Activity建立流程
這次從Activity的handleLaunchActivity(...)方法開始分析，因為前面的流程已經在建立Application過程中講過了。 從程式碼中我們可以看出Activity是通過performLauncherActivity(...)方法建立的。我們看下這個方法幹了啥
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;
}
複製程式碼從程式碼中我們可以看出:
- 首先建立了ContextImpl，然後通過Intrumentation的newActivity(...)來建立Activity的例項。
- 然後通過Intrumentation的callActivityOnCreate(...)來呼叫Activity的onCreate()方法
- 通過activity.performStart(...)來呼叫Activity的onStart()方法
- 如果上次Activity被異常殺死，則通過Intrumentation的callActivityOnRestoreInstanceState(...)來執行Activity的performRestoreInstanceState(...)方法
- 執行完成後則返回Activity例項並回到handleLaunchActivity(...)方法中，通過handleResumeActivity(...)方法來呼叫Activity的onResume方法。 以上就是Activity的建立流程.
Service建立流程
AMS完成AMS程式中的Service建立後，通過ApplitionThread的scheduleCreateService(...)方法來通過ActivityThread來建立Client端的Service。下面我們看下scheduleCreateService(...)的原始碼
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);
}
複製程式碼scheduleCreateService(...)方法會傳送CREATE_SERVICE給UI執行緒，下面看看UI執行緒的針對這個Message幹了什麼
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;
...
}
}
複製程式碼UI執行緒收到CREATE_SERVICE這個message後呼叫了handleCreateService(...)方法，接著看下handleCreateService(...)幹了什麼
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);
}
}
}
複製程式碼從原始碼中我們可以看出，首先通過ClassLoader來建立Service的例項。然後建立ContextImpl來讓Service attach，由此可以證明，Service對應的mBase也為ContextImpl，然後直接呼叫Service的onCreate()。