《第一行代码》 随手笔记——第三章 UI开发的点点滴滴

 3.5.3提升ListView的运行效率

  1、View view;
if (convertView == null) {
view = LayoutInflater.from(getContext()).inflate(resourceId, null);
} else {
view = convertView;
}

2、每次在getView()方法中还是会调用View的findViewById()方法来获取一次控件的实例。我们可以借助一个ViewHolder来对这部分性能进行优化

public class FruitAdapter extends ArrayAdapter<Fruit> {
……
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position);
View view;
ViewHolder viewHolder;
if (convertView == null) {
view = LayoutInflater.from(getContext()).inflate(resourceId, null);
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;

}
}