Activity创建流程
这次从Activity的handleLaunchActivity(...)方法开始分析，因为前面的流程已经在创建Application过程中讲过了。 从代码中我们可以看出Activity是通过performLauncherActivity(...)方法创建的。我们看下这个方法干了啥
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { ... ContextImpl appContext = createBaseContextForActivity(r); Activity activity = null; try { java.lang.ClassLoader cl = appContext.getClassLoader(); activity = mInstrumentation.newActivity( cl, component.getClassName(), r.intent); StrictMode.incrementExpectedActivityCount(activity.getClass()); r.intent.setExtrasClassLoader(cl); r.intent.prepareToEnterProcess(); if (r.state != null) { r.state.setClassLoader(cl); } } catch (Exception e) { if (!mInstrumentation.onException(activity, e)) { throw new RuntimeException( "Unable to instantiate activity " + component+ ": " + e.toString(), e); } } ... if (r.isPersistable()) { mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnCreate(activity, r.state); } if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onCreate()"); } r.activity = activity; r.stopped = true; if (!r.activity.mFinished) { activity.performStart(); r.stopped = false; } if (!r.activity.mFinished) { if (r.isPersistable()) { if (r.state != null || r.persistentState != null) { mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state, r.persistentState); } } else if (r.state != null) { mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state); } } ... return activity; }复制代码 从代码中我们可以看出:
- 首先创建了ContextImpl，然后通过Intrumentation的newActivity(...)来创建Activity的实例。
- 然后通过Intrumentation的callActivityOnCreate(...)来调用Activity的onCreate()方法
- 通过activity.performStart(...)来调用Activity的onStart()方法
- 如果上次Activity被异常杀死，则通过Intrumentation的callActivityOnRestoreInstanceState(...)来执行Activity的performRestoreInstanceState(...)方法
- 执行完成后则返回Activity实例并回到handleLaunchActivity(...)方法中，通过handleResumeActivity(...)方法来调用Activity的onResume方法。 以上就是Activity的创建流程.
Service创建流程
AMS完成AMS进程中的Service创建后，通过ApplitionThread的scheduleCreateService(...)方法来通过ActivityThread来创建Client端的Service。下面我们看下scheduleCreateService(...)的源码
public final void scheduleCreateService(IBinder token, ServiceInfo info, CompatibilityInfo compatInfo, int processState) { updateProcessState(processState, false); CreateServiceData s = new CreateServiceData(); s.token = token; s.info = info; s.compatInfo = compatInfo; sendMessage(H.CREATE_SERVICE, s); }复制代码 scheduleCreateService(...)方法会发送CREATE_SERVICE给UI线程，下面看看UI线程的针对这个Message干了什么
public void handleMessage(Message msg) { if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what)); switch (msg.what) { ... case CREATE_SERVICE: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceCreate: " + String.valueOf(msg.obj))); handleCreateService((CreateServiceData)msg.obj); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; ... } }复制代码 UI线程收到CREATE_SERVICE这个message后调用了handleCreateService(...)方法，接着看下handleCreateService(...)干了什么
private void handleCreateService(CreateServiceData data) { ... LoadedApk loadedApk = getLoadedApkNoCheck( data.info.applicationInfo, data.compatInfo); Service service = null; try { java.lang.ClassLoader cl = loadedApk.getClassLoader(); service = (Service) cl.loadClass(data.info.name).newInstance(); } catch (Exception e) { if (!mInstrumentation.onException(service, e)) { throw new RuntimeException( "Unable to instantiate service " + data.info.name + ": " + e.toString(), e); } } try { if (localLOGV) Slog.v(TAG, "Creating service " + data.info.name); ContextImpl context = ContextImpl.createAppContext(this, loadedApk); context.setOuterContext(service); Application app = loadedApk.makeApplication(false, mInstrumentation); service.attach(context, this, data.info.name, data.token, app, ActivityManager.getService()); service.onCreate(); mServices.put(data.token, service); try { ActivityManager.getService().serviceDoneExecuting( data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); } } catch (Exception e) { if (!mInstrumentation.onException(service, e)) { throw new RuntimeException( "Unable to create service " + data.info.name + ": " + e.toString(), e); } } }复制代码 从源码中我们可以看出，首先通过ClassLoader来创建Service的实例。然后创建ContextImpl来让Service attach，由此可以证明，Service对应的mBase也为ContextImpl，然后直接调用Service的onCreate()。