设置default Launcher

系统有多个Launcher时，会在packages.xml 设置如下信息:
/data/system/packages.xml
<preferred-activities>
<item name="com.android.ulauncher/.Launcher" match="100000" set="2">
<set name="com.android.launcher/com.android.launcher2.Launcher" />
<set name="com.android.ulauncher/.Launcher" />
<filter>
<action name="android.intent.action.MAIN" />
<cat name="android.intent.category.HOME" />
<cat name="android.intent.category.DEFAULT" />
</filter>
</item>
</preferred-activities>

如何在启动时自动设置default Launcher呢？

在PackageManagerService构造函数中，会读取packages.xml文件：mRestoredSettings = mSettings.readLPw();
所以在之前添加设置：
readPermissions();
            
String firstBoot = SystemProperties.get("persist.sys.preactivity"); 
if ("0".equals(firstBoot)) {
    addPreferredActivityForULauncher();
}
SystemProperties.set("persist.sys.preactivity", "1");

mRestoredSettings = mSettings.readLPw();

private void addPreferredActivityForULauncher() {
    IntentFilter filter = new IntentFilter();
    filter.addAction("android.intent.action.MAIN");
    filter.addCategory("android.intent.category.HOME"); 
    filter.addCategory("android.intent.category.DEFAULT");
    ComponentName preActivity = new ComponentName("com.android.ulauncher", "com.android.ulauncher.Launcher"); 
    ComponentName[] set = new ComponentName[] {new ComponentName("com.android.launcher", "com.android.launcher2.Launcher"), preActivity}; 
    mSettings.mPreferredActivities.addFilter(
            new PreferredActivity(filter, IntentFilter.MATCH_CATEGORY_EMPTY, set, preActivity));
    scheduleWriteSettingsLocked();

}

别的应用程序也可以类似这样来设置。