FC 3.5.3提升listview的运行效率

• convertView
• ViewHolder

在普通的listview中，自定义的adapter里的getview方法，每次都会将布局重新加载了一遍，其实没有必要，使用convertView对加载好的布局进行缓存，以后的进行重用即可。

使用ViewHolder，用于对控件的实例进行缓存。当convertView为null时，创建一个ViewHolder对象，将控件的实例存放在ViewHolder里，然后调用view的settag方法，将ViewHolder存放在view中。当convertView不为null时，调用ViewHolder的gettag方法，将ViewHolder重新取出。

public class FruitAdapter extends ArrayAdapter<Fruit> {

    private int resourceId;

    public FruitAdapter(Context context, int textViewResourceId,
                        List<Fruit> objects) {
        super(context, textViewResourceId, objects);
        resourceId = textViewResourceId;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Fruit fruit = getItem(position); // 获取当前项的Fruit实例
        View view;
        ViewHolder viewHolder;
        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;
    }

}