4.10 优化LIstView： 在listView中复用历史缓存view对象减少内存开销

问题1: 在listview中的中,在手指拖动listview,创建一个新的item的时候都会调用getView 方法，getview这个方法本身就比较消耗内存，假如listview要显示成百上千个条目，每次手指拖动时都要调用 getView方法去加载item，这是非常消耗内存的事件，会出现内存溢出

解决办法： 优化listview，复用历史缓存的view对象

问题2：在listView中   tv_number =(TextView) view.findViewById(R.id.   tv_number ); 也是一件非常消耗内存的操作

解决办法：只是在创建view对象的时候去寻找控件，然后把控件的id引用存起来，复用历史缓存的view的时候复用存起来的控件id

 

 

 

 

 

 

 

 

 

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public   class   CallSmsSafeActivity   extends   Activity {

       private   String   TAG =   "CallSmsSafeActivity" ;

       private   ListView   lv_callsms_safe ;

       private   BlackNumberDao   dao ;

       private   BlackNumberBean   blackNumberBean ;

       private   List<BlackNumberBean>   numberList   ;

       private   TextView    tv_number ;

       private   TextView    tv_mode ;

       private   ImageView   iv_delete ;

       @Override

       protected   void   onCreate(Bundle savedInstanceState) {

               super .onCreate(savedInstanceState);

            setContentView(R.layout.   activity_callsms_safe );

            

               dao =   new   BlackNumberDao(   this );

               numberList =   dao .getNumberInfo();

            

            

               lv_callsms_safe =(ListView) findViewById(R.id. lv_callsms_safe   );

               lv_callsms_safe .setAdapter(   new   MyAdapter());

            

            

      }

      

      

       /**

       * 创建适配器

       */

       public   class   MyAdapter    extends   BaseAdapter{

            

               @Override

               public   int   getCount() {

                  

                     return   numberList .size();

            }

            

            

               @Override

               public   View getView(   int   position, View convertView, ViewGroup parent) {

                  

                     //复用历史缓存view对象,减少内存消耗,防止内存溢出

                  View view=   null ;

                  ViewHolder holder=   null ;

                  

                     if (convertView!=   null &&convertView   instanceof   RelativeLayout){     //RelativeLayout:填充view的布局类型

                        view=convertView;

                        Log. i( TAG   ,   "复用历史缓存view:"   +position);

                        

                        holder=(ViewHolder) view.getTag();     //复用孩子的id

                        

                  }   else {

                        view = View. inflate(getApplicationContext(), R.layout. list_callsms_item , null   );

                        Log. i( TAG   ,   "创建新的view对象:"   +position);

                        

                        holder=   new   ViewHolder();     //初始化view持有者

                        

                           //只是在创建view的时候去寻找控件,然后把控件的id存起来

                        holder.   tv_number =(TextView) view.findViewById(R.id. tv_number   );

                        holder.   tv_mode =(TextView) view.findViewById(R.id. tv_mode   );

                        holder.   iv_delete =(ImageView) view.findViewById(R.id. iv_delete   );

                        

                        view.setTag(holder);     //将holder存到view中

                  }

                  

                     //非常消耗内存

                     //View view = View.inflate(getApplicationContext(), R.layout.list_callsms_item,null);

                  

                  

                     blackNumberBean   =   numberList .get(position);

                   holder.   tv_number .setText(   "号码:" + blackNumberBean   .getNumber());

                   String mode=   blackNumberBean .getMode();

                     if (   "1" .equals(mode)){

                         holder.   tv_mode .setText(   "电话拦截" );

                   }   else   if (   "2" .equals(mode)){

                         holder.   tv_mode .setText(   "短信拦截" );

                   }   else   if (   "3" .equals(mode)){

                         holder.   tv_mode .setText(   "全部拦截" );

                   }

                  

                     return   view;

            }

               @Override

               public   Object getItem(   int   position) {

                  

                     return   null ;

            }

               @Override

               public   long   getItemId(   int   position) {

                  

                     return   0;

            }

            

            }

      

      

      

       /**

       * 创建view持有者,将需要找的控件的应用放在 viewholder中

       */

       static   class   ViewHolder{

            

            TextView       tv_number ;

            TextView       tv_mode ;

            ImageView     iv_delete ;

      }

      

      

}