ActivityThread.main
我们知道app的启动是从ActivityThread.main方法开始的，所以我们先从main看起
public static void main(String[] args) {
...
//创建Looper
Looper.prepareMainLooper();
//创建ActivityThread
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
...
//开启Looper循环
Looper.loop();
...
}
main方法里主要做了三件事
- 创建主线程Looper,并开启循环
- 创建ActivityThread
- 调用
attach方法
ActivityThread.attach
接下来我们看ActivityThread.attach方法
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
...
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
...
}
...
}
...
}
attach方法里主要做里就是调用ActivityManager.getService() 方法返回IActivityManager 类型的 Binder 对象, 具体实现是在AMS里实现attachApplication
ActivityManagerService.attachApplication
public final void attachApplication(IApplicationThread thread) {
...
attachApplicationLocked(thread, callingPid);
...
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
....
thread.bindApplication(processName, appInfo, providers,
app.instr.mClass,
profilerInfo, app.instr.mArguments,
app.instr.mWatcher,
app.instr.mUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial);
...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
...
}
}
...
}
可以发现attachApplication实际调用了attachApplicationLocked,而在attachApplicationLocked里又通过IApplicationThread (其类型是ApplicationThread是ActivityThread的内部类，继承自IApplicationThread.Stub) 的bindApplication方法
ActivityThread.bindApplication
public final void bindApplication(String processName, ApplicationInfo appInfo,
List providers, ComponentName instrumentationName,
ProfilerInfo profilerInfo, Bundle instrumentationArgs,
IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection, int debugMode,
boolean enableBinderTracking, boolean trackAllocation,
boolean isRestrictedBackupMode, boolean persistent, Configuration config,
CompatibilityInfo compatInfo, Map services, Bundle coreSettings,
String buildSerial) {
...
sendMessage(H.BIND_APPLICATION, data);
}
private void sendMessage(int what, Object obj) {
sendMessage(what, obj, 0, 0, false);
}
private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
if (DEBUG_MESSAGES) Slog.v(
TAG, "SCHEDULE " + what + " " + mH.codeToString(what)
+ ": " + arg1 + " / " + obj);
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
if (async) {
msg.setAsynchronous(true);
}
mH.sendMessage(msg);
}
bindApplication最终调用了mH.sendMessage方法，因为AMS通过ApplicationThread回调到我们的进程，这也是一次跨进程过程，而ApplicationThread就是一个binder，回调逻辑是在binder线程池中完成的，所以需要通过Handler 将其切换到ui线程.所以这里调用mh.sendMessage(mh是ActivityThread 的内部类 H 的一个实例)来通知处理BIND_APPLICATION事件
H.handleMessage
public void handleMessage(Message msg) {
...
switch (msg.what) {
...
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
...
}
}
可以看到Handler.H收到BIND_APPLICATION事件后实际调用来handleBindApplication方法来完成Application的创建以及ContentProvider的创建
ActivityThread.handleBindApplication
private void handleBindApplication(AppBindData data) {
....
final InstrumentationInfo ii;
....
if (ii != null) {
//1.创建ContentImpl
final ContextImpl instrContext = ContextImpl.createAppContext(this, pi);
try {
final ClassLoader cl = instrContext.getClassLoader();
mInstrumentation = (Instrumentation)
cl.loadClass(data.instrumentationName.getClassName()).newInstance();
} catch (Exception e) {
throw new RuntimeException(
"Unable to instantiate instrumentation "
+ data.instrumentationName + ": " + e.toString(), e);
}
//2.创建Instrumentation
final ComponentName component = new ComponentName(ii.packageName, ii.name);
mInstrumentation.init(this, instrContext, appContext, component,
data.instrumentationWatcher, data.instrumentationUiAutomationConnection);
....
//3.创建Application对象
Application app;
app = data.info.makeApplication(data.restrictedBackupMode, null);
// Propagate autofill compat state
app.setAutofillCompatibilityEnabled(data.autofillCompatibilityEnabled);
mInitialApplication = app;
...
//4.启动当前进程中的ContentProvider和调用其onCreate方法
if (!data.restrictedBackupMode) {
if (!ArrayUtils.isEmpty(data.providers)) {
installContentProviders(app, data.providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
//5.调用Application的onCreate方法
try {
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
}
}
- 3.1
LoadedApk.makeApplicationApplication的创建
public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
...
Application app = null;
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals("android")) {
initializeJavaContextClassLoader();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} catch (Exception e) {
if (!mActivityThread.mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to instantiate application " + appClass
+ ": " + e.toString(), e);
}
}
mActivityThread.mAllApplications.add(app);
mApplication = app;
if (instrumentation != null) {
try {
instrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!instrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
}
...
return app;
}
- 3.1.1
Instrumentation.newApplication
public Application newApplication(ClassLoader cl, String className, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
Application app = getFactory(context.getPackageName())
.instantiateApplication(cl, className);
app.attach(context);
return app;
}
AppComponentFactory.instantiateApplication
public @NonNull Application instantiateApplication(@NonNull ClassLoader cl,
@NonNull String className)
throws InstantiationException, IllegalAccessException, ClassNotFoundException {
return (Application) cl.loadClass(className).newInstance();
}
经过 上面的5个步骤就完成了Application的创建和启动，可以看到在第5步调用Application的onCreate方法之前，第4步进行了ContentProvicer的创建和调用其onCreate,这里就解释到了为什么可以在ContentProvicer.onCreate里初始化sdk,下面介绍下ContentProvicer的创建和调用其onCreate
- 4.1
ActivityThread.installContentProviders
private void installContentProviders(
Context context, List providers) {
final ArrayList results = new ArrayList<>();
for (ProviderInfo cpi : providers) {
ContentProviderHolder cph = installProvider(context, null, cpi,
false /*noisy*/, true /*noReleaseNeeded*/, true /*stable*/);
if (cph != null) {
cph.noReleaseNeeded = true;
results.add(cph);
}
}
try {
ActivityManager.getService().publishContentProviders(
getApplicationThread(), results);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
installContentProviders完成了ContentProvider的启动，它首先遍历当前进程的ProviderInfo列表并一一调用其installProvder方法来启动它，接着将已启动的ContentProvider发布到AMS上，AMS会把它们存在ProviderMap里，这样外部调用者就可以直接从AMS中获取到ContentProvider
- 4.1.1
ActivityThread.installProvider
private ContentProviderHolder installProvider(Context context,
ContentProviderHolder holder, ProviderInfo info,
boolean noisy, boolean noReleaseNeeded, boolean stable) {
....
final java.lang.ClassLoader cl = c.getClassLoader();
LoadedApk packageInfo = peekPackageInfo(ai.packageName, true);
if (packageInfo == null) {
packageInfo = getSystemContext().mPackageInfo;
}
localProvider = packageInfo.getAppFactory()
.instantiateProvider(cl, info.name);
provider = localProvider.getIContentProvider();
if (provider == null) {
Slog.e(TAG, "Failed to instantiate class " +
info.name + " from sourceDir " +
info.applicationInfo.sourceDir);
return null;
}
localProvider.attachInfo(c, info);
....
}
这里通过类加载器完成了ContentProvider的创建
- 4.1.1.1
ContentProvider.attachInfo
private void attachInfo(Context context, ProviderInfo info, boolean testing) {
mNoPerms = testing;
/*
* Only allow it to be set once, so after the content service gives
* this to us clients can't change it.
*/
if (mContext == null) {
mContext = context;
if (context != null) {
mTransport.mAppOpsManager = (AppOpsManager) context.getSystemService(
Context.APP_OPS_SERVICE);
}
mMyUid = Process.myUid();
if (info != null) {
setReadPermission(info.readPermission);
setWritePermission(info.writePermission);
setPathPermissions(info.pathPermissions);
mExported = info.exported;
mSingleUser = (info.flags & ProviderInfo.FLAG_SINGLE_USER) != 0;
setAuthorities(info.authority);
}
ContentProvider.this.onCreate();
}
}
在installProvider方法里除了完成了ContentProvider的创建还掉用了attachInfo,在改方法里来调用它的onCreate方法。到此位置ContentProvider的创建已经完成，并且它的onCreate也被调用