froyo系统原生bug及修正:改变系统语言时Launcher2的AllApps内shortcut不刷新

把froyo的Launcher2移植到eclair后,产生了一些小问题,都一一解决掉了.这是市场反馈回来的一个问题之一,摸清内部机制颇废了一番周折.也算见识了android系统内部的另一个面向切面编程案例,很有必要记录一下,有时间好好研究研究,可以借此做些特殊的系统功能.

严格意义上说,这并不是跨版本移植产生的问题,而是系统原生的一个bug,用samsung的galaxy tab平板模拟器测试同样是此现象:当在Launcher里面启动Settings,改变语言设置后,再回到Launcher,AllApps2D里面的shortcuts文字部分并不随之更新,还是保持原样.其它部分却已更新.

察看Settings源码可以知道,设置语言,改变的只是执行了如下代码:

Java代码

1. try { 
2.     IActivityManager am = ActivityManagerNative.getDefault(); 
3.     Configuration config = am.getConfiguration(); 
4.  
5.     Loc loc = mLocales[position]; 
6.     config.locale = loc.locale; 
7.  
8.     // indicate this isn't some passing default - the user wants this remembered 
9.     config.userSetLocale = true; 
10.  
11.     am.updateConfiguration(config); 
12.     // Trigger the dirty bit for the Settings Provider. 
13.     BackupManager.dataChanged("com.android.providers.settings"); 
14. } catch (RemoteException e) { 
15.     // Intentionally left blank 
16. } 
17. finish(); 

        try {            IActivityManager am = ActivityManagerNative.getDefault();            Configuration config = am.getConfiguration();            Loc loc = mLocales[position];            config.locale = loc.locale;            // indicate this isn't some passing default - the user wants this remembered            config.userSetLocale = true;            am.updateConfiguration(config);            // Trigger the dirty bit for the Settings Provider.            BackupManager.dataChanged("com.android.providers.settings");        } catch (RemoteException e) {            // Intentionally left blank        }        finish();

在configuration改变后,系统会让每一个切换到前台的Activity destroy,然后重新加载至原位置,非常奇妙的刷新操作,有时间要看看他如何保存当前状态的代码,比如,当前切换到前台的Activity是launcher,则会一直加载到allapps2d打开,而不是oncreate完成后的初始位置.对于状态机学习来说,Launcher无疑是很好的教科书.

然而,configuration的控制范围只是所有的Activity,Activity实现了一个接口ComponentCallbacks,里面有:

Java代码

1. /**
2. * Called by the system when the device configuration changes while your
3. * activity is running.  Note that this will <em>only</em> be called if
4. * you have selected configurations you would like to handle with the
5. * {@link android.R.attr#configChanges} attribute in your manifest.  If
6. * any configuration change occurs that is not selected to be reported
7. * by that attribute, then instead of reporting it the system will stop
8. * and restart the activity (to have it launched with the new
9. * configuration).
10. *
11. * <p>At the time that this function has been called, your Resources
12. * object will have been updated to return resource values matching the
13. * new configuration.
14. *
15. * @param newConfig The new device configuration.
16. */ 
17. public void onConfigurationChanged(Configuration newConfig) { 
18.     mCalled = true; 
19.  
20.     if (mWindow != null) { 
21.         // Pass the configuration changed event to the window 
22.         mWindow.onConfigurationChanged(newConfig); 
23.     } 
24. } 

    /**     * Called by the system when the device configuration changes while your     * activity is running.  Note that this will <em>only</em> be called if     * you have selected configurations you would like to handle with the     * {@link android.R.attr#configChanges} attribute in your manifest.  If     * any configuration change occurs that is not selected to be reported     * by that attribute, then instead of reporting it the system will stop     * and restart the activity (to have it launched with the new     * configuration).     *      * <p>At the time that this function has been called, your Resources     * object will have been updated to return resource values matching the     * new configuration.     *      * @param newConfig The new device configuration.     */    public void onConfigurationChanged(Configuration newConfig) {        mCalled = true;        if (mWindow != null) {            // Pass the configuration changed event to the window            mWindow.onConfigurationChanged(newConfig);        }    }

而对于Launcher来说,allapps里面的内容是通过LauncherModel.java里面的线程类去异步加载的,重启Launcher这个Activity,并不会让LauncherModel里面的缓存的allapps内容刷新,Launcher是直接拿了LauncherModel里面缓存的query数据而不是通知loader线程重新获取,问题就出在这里了.

解决的方法并不复杂,Launcher在调onCreate()的时候,会调用checkForLocaleChange()方法检查是否语言设置是否被修改,我们定义一个boolean类变量,把语言设置是否改变存到里面,然后为LauncherModel重构一个startLoader方法,在onCreat()代码的相应位置调用此重构方法,把状态值传进去.在内部类Loader的loadAndBindAllApps()方法里,增加判断条件让语言改变时走loadAllAppsByBatch()路线即可.

我们来看看可以从中学到些什么?

1\定义和使用configuration的类变量,可以很好的传递任何全局数据,可以和硬件方便的通信.

2\利用configuration控制framework各模块ui.一个简单例子,在launcher中,利用语言设置变化,显示或隐藏不同语言环境的应用,比如面向国内市场的机器,youtube反正用不上,就可以隐藏掉.加上youku.平板电脑没有phone功能的,把phone的shortcut给拿掉.

3\另一个想法,能否利用configuration绕过系统权限实现截屏等需要root权限的功能?