parent) {
        Fruit fruit = getItem(position);
        View view ;
        ViewHolder viewHolder ;
        //如果convertView 为null，则加载布局，不为空则对convertView进行重用，避免了每次加载布局
        //加入一个内部类ViewHolder 用于对控件的实例进行缓存，避免了每次都要加载控件的实例
        //这样就提高了ListView 的运行效率
        if(convertView == null){
            view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.fruitImage=(ImageView)view.findViewById(R.id.fruit_item);
            viewHolder.fruitName=(TextView) view.findViewById(R.id.Tv);
            view.setTag(viewHolder); //将viewHolder 存储在View中
        }else{
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
    }
    class ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
    }
}

public class MainActivity extends AppCompatActivity {
    List<Fruit> list ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView listView =(ListView)findViewById(R.id.lv);
        init();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,
                R.layout.fruit_item,list);
        listView.setAdapter(adapter);
    }
    private void init() {
        list = new ArrayList<>();
        for (int i = 1 ;i<= 50 ;i++){
            Fruit f = new Fruit(R.drawable.tab_2,"name"+i);
            list.add(f);
        }
    }
}