源码基于API 26
startActivity()上车
@Override
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}复制代码没什么好说的
//启动一个activity不需要返回值
//如果context之外调用startActivity(),需要给intent添加{@link Intent#FLAG_ACTIVITY_NEW_TASK}
//@param options 附加的选项指示如果启动activity
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
//可重写该方法兼容应用需求
startActivityForResult(intent, -1);
}
}复制代码可重写该方法，参考FragmentActivity
//If requestCode >= 0, this code will be returned in onActivityResult() when the activity exits.
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {
startActivityForResult(intent, requestCode, null);
}复制代码最终执行该方法
//启动一个activity在finish()会返回一个结果在onActivityResult()中
//如果在onCreate()/onResume()方法中调用该方法，window不显示界面直到该方法返回结果
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options) {
//父activity一般为空
if (mParent == null) {
//通过ActivityOptions帮助类生成一个bundle，指示该如何启动该activity
options = transferSpringboardActivityOptions(options);
//Instrumentation基类启动Activity
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
//返回结果
if (ar != null) {
//最终会执行Activity的onActivityResult()
mMainThread.sendActivityResult(
mToken, mEmbeddedID, requestCode, ar.getResultCode(),
ar.getResultData());
}
if (requestCode >= 0) {
//当接收到返回的结果了启动的activity才会显示
mStartedActivity = true;
}
//取消输入并开始activity退出动画
cancelInputsAndStartExitTransition(options);
} else {
//不考虑mParent不为null的情况，远古级方法，不采用了
if (options != null) {
mParent.startActivityFromChild(this, intent, requestCode, options);
} else {
mParent.startActivityFromChild(this, intent, requestCode);
}
}
}复制代码执行Instrumentation的execStartActivity()，Instrumentation起着监控系统和应用的作用
//target:源activity
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
//获取当前内容索引，不重写onProvideReferrer()返回null
Uri referrer = target != null ? target.onProvideReferrer() : null;
if (referrer != null) {
//不为null添加至intent
intent.putExtra(Intent.EXTRA_REFERRER, referrer);
}
//activity监视器
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
if (am.match(who, null, intent)) {
am.mHits++;
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
//内容是否有迁移
intent.migrateExtraStreamToClipData();
//准备intent并离开当前进程
intent.prepareToLeaveProcess(who);
//本地activityManager启动activity
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
//检查启动activity返回结果,抛出异常
checkStartActivityResult(result, intent);
//跨进程异常
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}复制代码ActivityManagerNative.getDefault()获取IActivityManager接口,调用startActivity()方法。
事实上是ServiceManager.getService("activity"), 即获取ActivityManagerService(AMS)并通过Binder远程调用ActivityManagerService类的startActivity()方法。
private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
protected IActivityManager create() {
//获取activityService
IBinder b = ServiceManager.getService("activity");
if (false) {
Log.v("ActivityManager", "default service binder = " + b);
}
//返回service代理对象
IActivityManager am = asInterface(b);
if (false) {
Log.v("ActivityManager", "default service = " + am);
}
return am;
}
};
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
//通过binder获取AMS
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
//代理obj其实就是AMS
return new ActivityManagerProxy(obj);
}复制代码IAvityManager对所有运行着的Activity交互提供了接口，ActivityMangerNative实现了IActivityManager接口，IActivityManger的大多数功能都是调用了ActivityManagerNative类接口来完成的，而AMS继承了ActivityMangerNative。
ActivityMangerNative作为IActivityManger和AMS的中间类，解耦了两者间的依赖，所有对AMS的访问都转换成了对ActivityMangerNative的代理类ActivityMangerProxy的访问。
从这里的getDefault().startActivity()开始从本应用通过binder跨进程调用AMS的方法
@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
@Override
public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {
enforceNotIsolatedCaller("startActivity");
userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
userId, false, ALLOW_FULL_ONLY, "startActivity", null);
// TODO: Switch to user app stacks here.
return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, bOptions, false, userId, null, null);
}复制代码ActivityStarter类负责处理启动activity之前的准备工作，包括Activity的Intent和Flags的逻辑, 还有管理Stack和TaskRecord.
ActivityStarter类的调用流程:
- ActivityStarter#startActivityMayWait(根据Intent获取Activity的启动信息(ResolveInfo和ActivityInfo)
- ActivityStarter#startActivityLocked(创建ActivityRecord, 含有Activity的核心信息)
- ActivityStarter#startActivityUnchecked(根据启动的Flag信息, 设置TaskRecord)
接着执行ActivityStackSupervisor类的resumeFocusedStackTopActivityLocked()方法
boolean resumeFocusedStackTopActivityLocked(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
if (targetStack != null && isFocusedStack(targetStack)) {
return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
if (r == null || r.state != RESUMED) {
mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
}
return false;
}复制代码ActivityStackSupervisor类与ActivityStack类配合使用. ActivityStackSupervisor负责管理Task和Stack, 而ActivityStack负责管理在Stack和Task中的Activity
ActivityStackSupervisor类与ActivityStack类的调用流程:
- ActivityStackSupervisor#resumeFocusedStackTopActivityLocked
- ActivityStack#resumeTopActivityUncheckedLocked
- ActivityStack#resumeTopActivityInnerLocked(根据ActivityRecord和ActivityOptions完成Activity的切换, 移至栈顶)
- ActivityStackSupervisor#startSpecificActivityLocked
ActivityStackSupervisor#realStartActivityLocked(真正启动activity)
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException { ... app.forceProcessStateUpTo(mService.mTopProcessState); app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken, System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration), new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results, newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo); ... }复制代码最后由ActivityThread中的ApplicationThread调用scheduleLaunchActivity完成Activity的真正启动。
这里的thread是IApplicationThread接口，该接口继承了IInterface接口，实现方法asBinder()方法作为binder通信。这里通过binder跨进程由系统进程调用应用进程启动activity