<h2>背景</h2>    <p>启动App内部的Activity，Android 6.0 系统</p>    <h2>概要</h2>    <ol>     <li>系统会为每个App创建一个进程，系统进程和App进程之间通过Binder通信</li>     <li>2个Binder接口 IActivityManager 和 IApplicationThread</li>     <li>几个Binder相关的类<br> ActivityManagerService extends ActivityManagerNative<br> ActivityManagerNative extends Binder implements IActivityManager<br> （简称AMS）<br> ApplicationThread extends ApplicationThreadNative<br> ApplicationThreadNative extends Binder implements IApplicationThread<br> （简称AT）</li>     <li>App进程通知AMS启动Activity-->进入系统进程处理，通知上一个Activity的AT进行pause-->进入App进程，pause完成后，通知AMS-->进入系统进程处理，通知App的AT进行scheduleLaunchActivity --> 进入App进程，创建Activity对象，调用Activity.onCreate()、onStart()、onResume()，通知AMS-->进入系统进程处理，通知上一个App的AT进行stop</li>    </ol>    <p><img src="https://simg.open-open.com/show/4c94f5f20807b28635e42e1387c8b2f9.png"></p>    <h2>详细</h2>    <p>----------App进程----------></p>    <p>1) Activity.startActivity()-->startActivityForResult()</p>    <pre>  <code class="language-java">public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {      ...      Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity(                  this, mMainThread.getApplicationThread(), mToken, this,                  intent, requestCode, options);   }</code></pre>    <p>注意第二个参数 mMainThread.getApplicationThread()</p>    <pre>  <code class="language-java">public final class ActivityThread {      final ApplicationThread mAppThread = new ApplicationThread();      public ApplicationThread getApplicationThread(){          return mAppThread;      }  }</code></pre>    <p>mMainThread就是ActivityThread，持续跟踪 mMainThread.mAppThread</p>    <p>2) Instrumentation.execStartActivity()</p>    <pre>  <code class="language-java">public ActivityResult execStartActivity(          Context who, IBinder contextThread, IBinder token, Activity target,          Intent intent, int requestCode, Bundle options) {      IApplicationThread whoThread = (IApplicationThread) contextThread;      ...      try {          ...          int result = ActivityManagerNative.getDefault()              .startActivity(whoThread, who.getBasePackageName(), intent,                      intent.resolveTypeIfNeeded(who.getContentResolver()),                      token, target != null ? target.mEmbeddedID : null,                      requestCode, 0, null, options);          ...      } catch (RemoteException e) {          throw new RuntimeException("Failure from system", e);      }      return null;  }</code></pre>    <p>继续跟踪 mMainThread.mAppThread，whoThread就是它</p>    <p>3) ActivityManagerNative.getDefault().startActivity()</p>    <pre>  <code class="language-java">public abstract class ActivityManagerNative extends Binder implements IActivityManager {      class ActivityManagerProxy implements IActivityManager      {          public ActivityManagerProxy(IBinder remote)          {              mRemote = remote;          }            public IBinder asBinder()          {              return mRemote;          }            public int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException {              ...              data.writeStrongBinder(caller != null ? caller.asBinder() : null);              ...              mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);              ...              return result;          }      }  }</code></pre>    <p><img src="https://simg.open-open.com/show/d9bc202610d2a52e65a6be8e0750383a.png"></p>    <p>继续跟踪 mMainThread.mAppThread，caller就是它，被传到 mRemote 的方法里了</p>    <p>App进程通知系统进程都是通过ActivityManagerNative</p>    <p>----------系统进程----------></p>    <p>4) ActivityManagerService.startActivity()</p>    <pre>  <code class="language-java">@Override  public final int startActivity(...) {      return startActivityAsUser(...);  }    @Override  public final int startActivityAsUser(...) {      ...      return mStackSupervisor.startActivityMayWait(...);  }</code></pre>    <p>5) ActivityStackSupervisor.startActivityMayWait()</p>    <p>加工将要启动的Activity的相关信息</p>    <p>6) ActivityStack.startPausingLocked()</p>    <p>在 launchActivity 之前先pause上一个Activity，prev.app 表明不仅限于当前APP</p>    <p><img src="https://simg.open-open.com/show/41e8fda16e8f5bb3ee530d68ae41a0d3.png"></p>    <p>7) ActivityStackSupervisor.realStartActivityLocked()</p>    <pre>  <code class="language-java">final boolean realStartActivityLocked(ActivityRecord r,          ProcessRecord app, boolean andResume, boolean checkConfig)          throws RemoteException {          ...          app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,                  System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),                  new Configuration(stack.mOverrideConfig), r.compat, r.launchedFromPackage,                  task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,                  newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);          ...      } catch (RemoteException e) {          ...          throw e;      }      ...      return true;  }</code></pre>    <p>上面跟踪App进程里的 mMainThread.mAppThread 那么久，终于在这里再现身影，app.thread 就是它的Binder接口</p>    <p>系统进程通知App进程都是通过ApplicationThreadNative</p>    <p>红框标示 ActivityManagerService.activityPaused() 说明App进程pause activity完成了</p>    <p><img src="https://simg.open-open.com/show/743c092fc25d933a532e45b06daa6a4f.png"></p>    <p>8) ApplicationThreadNative.scheduleLaunchActivity()</p>    <pre>  <code class="language-java">public abstract class ApplicationThreadNative extends Binder implements IApplicationThread {        class ApplicationThreadProxy implements IApplicationThread {          private final IBinder mRemote;            public final void scheduleLaunchActivity() throws RemoteException {              ...              mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null, IBinder.FLAG_ONEWAY);              ...          }      }    }</code></pre>    <p>----------App进程----------></p>    <p>9) ApplicationThreadNative</p>    <pre>  <code class="language-java">public abstract class ApplicationThreadNative extends Binder implements IApplicationThread {        @Override      public boolean onTransact(int code, Parcel data, Parcel reply, int flags)          throws RemoteException {              switch (code) {              ...              case SCHEDULE_PAUSE_ACTIVITY_TRANSACTION: {                  ...              }              case SCHEDULE_STOP_ACTIVITY_TRANSACTION: {                  ...              }              case SCHEDULE_RESUME_ACTIVITY_TRANSACTION: {                  ...              }              case SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION: {                  ...                  scheduleLaunchActivity(intent, b, ident, info, curConfig, overrideConfig, compatInfo,                  referrer, voiceInteractor, procState, state, persistentState, ri, pi,                  notResumed, isForward, profilerInfo);                  return true;              }              case SCHEDULE_NEW_INTENT_TRANSACTION: {                  ...              }              case SCHEDULE_FINISH_ACTIVITY_TRANSACTION: {                  ...              }              case SCHEDULE_CREATE_SERVICE_TRANSACTION: {                  ...              }              case SCHEDULE_BIND_SERVICE_TRANSACTION: {                  ...              }              case SCHEDULE_UNBIND_SERVICE_TRANSACTION: {                  ...              }              ...              return super.onTransact(code, data, reply, flags);          }      }  }</code></pre>    <p>10) ActivityThread.ApplicationThread.scheduleLaunchActivity()</p>    <pre>  <code class="language-java">public final class ActivityThread {      final ApplicationThread mAppThread = new ApplicationThread();      final H mH = new H();        private class ApplicationThread extends ApplicationThreadNative {          ...          public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,              ActivityInfo info, Configuration curConfig, Configuration overrideConfig,              CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,              int procState, Bundle state, PersistableBundle persistentState,              List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,              boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {              ...              sendMessage(H.LAUNCH_ACTIVITY, r);          }      }        private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {          Message msg = Message.obtain();          msg.what = what;          msg.obj = obj;          msg.arg1 = arg1;          msg.arg2 = arg2;          ...          mH.sendMessage(msg);      }  }</code></pre>    <p>mH是什么</p>    <p>11) ActivityThread.H</p>    <pre>  <code class="language-java">private class H extends Handler {      public static final int LAUNCH_ACTIVITY         = 100;      public static final int PAUSE_ACTIVITY          = 101;      public static final int PAUSE_ACTIVITY_FINISHING= 102;      public static final int STOP_ACTIVITY_SHOW      = 103;      public static final int STOP_ACTIVITY_HIDE      = 104;      public static final int SHOW_WINDOW             = 105;      public static final int HIDE_WINDOW             = 106;      public static final int RESUME_ACTIVITY         = 107;      public static final int SEND_RESULT             = 108;      public static final int DESTROY_ACTIVITY        = 109;      public static final int BIND_APPLICATION        = 110;      public static final int EXIT_APPLICATION        = 111;      public static final int NEW_INTENT              = 112;      public static final int RECEIVER                = 113;      public static final int CREATE_SERVICE          = 114;      public static final int SERVICE_ARGS            = 115;      public static final int STOP_SERVICE            = 116;        public static final int CONFIGURATION_CHANGED   = 118;      public static final int CLEAN_UP_CONTEXT        = 119;      public static final int GC_WHEN_IDLE            = 120;      public static final int BIND_SERVICE            = 121;      public static final int UNBIND_SERVICE          = 122;      public static final int DUMP_SERVICE            = 123;      public static final int LOW_MEMORY              = 124;      public static final int ACTIVITY_CONFIGURATION_CHANGED = 125;      public static final int RELAUNCH_ACTIVITY       = 126;      public static final int PROFILER_CONTROL        = 127;      public static final int CREATE_BACKUP_AGENT     = 128;      public static final int DESTROY_BACKUP_AGENT    = 129;      public static final int SUICIDE                 = 130;      public static final int REMOVE_PROVIDER         = 131;      public static final int ENABLE_JIT              = 132;      public static final int DISPATCH_PACKAGE_BROADCAST = 133;      public static final int SCHEDULE_CRASH          = 134;      public static final int DUMP_HEAP               = 135;      public static final int DUMP_ACTIVITY           = 136;      public static final int SLEEPING                = 137;      public static final int SET_CORE_SETTINGS       = 138;      public static final int UPDATE_PACKAGE_COMPATIBILITY_INFO = 139;      public static final int TRIM_MEMORY             = 140;      public static final int DUMP_PROVIDER           = 141;      public static final int UNSTABLE_PROVIDER_DIED  = 142;      public static final int REQUEST_ASSIST_CONTEXT_EXTRAS = 143;      public static final int TRANSLUCENT_CONVERSION_COMPLETE = 144;      public static final int INSTALL_PROVIDER        = 145;      public static final int ON_NEW_ACTIVITY_OPTIONS = 146;      public static final int CANCEL_VISIBLE_BEHIND = 147;      public static final int BACKGROUND_VISIBLE_BEHIND_CHANGED = 148;      public static final int ENTER_ANIMATION_COMPLETE = 149;        public void handleMessage(Message msg) {          switch (msg.what) {              case LAUNCH_ACTIVITY: {                  Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");                  final ActivityClientRecord r = (ActivityClientRecord) msg.obj;                  r.packageInfo = getPackageInfoNoCheck(                          r.activityInfo.applicationInfo, r.compatInfo);                  handleLaunchActivity(r, null);                  Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);              } break;              ...              case PAUSE_ACTIVITY:                  Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");                  handlePauseActivity((IBinder)msg.obj, false, (msg.arg1&1) != 0, msg.arg2,                          (msg.arg1&2) != 0);                  maybeSnapshot();                  Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                  break;              case RESUME_ACTIVITY:                  Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityResume");                  handleResumeActivity((IBinder) msg.obj, true, msg.arg1 != 0, true);                  Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                  break;                ...                ...          }      }   }</code></pre>    <p>看到这里，可以知道</p>    <p>管理Activity都是通过Handler.sendMessage()</p>    <p>要知道Handler都是和Looper配对使用的，新建Handler前，都需要初始化Looper，那Looper在哪</p>    <p>12) ActivityThread.main()</p>    <pre>  <code class="language-java">public static void main(String[] args) {      Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");      SamplingProfilerIntegration.start();        // CloseGuard defaults to true and can be quite spammy.  We      // disable it here, but selectively enable it later (via      // StrictMode) on debug builds, but using DropBox, not logs.      CloseGuard.setEnabled(false);        Environment.initForCurrentUser();        // Set the reporter for event logging in libcore      EventLogger.setReporter(new EventLoggingReporter());        AndroidKeyStoreProvider.install();        // Make sure TrustedCertificateStore looks in the right place for CA certificates      final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());      TrustedCertificateStore.setDefaultUserDirectory(configDir);        Process.setArgV0("<pre-initialized>");        Looper.prepareMainLooper();        ActivityThread thread = new ActivityThread();      thread.attach(false);        if (sMainThreadHandler == null) {          sMainThreadHandler = thread.getHandler();      }        if (false) {          Looper.myLooper().setMessageLogging(new                  LogPrinter(Log.DEBUG, "ActivityThread"));      }        // End of event ActivityThreadMain.      Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);      Looper.loop();        throw new RuntimeException("Main thread loop unexpectedly exited");  }</code></pre>    <p>重点是这三句</p>    <pre>  <code class="language-java">Looper.prepareMainLooper();  ActivityThread thread = new ActivityThread(); //内部 H mH = new H();  Looper.loop();</code></pre>    <p>如果不清楚Handler和Looper可以参考Handler和Looper解析</p>    <p>第一次启动App的时候，App还没有自己的进程，系统会创建一个新的进程，新的进程会导入android.app.ActivityThread，并且执行main()</p>    <p>main()方法里Looper.loop()死循环取消息（管理Activity、Service...的消息），其他线程传输消息到main线程都是通过ActivityThread.mH.sendMessage()</p>    <p>13) 回到 10) 里面的 sendMessage(H.LAUNCH_ACTIVITY, r)</p>    <p>--> 11) 里面的 handleLaunchActivity(r, null)</p>    <pre>  <code class="language-java">private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {      ...      WindowManagerGlobal.initialize();      ...      Activity a = performLaunchActivity(r, customIntent);      ...      handleResumeActivity(r.token, false, r.isForward,!r.activity.mFinished && !r.startsNotResumed);      ...  }     private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {      ...      Activity activity = null;      java.lang.ClassLoader cl = r.packageInfo.getClassLoader();      activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);//反射      ...      if (r.isPersistable()) {          mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);      } else {          mInstrumentation.callActivityOnCreate(activity, r.state);      }      ...      if (!r.activity.mFinished) {          activity.performStart();          r.stopped = false;      }      ...      return activity;  }</code></pre>    <p>mInstrumentation.callActivityOnCreate()-->activity.performCreate()-->onCreate()</p>    <p>handleLaunchActivity()内部先执行performLaunchActivity()再执行handleResumeActivity()</p>    <p>performLaunchActivity()内部会先执行mInstrumentation.callActivityOnCreate()再执行activity.performStart()</p>    <p>至此，Activity执行了onCreate()-->onStart()-->onResume()，在App内部启动完毕。</p>    <p>14) handleResumeActivity()</p>    <pre>  <code class="language-java">final void handleResumeActivity(IBinder token,          boolean clearHide, boolean isForward, boolean reallyResume) {      ...      ActivityClientRecord r = performResumeActivity(token, clearHide);      ...      try {          ActivityManagerNative.getDefault().activityResumed(token);      } catch (RemoteException ex) {      }      ...  }</code></pre>    <p>执行完onResume()通知AMS，系统进程就会接着去stop上一个Activity</p>    <h3>总结</h3>    <p>从上面的时序图也可以观察到</p>    <ol>     <li>Activity要通知系统进程，总是<br> Activity-->Instrumentation-->ActivityManagerNative--><br> 进入系统进程<br> ActivityManagerNative-->ActivityManagerService-->ActivityStackSupervisor/ActivityStack</li>     <li>系统进程要管理Activity，总是<br> ApplicationThreadNative--><br> 进入App进程<br> ApplicationThreadNative-->ActivityThread.ApplicationThread-->ActivityThread.H-->Instrumentation-->Activity</li>     <li>Activity A 启动 Activity B<br> 生命周期相关的整个过程是：a.onPause()-->b.onCreate()-->b.onStart()-->b.onResume()-->a.onStop()</li>    </ol>    <h3>如何debug SDK源码</h3>    <ol>     <li>使用模拟器，选Nexus系列</li>     <li>下载源码 <p><img src="https://simg.open-open.com/show/914d20245c3fa4ecda3c74d44b86790a.png"></p> </li>     <li>勾选Show all processes <p><img src="https://simg.open-open.com/show/28497c802fb0230913f1eb4211446bb2.png"></p> </li>     <li>选择system_process <p><img src="https://simg.open-open.com/show/d8dfb215d4238b4864472b912c47e19a.png"></p> </li>     <li>OK</li>    </ol>    <p> </p>    <p>来自：http://www.jianshu.com/p/d4cc363813a7</p>    <p> </p>