解析Android应用启动流程-优快云博客

Activity启动分为很多种情况，这里说的是打开新的应用程序第一个Activity的流程。

1. AcitivityManager产生新进程，新进程从android.app.ActivityThread.main开始运行。这里就是一般意义上的程序入口点，类似于C的main函数。

ActivityManagerService.java

private final void startProcessLocked(ProcessRecord app, String hostingType, String hostingNameStr) {

// Process里面通知Zygote服务，Zygote真正产生新的进程（准确说是复制一个）

int pid = Process.start("android.app.ActivityThread",
mSimpleProcessManagement ? app.processName : null, uid, uid,

}

2.ActivityThread的main函数中将Looper准备起来，prepareMainLooper标志着这是应用程序主线程的Looper对象。

ActivityThread.java

public static final void main(String[] args) {

Looper.prepareMainLooper();

ActivityThread thread = new ActivityThread();
thread.attach(false);
// 这里闭合消息循环
Looper.loop();

}

3. 接下来调用attach，参数为false，表明这不是系统进程，是给普通应用程序用使用的进程。

ActivityThread.java

private final void attach(boolean system) {

ViewRoot.addFirstDrawHandler(new Runnable() {
public void run() {
ensureJitEnabled();
}
});
RuntimeInit.setApplicationObject(mAppThread.asBinder());
IActivityManager mgr = ActivityManagerNative.getDefault();
mgr.attachApplication(mAppThread);

}

mAppThread是ApplicationThread对象，是提供给ActivityManagerService控制ActivityThread的回调接口。

private final class ApplicationThread extends ApplicationThreadNative {

public final void schedulePauseActivity(IBinder token, boolean finished,boolean userLeaving, int configChanges){

queueOrSendMessage(finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
token, (userLeaving ? 1 : 0), configChanges);
}

public final void scheduleStopActivity(IBinder token, boolean showWindow, int configChanges) {
queueOrSendMessage(showWindow ? H.STOP_ACTIVITY_SHOW : H.STOP_ACTIVITY_HIDE,
token, 0, configChanges);
}

.........

}

ActivityManagerService要Pause当前Activity，就会调用schedulePauseActivity想本地的消息循环中加入一个H.PAUSE_ACTIVITY的消息，然后立即返回以避免ActivityManagerService的阻塞。

4.现在又回到了ActivityManagerService中

ActivityManagerService.java

// ActivityManagerService中XXXLocked函数才是真正干活的地方，XXX只是个套

public final void attachApplication(IApplicationThread thread) {
int callingPid = Binder.getCallingPid();
attachApplicationLocked(thread, callingPid);
}

private final boolean attachApplicationLocked(IApplicationThread thread, int pid) {

// 这里取出对应该Pid的ProcessRecord对象，如果取不出来，你就等着out吧

app = mPidsSelfLocked.get(pid)

// 为ProcessRecord对象补充信息

app.thread = thread;
app.curAdj = app.setAdj = -100;
app.curSchedGroup = Process.THREAD_GROUP_DEFAULT;
app.setSchedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
app.forcingToForeground = null;
app.foregroundServices = false;
app.debugging = false;
// 清除timeout监测
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);

// 回调之前的ActivityThread，让它记住自己在ActivityManagerService中的相关信息，传这么大坨东西，真给力

thread.bindApplication(processName, app.instrumentationInfo != null
? app.instrumentationInfo : app.info, providers,
app.instrumentationClass, app.instrumentationProfileFile,
app.instrumentationArguments, app.instrumentationWatcher, testMode,
isRestrictedBackupMode || !normalMode,
mConfiguration, getCommonServicesLocked());

// topRunningActivityLocked的意思没看太明白

HistoryRecord hr = topRunningActivityLocked(null);

// 启动Activity

realStartActivityLocked(hr, app, true, true);

}

private final boolean realStartActivityLocked(HistoryRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig){

// 这里又跑到ActivityThread中去了

app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
System.identityHashCode(r),
r.info, r.icicle, results, newIntents, !andResume,
isNextTransitionForward());

}

5.ActivityThread开始调度用户的Activity启动了

ActivityThread.java

private final void handleLaunchActivity(ActivityRecord r, Intent customIntent) {

}