android 8.0源码分析activity启动流程

最新推荐文章于 2025-03-01 17:55:37 发布

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最新推荐文章于 2025-03-01 17:55:37 发布 · 置顶 · 6.5k 阅读

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#android8.0 #actiivty启动流程

当我们点击桌面图标的时候，会通过Launch应用，启动另外一个进程来启动当前应用的activity。那么这个activity的启动流程是怎样的呢？当然这一部分分为两个关键点：

application启动
activity启动

一、application启动

首先进入ActivityThread.java类。找到main()方法

1、ActivityThread.java----->main()方法，伪代码如下：

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

        Looper.prepareMainLooper();

        ...
        ActivityThread thread = new ActivityThread();
        thread.attach(false, startSeq);

        if (sMainThreadHandler == null) {
   
   
            sMainThreadHandler = thread.getHandler();
        }

        if (false) {
   
   
            Looper.myLooper().setMessageLogging(new
                    LogPrinter(Log.DEBUG, "ActivityThread"));
        }

        // End of event ActivityThreadMain.
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
        Looper.loop();

        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

使用了Handler,looper消息机制，并且初始化了ActivityThread对象，调用了attach方法。

2、ActivityThread.java----->attach()方法，伪代码如下：

@UnsupportedAppUsage
    private void attach(boolean system, long startSeq) {
   
   
            ...
        
            final IActivityManager mgr = ActivityManager.getService();
            try {
   
   
                mgr.attachApplication(mAppThread, startSeq);
            } catch (RemoteException ex) {
   
   
                throw ex.rethrowFromSystemServer();
            }
           ...
    }

使用了Binder机制，得到了ActivityManagerService的服务端代理类，调用attachApplication()方法，就会跨进程调动服务端的该方法。进入ActivityManagerService.java类。

3、ActivityManagerService.java----->attachApplication()方法，伪代码如下：

@Override
    public final void attachApplication(IApplicationThread thread, long startSeq) {
   
   
        synchronized (this) {
   
   
            ...
            attachApplicationLocked(thread, callingPid, callingUid, startSeq);
            ...
        }
    }

间接调用attachApplicationLocked()方法。

4、ActivityManagerService.java----->attachApplicationLocked()方法，伪代码如下：

@GuardedBy("this")
    private final boolean attachApplicationLocked(IApplicationThread thread,
            int pid, int callingUid, long startSeq) {
   
   

            ...
        
            final ActiveInstrumentation instr2 = app.getActiveInstrumentation();
            
            //1、第一步
            
            thread.bindApplication(processName, appInfo, providers,
                instr2.mClass,
                profilerInfo, instr2.mArguments,
                instr2.mWatcher,
                instr2.mUiAutomationConnection, testMode,
                mBinderTransactionTrackingEnabled, enableTrackAllocation,
                isRestrictedBackupMode || !normalMode, app.isPersistent(),
                new Configuration(app.getWindowProcessController().getConfiguration()),
                app.compat, getCommonServicesLocked(app.isolated),
                mCoreSettingsObserver.getCoreSettingsLocked(),
                buildSerial, autofillOptions, contentCaptureOptions);
            ...
        
            if (normalMode) {
   
   
                try {
   
   
                    //2、第二步
                    didSomething = mAtmInternal.