ListView的优化

Posted 2021-01-11 sanguineboy

**ListView优化
优化一：因为getView()方法中每次都将布局重新加载了一遍，所以当ListView快速滚动的时候会影响效率
解决方法：可利用convertView参数将之前加载好的布局缓存
*优化二：在getView()方法中每次都要调用View的findViewById()方法获取一次控件的实例
解决方法：可通过新增一个类，用于对控件实例的缓存

public class MainActivity extends Activity {
    private ListView lv;
    private List<String> list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        lv = (ListView) findViewById(R.id.lv);
        
        list = new ArrayList<String>();
        for (int i = 0; i < 10; i++) {
            list.add("item"+i);
        }
        
        MyAdapter adapter = new MyAdapter();
        lv.setAdapter(adapter);
        
    }
    
    class MyAdapter extends BaseAdapter{
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return list.size();
        }

        @Override
        public Object getItem(int position) {
            // TODO Auto-generated method stub
            return list.get(position);
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder = null;
            if(convertView==null){
                LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);//获得布局填充器对象
                convertView  = inflater.inflate(R.layout.item_test, null);  //将item_test这个xml布局文件实例化成对应的view对象
                holder  = new ViewHolder();
                holder.tv = (TextView) convertView.findViewById(R.id.tv);
                convertView.setTag(holder);//利用setTag()方法对可复用的holder添加标记方便获取
            }else{
                holder = (ViewHolder) convertView.getTag();
            }
            holder.tv.setText(list.get(position));      
            return convertView;
        }   
    }
    //新定义一个内部类，用于对控件的实例进行缓存
    static class ViewHolder{
        TextView tv;
    }
}