Android中针对ListView的性能优化

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/fruit_image"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/fruit_name"
        android:layout_marginLeft="10dp"
        android:layout_gravity="center_vertical"/>

</LinearLayout>

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

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

    public String getName() {
        return name;
    }

    public int getImageId() {
        return imageId;
    }
}

public class MainActivity extends AppCompatActivity {
    private List<Fruit> fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruit();//初始化水果数据
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
//        ArrayAdapter<String> adapter = new ArrayAdapter<String>(
//            MainActivity.this,android.R.layout.simple_list_item_1,data);
        ListView listView = (ListView)findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }
    private void initFruit(){
        for(int i = 0;i<2;i++){
            Fruit apple = new Fruit("Apple",R.drawable.apple_1);//图片的名字不能以数字开头
            fruitList.add(apple);
            Fruit banana = new Fruit("Banana",R.drawable.banana_2);
            fruitList.add(banana);
            Fruit orange = new Fruit("orange",R.drawable.orange_3);
            fruitList.add(orange);
            Fruit watermelon = new Fruit("watermelon",R.drawable.watermelon);
            fruitList.add(watermelon);
            Fruit pear = new Fruit("pear",R.drawable.pear);
            fruitList.add(pear);
            Fruit grape = new Fruit("grape",R.drawable.grape);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("pineapple",R.drawable.pineapple);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("strawberry",R.drawable.strawberry);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit("cherry",R.drawable.cherry);
            fruitList.add(cherry);
            Fruit mango = new Fruit("mango",R.drawable.mango);
            fruitList.add(mango);
        }
    }
}

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;

    public FruitAdapter(Context context, int textViewResourceId,List<Fruit> objects) {
        super(context, textViewResourceId, objects);
        resourceId = textViewResourceId;
    }
    //以下使用ViewHolder进行进一步优化
    @Override
    public View getView(int position,View convertView,ViewGroup parent) {
        Fruit fruit = getItem(position);//获取当前的fruit实例
        View view;
        ViewHolder viewHolder;
        //converView用于缓存之前加载好的布局
        if(convertView == null){
            view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.fruitImage = (ImageView)view.findViewById(R.id.fruit_image);
            viewHolder.fruitName = (TextView)view.findViewById(R.id.fruit_name);
            view.setTag(viewHolder);//将viewHolder存储在view中
        }else{
            view = convertView;
            viewHolder = (ViewHolder)view.getTag();//重新获取ViewHolder
        }
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
    }
    class ViewHolder
    {
        ImageView fruitImage;
        TextView fruitName;
    }
    //通过判空，可大大优化性能
/*    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Fruit fruit = getItem(position);//获取当前的fruit实例
        View view;
        //converView用于缓存之前加载好的布局
        if(convertView == null){
            view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
        }else{
            view = convertView;
        }
        //false表示只让我们在父布局中声明的layout属性生效，但不位这个view添加父布局
        ImageView fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
        TextView fruitName = (TextView)view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());
        fruitName.setText(fruit.getName());
        return view;
    }*/

}