一、概念
Android10（API29）开始，ActivityTaskManagerService 接管 ActivityManagerService。
二、启动ATMS过程
三、启动APP & 跳转Activity过程
- 调用 Activity 的 startActivity 方法来启动目标 Activity
- 接着就会调用到 Instrunmentation 的 execStartActivity 方法，通过获取 ATMS 的 binder 代理对象，然后调用到 ATMS 的 startActivity 中去
- 调用到 ATMS 中后，会执行到
ActivityStarter的 execute 方法，内部最终执行到了 executeRequest ，接着就会进行一些校验和判断权限，包括进程检查，intent检查，权限检查等，后面就会创建ActivityRecord，用来保存 Activity 的相关信息， - 然后就会根据启动模式计算 flag ，设置启动 Activity 的 Task 栈。
- 在 ActivityTaskSupervisor 中检查要启动的 Activity 进程是否存在，存在则向客户端进程 ApplicationThread 回调启动 Activity，否则就创建进程。
- 会调到 ActivityThread 后在 TransactionExecute 中开始执行system_server回调回来的事务，处理各种回调，切换到对应的生命周期
- 最后又回调到 ActivityThread 的 handleLaunchActivity 来启动 Activity。在其中调用了 performLaunchActivity 方法。
- 在 performLaunchActivity 中通过反射创建 Activity 实例，如果没有 Application 则先进行创建，然后再调用Activity 的 attach 方法进行初始化，最后回调 activity 的 onCreate 方法。
3.1 Activity → ATMS
启动一个 APP 或跳转一个 Activity 都是调用的 startActivity()，进而调用 startActivityForResult()。
3.1.1 Activity
Activity{
public void startActivity(Intent intent, @Nullable Bundle options) {
startActivityForResult(intent, -1, options);
}
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
//委托给Instrumentation来启动
Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity(this, mMainThread.getApplicationThread(), mToken, this, intent, requestCode, options);
mMainThread.sendActivityResult(mToken, mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData());
}
}3.1.2 Instrumentation
Instrumentation{
//形参who：用来启动Activity的对象
//形参contextThread：Binder对象，具有跨进程通信的能力，传入的是mMainThread.getApplicationThread()
//形参token：Binder对象，指向了服务端一个 ActivityRecord 对象
//形参target：当前Activity
public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, String target, Intent intent, int requestCode, Bundle options) {
//获取一个Binder对象，转为AIDL所属类型（ATMS的proxy），然后调用ATMS的startActivity()进行跨进程通信
int result = ActivityTaskManager.getService().startActivity(whoThread,
who.getOpPackageName(), who.getAttributionTag(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()), token, target,
requestCode, 0, null, options);
//判断能否启动Activity，不能启动就会抛出异常，例如activity未在manifest中声明等。
checkStartActivityResult(result, intent);
}
}ActivityTaskManager{
public static IActivityTaskManager getService() {
return IActivityTaskManagerSingleton.get();
}
//一种单例模式
private static final Singleton<IActivityTaskManager> IActivityTaskManagerSingleton = new Singleton<IActivityTaskManager>() {
@Override
protected IActivityTaskManager create() {
//获取ATMS的代理对象Binder
final IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);
return IActivityTaskManager.Stub.asInterface(b);
}
};
}3.2 ATMS → PMS
ActivityTaskManagerService{
public final int startActivity(IApplicationThread caller, String callingPackage, String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, UserHandle.getCallingUserId());
}
private int startActivityAsUser(IApplicationThread caller, String callingPackage, @Nullable String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
//获取ActivityStarter实例，去执行execute方法
return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
...
.execute();
}
}ActivityStarter{
int execute() {
if (mRequest.activityInfo == null) {
mRequest.resolveActivity(mSupervisor);
}
}
static class Request {
void resolveActivity(ActivityTaskSupervisor supervisor) {
//AndroidManifest中intent标签
resolveInfo = supervisor.resolveIntent(intent, resolvedType, userId, 0, computeResolveFilterUid(callingUid, realCallingUid, filterCallingUid));
//转为Activity标签
activityInfo = supervisor.resolveActivity(intent, resolveInfo, startFlags, profilerInfo);
}
}
}
ActivityTaskSupervisor{
ResolveInfo resolveIntent(Intent intent, String resolvedType, int userId, int flags, int filterCallingUid) {
//通过ATMS获取抽象类PackageManagerInternal
//PMS内部类PackageManagerInternalImpl实现了它（内部类持有外部类，就可以调用PMS的方法了）
//resolveIntent()会将从PMS的mPackages中查询到的ActivityInfo赋值给ResultInfo
mService.getPackageManagerInternalLocked().resolveIntent(intent, resolvedType, modifiedFlags, privateResolveFlags, userId, true, filterCallingUid);
}
//将获取的ResultInfo转为ActivityInfo
ActivityInfo resolveActivity(Intent intent, String resolvedType, int startFlags, ProfilerInfo profilerInfo, int userId, int filterCallingUid) {
final ResolveInfo rInfo = resolveIntent(intent, resolvedType, userId, 0, filterCallingUid);
return resolveActivity(intent, rInfo, startFlags, profilerInfo);
}
}