之前分析了安卓开机启动流程，详细可以查看Zygote和SystemServer相关的博客。系统开机经由init进程拉起后，调用Zygote孵化器开启SystemServer服务，其中系统核心重要的服务都在SystemServer中加载完成，之后便进入各个服务的SystemReady状态。由此，我们从这里开始分析。
源码分析之Launcher启动流程
具体流程分析
AMS进入SystemReady状态
ActivityManagerService启动完成后，便进入SystemReady状态，代码如下：
--> /frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public void systemReady(final Runnable goingCallback) {
...
// Start up initial activity.
mBooting = true;
// 以当前userid，启动主页
startHomeActivityLocked(mCurrentUserId, "systemReady");
...
}
AMS的systemReady中有很多复杂的逻辑，例如广播发送，工厂模式的判定等，这里我们只关心主页的启动。通过startHomeActivityLocked以当前userid启动主页。
startHomeActivityLocked
boolean startHomeActivityLocked(int userId, String reason) {
//工厂模式启动失败
if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
&& mTopAction == null) {
return false;
}
// 获取主页意图
Intent intent = getHomeIntent();
ActivityInfo aInfo =
resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
if (aInfo != null) {
intent.setComponent(new ComponentName(
aInfo.applicationInfo.packageName, aInfo.name));
// Don't do this if the home app is currently being
// instrumented.
aInfo = new ActivityInfo(aInfo);
aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
ProcessRecord app = getProcessRecordLocked(aInfo.processName,
aInfo.applicationInfo.uid, true);
if (app == null || app.instrumentationClass == null) {
intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
// 根据获取的intent，启动主页应用
mStackSupervisor.startHomeActivity(intent, aInfo, reason);
}
}
return true;
}
通过给定intent过滤信息，通过调用resolveActivityInfo检索出合适的主页应用，回传回来ActivityInfo，然后初始化新应用的相关信息，调用mStackSupervisor.startHomeActivity启动主页。
--> /frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
Intent getHomeIntent() {
Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
intent.setComponent(mTopComponent);
if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
intent.addCategory(Intent.CATEGORY_HOME);
}
return intent;
}
resolveActivityInfo筛选合适的应用信息
resolveActivityInfo中判断系统是否处于工厂模式，如果是，直接根据ComponentName调用PMS的getActivityInfo来获取应用信息；如果不是，则调用PMS的resolveIntent全局筛选合适的主页应用。
private ActivityInfo resolveActivityInfo(Intent intent, int flags, int userId) {
ActivityInfo ai = null;
ComponentName comp = intent.getComponent();
try {
if (comp != null) {
// 工厂模式
ai = AppGlobals.getPackageManager().getActivityInfo(comp, flags, userId);
} else {
// 调用PMS全局筛选合适的主页应用
ResolveInfo info = AppGlobals.getPackageManager().resolveIntent(
intent,
intent.resolveTypeIfNeeded(mContext.getContentResolver()),
flags, userId);
if (info != null) {
ai = info.activityInfo;
}
}
} catch (RemoteException e) {
}
return ai;
}
PMS筛选主页应用信息
-->/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
AMS通过Binder通信，获取PMS，调用resolveIntent查找出合适Intent的应用信息
public ResolveInfo resolveIntent(Intent intent, String resolvedType,
int flags, int userId) {
// userID检测
if (!sUserManager.exists(userId)) return null;
// 权限检测
enforceCrossUserPermission(Binder.getCallingUid(), userId, false, false, "resolve intent");
// 全局包名查询意图匹配的应用信息
List<ResolveInfo> query = queryIntentActivities(intent, resolvedType, flags, userId);
return chooseBestActivity(intent, resolvedType, flags, query, userId);
}
resolveIntent中主要实现的逻辑如下：
- 检测UserManager是否存在当前的用户id
- 检测调用方法者是否拥有相应的权限
- 通过queryIntentActivities全局查找出合适的应用信息
- 通过chooseBestActivity进一步筛选出最合适的应用
queryIntentActivities全局查询合适intent
queryIntentActivities会根据传入的intent来选择查找方式，一种是没有包名，再系统所有的包中查找，否则查找安装包中指定的包。
public List<ResolveInfo> queryIntentActivities(Intent intent,
String resolvedType, int flags, int userId) {
if (!sUserManager.exists(userId)) return Collections.emptyList();
enforceCrossUserPermission(Binder.getCallingUid(), userId, false, false, "query intent activities");
ComponentName comp = intent.getComponent();
if (comp == null) {
if (intent.getSelector() != null) {
intent = intent.getSelector();
comp = intent.getComponent();
}
}
if (comp != null) {
final List<ResolveInfo> list = new ArrayList<ResolveInfo>(1);
final ActivityInfo ai = getActivityInfo(comp, flags, userId);
if (ai != null) {
final ResolveInfo ri = new ResolveInfo();
ri.activityInfo = ai;
list.add(ri);
}
return list;
}
// reader
synchronized (mPackages) {
final String pkgName = intent.getPackage();
// 包名信息为空，全局查找
if (pkgName == null) {
List<CrossProfileIntentFilter> matchingFilters =
getMatchingCrossProfileIntentFilters(intent, resolvedType, userId);
// Check for results that need to skip the current profile.
ResolveInfo xpResolveInfo = querySkipCurrentProfileIntents(matchingFilters, intent,
resolvedType, flags, userId);
if (xpResolveInfo != null && isUserEnabled(xpResolveInfo.targetUserId)) {
List<ResolveInfo> result = new ArrayList<ResolveInfo>(1);
result.add(xpResolveInfo);
return filterIfNotPrimaryUser(result, userId);
}
// Check for results in the current profile.
List<ResolveInfo> result = mActivities.queryIntent(
intent, resolvedType, flags, userId);
// Check for cross profile results.
xpResolveInfo = queryCrossProfileIntents(
matchingFilters, intent, resolvedType, flags, userId);
if (xpResolveInfo != null && isUserEnabled(xpResolveInfo.targetUserId)) {
result.add(xpResolveInfo);
// 排序
Collections.sort(result, mResolvePrioritySorter);
}
result = filterIfNotPrimaryUser(result, userId);
if (hasWebURI(intent)) {
CrossProfileDomainInfo xpDomainInfo = null;
final UserInfo parent = getProfileParent(userId);
if (parent != null) {
xpDomainInfo = getCrossProfileDomainPreferredLpr(intent, resolvedType,
flags, userId, parent.id);
}
if (xpDomainInfo != null) {
if (xpResolveInfo != null) {
// If we didn't remove it, the cross-profile ResolveInfo would be twice
// in the result.
result.remove(xpResolveInfo);
}
if (result.size() == 0) {
result.add(xpDomainInfo.resolveInfo);
return result;
}
} else if (result.size() <= 1) {
return result;
}
result = filterCandidatesWithDomainPreferredActivitiesLPr(intent, flags, result,
xpDomainInfo, userId);
Collections.sort(result, mResolvePrioritySorter);
}
return result;
}
// 根据包名查找
final PackageParser.Package pkg = mPackages.get(pkgName);
if (pkg != null) {
return filterIfNotPrimaryUser(
mActivities.queryIntentForPackage(
intent, resolvedType, flags, pkg.activities, userId),
userId);
}
return new ArrayList<ResolveInfo>();
}
}
chooseBestActivity筛选最合适的应用
对于前面传来的List
private ResolveInfo chooseBestActivity(Intent intent, String resolvedType,
int flags, List<ResolveInfo> query, int userId) {
if (query != null) {
final int N = query.size();
if (N == 1) {
// 只有一条，直接返回
return query.get(0);
} else if (N > 1) {
final boolean debug = ((intent.getFlags() & Intent.FLAG_DEBUG_LOG_RESOLUTION) != 0);
// If there is more than one activity with the same priority,
// then let the user decide between them.
ResolveInfo r0 = query.get(0);
ResolveInfo r1 = query.get(1);
if (DEBUG_INTENT_MATCHING || debug) {
Slog.v(TAG, r0.activityInfo.name + "=" + r0.priority + " vs "
+ r1.activityInfo.name + "=" + r1.priority);
}
// If the first activity has a higher priority, or a different
// default, then it is always desireable to pick it.
// 取前两条，选择优先级高的
if (r0.priority != r1.priority
|| r0.preferredOrder != r1.preferredOrder
|| r0.isDefault != r1.isDefault) {
return query.get(0);
}
// 已经设置过合适的主页应用，返回它
ResolveInfo ri = findPreferredActivity(intent, resolvedType,
flags, query, r0.priority, true, false, debug, userId);
if (ri != null) {
return ri;
}
ri = new ResolveInfo(mResolveInfo);
ri.activityInfo = new ActivityInfo(ri.activityInfo);
ri.activityInfo.applicationInfo = new ApplicationInfo(
ri.activityInfo.applicationInfo);
if (userId != 0) {
ri.activityInfo.applicationInfo.uid = UserHandle.getUid(userId,
UserHandle.getAppId(ri.activityInfo.applicationInfo.uid));
}
// Make sure that the resolver is displayable in car mode
if (ri.activityInfo.metaData == null) ri.activityInfo.metaData = new Bundle();
ri.activityInfo.metaData.putBoolean(Intent.METADATA_DOCK_HOME, true);
return ri;
}
}
return null;
}
筛选逻辑总结如下：
- 只存在一条信息，直接返回
- 存在两条以上，获取前两条，比较优先级高的返回
- 如果一样，查看之前用户是否设置过合适的主页，返回它
到此，超找到合适的主页应用信息，直接调用之前的mStackSupervisor.startHomeActivity便可以启动主页应用
小结
了解了主页应用的启动流程，可以方便我们入手定制系统信息的Launcher，一般实现用户自定的主页可以有以下几个实现方式：
- 修改应用层在Manifest.xml文件，设置优先级属性等，例如priority默认值为0，设置的值越大优先级越高
- framework可以仿照源码中工厂模式，在工厂模式检测前返回自己的主页应用
- 在chooseBestActivity代码的筛选中添加合适代码直接放回自己的主页应用
相关说明
在主页的启动流程中涉及到了安卓新手引导页的相关知识，具体可以参考一下博文
[请戳这里](https://github.com/Huoxubeiyin/SourceCode/blob/master/%E6%BA%90%E7%A0%81%E4%BF%AE%E6%94%B9%E4%B9%8B%E6%96%B0%E6%89%8B%E5%BC%95%E5%AF%BC.md)
