1、首先需要介绍init.rc脚本文件
该文件作为Android中LInux的第一个用户级进程init解析的，主要作用为文件系统初始化、设置环境变量、设置线程参数、装载等等。
开机后init.rc会首先装载class core以及class main的核心类（ServiceManager、SurfaceFlinger、Zygote、mediaServer）
2、开机动画的启动流程
（1）、在init.rc中有定义了bootanimation的进程服务，但是默认是disabled的
service bootanim /system/bin/bootanimation
class core
user graphics
group graphics audio
disabled
oneshot（2）、当init进程将SurfaceFlinger服务带起后，该服务会改变ctl.start系统变量，将其置为“bootanim”，以此来通知init进程启动应用程序bootanimation，从而开始启动开机动画
void SurfaceFlinger::init() {
...
...
...
startBootAnim();
}
void SurfaceFlinger::startBootAnim() {
// start boot animation
property_set("service.bootanim.exit", "0");
property_set("ctl.start", "bootanim");
}ps：SurfaceFlinger.cpp文件在\frameworks\native\services\surfaceflinger中，是一个.cpp文件
（3）、当系统进程将系统中的关键服务启动起来后，就会将程序启动器（Launcher）启动起来，进而通知停止显示动画
（4）、ActivityManagerService服务就会通知SurfaceFlingers服务来修改系统属性ctl.stop的值，从而通知init进程停止动画
3、加载Launcher的过程分析
（1）、开机启动后init进程会调用Zygote进程，Zygote进程会调用SystemServer进程从而调用其它的各种服务进程
（2）、在SystemServer中会启动ActivityManagerService并调用它的SystemReady()方法
（3）、在SystemReady()方法中会调用startHomeActivityLocked(mCurrentUserId, “systemReady”);方法
（4）、startActivityLocked()函数会调用getHomeIntent方法创建一个Intent，并给这个Intent设置CATEGORY_HOME类型
boolean startHomeActivityLocked(int userId, String reason) {
if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL
&& mTopAction == null) {
// We are running in factory test mode, but unable to find
// the factory test app, so just sit around displaying the
// error message and don't try to start anything.
return false;
}
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);
mStackSupervisor.startHomeActivity(intent, aInfo, reason);
}
}
return true;
}
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;
}（5）、将intent当做参数并调用resolveActivityInfo函数，这个函数主要用来调用PackageManagerService查询Category类型为home的activity，并返回一个activityinfo对象
private ActivityInfo resolveActivityInfo(Intent intent, int flags, int userId) {
ActivityInfo ai = null;
//ComponentName用来启动其它应用程序得到Activity或者Service
ComponentName comp = intent.getComponent();
try {
if (comp != null) {
// Factory test.
ai = AppGlobals.getPackageManager().getActivityInfo(comp, flags, userId);
} else {
ResolveInfo info = AppGlobals.getPackageManager().resolveIntent(
intent,
intent.resolveTypeIfNeeded(mContext.getContentResolver()),
flags, userId);
if (info != null) {
ai = info.activityInfo;
}
}
} catch (RemoteException e) {
// ignore
}
return ai;
}（6）、在resolveactivityinfo函数中会调用resolveIntent()函数，在这个函数中主要做了两件事，第一，检查权限，第二，查询符合要求的activities
@Override
public ResolveInfo resolveIntent(Intent intent, String resolvedType,
int flags, int userId) {
if (!sUserManager.exists(userId)) return null;
//检查权限
enforceCrossUserPermission(Binder.getCallingUid(), userId, false, false, "resolve intent");
//查询符合要求的activities,ActivityInfo是ResolveInfo的一个变量，这里返回的是符合条件的装有ResolveInfo的集合
List<ResolveInfo> query = queryIntentActivities(intent, resolvedType, flags, userId);
return chooseBestActivity(intent, resolvedType, flags, query, userId);
}（7）、queryIntentActivities方法用来查询所有符合条件的activities，并查询结果作为参数传入到chooseBestActivity()中进行比较
@Override
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();
}
}
//判断Intent指定的模块不为空，则返回list，满足条件的只有一个
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();
//如果没有指定报名，在系统所有包中查找
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);
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;
}
final PackageParser.Package pkg = mPackages.get(pkgName);
//如果Intent指定的包名不为空，则查找安装包中指定的包
if (pkg != null) {
return filterIfNotPrimaryUser(
mActivities.queryIntentForPackage(
intent, resolvedType, flags, pkg.activities, userId),
userId);
}
return new ArrayList<ResolveInfo>();
}
}（8）、调用chooseBestActivity()方法根据查询结果，选择一个最适合的activity，并返回ResolveInfo对象
/**
*选择并返回返回最合适的ResolveInfo
*/
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) {
return query.get(0);
} else if (N > 1) {
//如果合适的Activity大于1，并且想选择我们自己的应用程序作为默认启动Launcher
//添加代码返回返回我们需要启动的应用信息
//for(int i = 0;i < N;i ++){
// ResolveInfo ri = query.get(i);
// if(ri.activityinfo.packageName.equals("包名"){
// return ri;
// }
//}
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.
//如果符合条件的activity大于1，则只选出前两个，进行比较进而选出优先级最高的
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.
if (r0.priority != r1.priority
|| r0.preferredOrder != r1.preferredOrder
|| r0.isDefault != r1.isDefault) {
return query.get(0);
}
// If we have saved a preference for a preferred activity for
// this Intent, use that.
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;
}
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