listview 优化

ListView的优化：

（前两点都是利用ListView的自身优化机制优化【缓存优化】）

1.利用ListView自身的缓存机制，他会缓存条目中的一个条目item，当listview第一屏显示完成之后，就会出现一个缓存条目，其实就是BaseAdapter里面的public View getView(int position, View convertView, ViewGroup parent)。

2.减少findViewById()的次数，findViewById是一个相对比较耗性能的操作，因为这个操作每次都需要到布局中去查找文件。把item里面的控件封装成一个javaBean，当item条目被加载的时候就去找到对应的控件。

3.利用时间去换取时间，比如开机优化，把一些重要的程序先启动了，启动完系统之后再启动其他程序。

4.利用空间去换取时间，把要获取的数据先加载到内存里面，再处理数据的时候，直接从内存中获取。

例如：减少数据库的频繁打开和关闭和减少查询的次数。

Demo：需求： 程序锁，将手机中所有的应用显示出来，是否是带锁的应用用数据库进行存储，通过ListView显示。

  3 import java.util.List;
  5 import android.app.Activity;
  6 import android.os.Bundle;
  7 import android.os.Handler;
  8 import android.os.Message;
  9 import android.util.Log;
 10 import android.view.LayoutInflater;
 11 import android.view.View;
 12 import android.view.ViewGroup;
 13 import android.view.animation.TranslateAnimation;
 14 import android.widget.AdapterView;
 15 import android.widget.AdapterView.OnItemClickListener;
 16 import android.widget.BaseAdapter;
 17 import android.widget.ImageView;
 18 import android.widget.ListView;
 19 import android.widget.RelativeLayout;
 20 import android.widget.TextView;
 21
 22 import com.android.hzy.mobilesafe.R;
 23 import com.android.hzy.mobilesafe.dao.AppLockDao;
 24 import com.android.hzy.mobilesafe.domain.AppInfo;
 25 import com.android.hzy.mobilesafe.engine.AppInfoService;
 26
 27 public class AppLockManagerActivity extends Activity {
 28
 29     protected static final int SUCCESS_GET_APPLICATION = 0;
 30     private ListView lv_applockmanager;
 31     private RelativeLayout rl_loading;
 32     private AppInfoService appInfoService;
 33     private List<AppInfo> appInfos;
 34
 35     private List<String> appLocks; // 程序锁应用集合
 36
 37     private AppLockManagerAdapter mAdapter;
 38     private AppLockDao appLockDao;
 39     private Handler mHandler = new Handler(){
 40
 41         public void handleMessage(Message msg) {
 42             switch (msg.what) {
 43             case SUCCESS_GET_APPLICATION:
 44                 appLocks = appLockDao.findAll();
 45                 mAdapter = new AppLockManagerAdapter();
 46                 lv_applockmanager.setAdapter(mAdapter);
 47                 rl_loading.setVisibility(View.GONE);
 48                 break;
 49
 50             default:
 51                 break;
 52             }
 53         }
 54
 55     };
 56
 57     @Override
 58     protected void onCreate(Bundle savedInstanceState) {
 59         // TODO Auto-generated method stub
 60         super.onCreate(savedInstanceState);
 61         setContentView(R.layout.app_lock_manager);
 62
 63         lv_applockmanager = (ListView) findViewById(R.id.lv_applockmanager);
 64         rl_loading = (RelativeLayout) findViewById(R.id.rl_loading);
 65         appInfoService = new AppInfoService(this);
 66
 67         new Thread() {
 68             public void run() {
 69                 appInfos = appInfoService.getAppInfos();
 70                 Message msg = new Message();
 71                 msg.what = SUCCESS_GET_APPLICATION;
 72                 mHandler.sendMessage(msg);
 73             };
 74         }.start();
 75
 76         appLockDao = new AppLockDao(this);
 77
 78         lv_applockmanager.setOnItemClickListener(new MyOnItemClickListener());
 79     }
 80
 81     /**********listview条目点击事件*************************/
 82     private final class MyOnItemClickListener implements OnItemClickListener{
 83
 84         @Override
 85         public void onItemClick(AdapterView<?> parent, View view, int position,
 86                 long id) {
 87             // TODO Auto-generated method stub
 88             // 通过ViewHolder的iv_lock 减少findViewById
 89             ImageView iv_lock = ((ViewHolder)view.getTag()).iv_lock;
 90             AppInfo appInfo = (AppInfo) mAdapter.getItem(position);
 91 //            boolean isLockApp = appLockDao.isLockApp(appInfo.getPackagename()); 减少数据库的查询
 92             boolean isLockApp = appLocks.contains(appInfo.getPackagename());
 93             if (isLockApp) {
 94                 // 如果有锁  就解锁
 95                 appLockDao.delete(appInfo.getPackagename());
 96                 // 解锁需要将集合中带锁应用的移除
 97                 appLocks.remove(appInfo.getPackagename());
 98                 iv_lock.setImageResource(R.drawable.unlock);
 99             } else {
100                 // 如果没有锁  就加锁
101                 appLockDao.add(appInfo.getPackagename());
102                 // 加锁需要将有锁的集合中添加该应用
103                 appLocks.add(appInfo.getPackagename());
104                 iv_lock.setImageResource(R.drawable.lock);
105             }
106
107             // 设置动画
108             TranslateAnimation animation = new TranslateAnimation(0, 80, 0, 0);
109             animation.setDuration(300);
110             view.startAnimation(animation);
111         }
112
113     }
114
115     /**
116      * 适配器
117      */
118     public final class AppLockManagerAdapter extends BaseAdapter{
119
120         private LayoutInflater mInflater;
121
122         public AppLockManagerAdapter() {
123             // TODO Auto-generated constructor stub
124             mInflater = getLayoutInflater();
125         }
126
127         @Override
128         public int getCount() {
129             // TODO Auto-generated method stub
130             return appInfos.size();
131         }
132
133         @Override
134         public Object getItem(int position) {
135             // TODO Auto-generated method stub
136             return appInfos.get(position);
137         }
138
139         @Override
140         public long getItemId(int position) {
141             // TODO Auto-generated method stub
142             return position;
143         }
144
145         @Override
146         public View getView(int position, View convertView, ViewGroup parent) {
147             // TODO Auto-generated method stub
148             View view = null;
149             ViewHolder holder = null;
150             if (convertView != null) {
151                 view = convertView;
152                 holder = (ViewHolder) view.getTag();
153                 Log.i("i", " convertView != null  缓存不等于空  使用缓存");
154
155             } else {
156                 Log.i("i", " convertView == null  缓存等于空");
157                 view = mInflater.inflate(R.layout.app_lock_manager_item, null);
158                 holder = new ViewHolder();
159                 holder.iv_appicon = (ImageView) view.findViewById(R.id.iv_appicon);
160                 holder.tv_appname = (TextView) view.findViewById(R.id.tv_appname);
161                 holder.iv_lock = (ImageView) view.findViewById(R.id.iv_lock);
162                 view.setTag(holder);
163             }
164             AppInfo appInfo = appInfos.get(position);
165
166             ImageView iv_appicon = holder.iv_appicon;
167             TextView tv_appname = holder.tv_appname;
168             ImageView iv_lock = holder.iv_lock;
169
170             iv_appicon.setImageDrawable(appInfo.getApp_icon());
171             tv_appname.setText(appInfo.getApp_name());
172
173 //            boolean isLockApp = appLockDao.isLockApp(appInfo.getPackagename());
174             boolean isLockApp = appLocks.contains(appInfo.getPackagename()); // 此功能优化后  不用每次查询数据库 直接将所有有锁的程序都放入集合中存储
175             if(isLockApp){
176                 iv_lock.setImageResource(R.drawable.lock);
177             }else{
178                 iv_lock.setImageResource(R.drawable.unlock);
179             }
180
181             return view;
182         }
183
184     }
185
186     static class ViewHolder{
187         ImageView iv_appicon;
188         TextView tv_appname;
189         ImageView iv_lock;
190     }
191 }