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 }