android 设置默认launcher 附上代码

当系统初始化完毕后会进入homeactivity：
具体代码流程：
ActivityManagerService.java -->
public void systemReady(final Runnable goingCallback) {
...
mMainStack.resumeTopActivityLocked(null);
...
}

ActivityStack.java
final boolean resumeTopActivityLocked(ActivityRecord prev) {
        return resumeTopActivityLocked(prev, null);
    }

final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) {
...
return mService.startHomeActivityLocked(mCurrentUser); //开始启动homeactivity了，
...
}

然后我们可以在最开始加入一个自己写的接口，来设置默认launcher：
boolean startHomeActivityLocked(int userId) {
    ...
    setDefaultLauncher();
    ...

}

private void setDefaultLauncher() {
        // get default component
        String packageName = "com.android.launcher";//默认launcher包名
        String className = "com.android.launcher2.Launcher";////默认launcher入口
        Slog.i(TAG, "defautl packageName = " + packageName + ", default className = " + className);
        if ((packageName != null && packageName.trim().length() > 1) && (className != null && className.trim().length() > 0)) {
            boolean firstLaunch = SystemProperties.getBoolean("persist.sys.sw.firstLaunch", true);  //只做一次 可以注意这几个变量firstLaunch mFirstLaunch
            Slog.d(TAG, "firstLaunch = " + firstLaunch);
            if(firstLaunch){
                mFirstLaunch = true;
                // do this only for the first boot
                SystemProperties.set("persist.sys.sw.firstLaunch", "false");
            }
            Slog.d(TAG, "firstLaunch = " + firstLaunch);
            if(mFirstLaunch){
                IPackageManager pm = ActivityThread.getPackageManager();

                //清除当前默认launcher
                ArrayList<IntentFilter> intentList = new ArrayList<IntentFilter>();
                ArrayList<ComponentName> cnList = new ArrayList<ComponentName>();
                mContext.getPackageManager().getPreferredActivities(intentList, cnList, null);
                IntentFilter dhIF;
                for(int i = 0; i < cnList.size(); i++)
                {
                    dhIF = intentList.get(i);
                    if(dhIF.hasAction(Intent.ACTION_MAIN) &&
                    dhIF.hasCategory(Intent.CATEGORY_HOME))
                    {
                        mContext.getPackageManager().clearPackagePreferredActivities(cnList.get(i).getPackageName());
                    }
              }

                //获取所有launcher activity
                Intent intent = new Intent(Intent.ACTION_MAIN);
                intent.addCategory(Intent.CATEGORY_HOME);
                List<ResolveInfo> list = new ArrayList<ResolveInfo>();
                try
                {
                    list = pm.queryIntentActivities(intent,
                        intent.resolveTypeIfNeeded(mContext.getContentResolver()),
                        PackageManager.MATCH_DEFAULT_ONLY,UserHandle.getCallingUserId());
                }catch (RemoteException e) {
                    throw new RuntimeException("Package manager has died", e);
                }
                // get all components and the best match
                IntentFilter filter = new IntentFilter();
                filter.addAction(Intent.ACTION_MAIN);
                filter.addCategory(Intent.CATEGORY_HOME);
                filter.addCategory(Intent.CATEGORY_DEFAULT);
                final int N = list.size();
                Slog.d(TAG, "N:::::hyhyhyhy:::: = " + N);
                ComponentName[] set = new ComponentName[N];
                int bestMatch = 0;
                for (int i = 0; i < N; i++)
                {
                    ResolveInfo r = list.get(i);
                    set[i] = new ComponentName(r.activityInfo.packageName,
                                    r.activityInfo.name);
                    Slog.d(TAG, "r.activityInfo.packageName:::::hyhyhyhy:::: = " + r.activityInfo.packageName);
                    Slog.d(TAG, "r.activityInfo.name:::::hyhyhyhy:::: = " + r.activityInfo.name);
                    if (r.match > bestMatch) bestMatch = r.match;
                }
                //设置默认launcher
                ComponentName launcher = new ComponentName(packageName, className);
                try
                {
                    pm.addPreferredActivity(filter, bestMatch, set, launcher,UserHandle.getCallingUserId());
                } catch (RemoteException e) {
                    throw new RuntimeException("Package manager has died", e);
                }
            }
        }
    }