1. Activity启动
Activity是一个比较好的模板方法模式。在Android系统启动时，第一个启动的进程是zygote进程，然后由zygote启动SystemServer，再后就是启动AWS、WMS等系统核心服务，这些服务承载着整个Android系统与客户端程序交互。zygote除了启动系统服务与进程之外，普通的用户进程也是由zygote进程fork而来，当一个进程启动起来后，就会加载用户在AndroidManifest.xml中配置的默认加载的Activity，此时加载的入口是ActivityThread.main方法，是整个程序的入口。
main方法主要功能就是创建Application和Activity，并且调用Activity的生命周期函数。
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| public static void (String[] args) {
SamplingProfilerIntegration.start();
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
EventLogger.setReporter(new EventLoggingReporter());
Security.addProvider(new AndroidKeyStoreProvider());
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();
}
Looper.loop();
}
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
...
android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
}
}
}
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上述程序可以看到，在ActivityThread.main中主要的功能就是创建了UI线程消息循环，并启动循环消息循环。最重要的是创建了ActivityThread并调用了attach方法。在方法中又调用了AWS中的attachApplication方法。我们先看看ApplicationThread是什么
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| private class ApplicationThread extends ApplicationThreadNative {
public final void scheduleResumeActivity(IBinder token, int processState,
boolean isForward, Bundle resumeArgs) {
sendMessage(H.RESUME_ACTIVITY, token, isForward ? 1 : 0);
}
public final void scheduleLaunchActivity(...) {
updateProcessState(procState, false);
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info
r.state = state;
updatePendingConfiguration(curConfig);
...
sendMessage(H.LAUNCH_ACTIVITY, r);
}
}
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ApplicationThread通过handler管理Activity的生命周期。继续关注AWS中的attachApplication方法
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| public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
ProcessRecord app;
try {
...
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMod 大专栏 Activity源码解析 - 读书笔记e, enableOpenGlTrace,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
updateLruProcessLocked(app, false, null);
app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
} catch (Exception e) {
return false;
}
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
}
}
return true;
}
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忽略些代码，这里关注mStackSupervisor.attachApplicationLocked(app)。
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| boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFrontStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked(null);
if (hr != null) {
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
if (realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (RemoteException e) {
}
}
}
}
}
return didSomething;
}
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这里会遍历整个Activity栈并且找出栈顶的ActivityStack，然后调用realStartActivityLocked来真正启动 Activity
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| final boolean realStartActivityLocked(ActivityRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig)
throws RemoteException {
final ActivityStack stack = r.task.stack;
try {
mService.ensurePackageDexOpt(r.intent.getComponent().getPackageName());
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_TOP);
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
r.compat, r.launchedFromPackage, r.task.voiceInteractor, app.repProcState,
r.icicle, r.persistentState, results, newIntents, !andResume,
mService.isNextTransitionForward(), profilerInfo);
} catch (RemoteException e) {}
return true;
}
|
ActivityThread的内部类ApplicationThread的scheduleLaunchActivity方法。之后会调ActivityThread的handleLaunchActivity函数，再调用performLaunchActivity来创建Activity，并将Activity和Application关联上。然后调用onCreate方法。
2. setContentView
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| public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
public void setContentView(int layoutResID) {
if (mContentParent == null) {
installDecor();
}
mLayoutInflater.inflate(layoutResID, mContentParent);
}
private void installDecor() {
if (mDecor == null) {
mDecor = return new DecorView(getContext(), -1);
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
}
}
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setContentView基本流程
- 构建mDecor对象
- 设置窗口属性
- inflate布局