Activity启动过程

启动activity:
**android.process.acore进程
1.Acticity.startActivityForResult()
2.Instrumention.execStartActivity();
3.ActivityManagerNative.getDefault()
                .startActivity()
  3.1 ActivityManagerNative.getDefault()返回的是ActivityManagerProxy的实例,
  它只是一个代理类,这个代理类实际上代理的是IBinder b = ServiceManager.getService("activity");
  这个Service。
  3.2 这个Service是什么时候添加进来的呢?
  在SystemServer.java的run()中有调用
  ActivityManagerService.setSystemProcess();
      ServiceManager.addService("activity", m);
      这里还会添加许多系统关键服务。
      (TODO:查看在SystemServer的Log输出)
     
**system_process进程
4 ActivityManagerNative
    |--ActivityManagerService
   
    在ActivityManagerNative的onTransact方法中最终提供了服务:
    case START_ACTIVITY_TRANSACTION:
      ActivityManagerService.startActivity();
        --startActivityLocked(IApplicationThread caller,
            Intent intent, String resolvedType,
            Uri[] grantedUriPermissions,
            int grantedMode, ActivityInfo aInfo, IBinder resultTo,
            String resultWho, int requestCode,
            int callingPid, int callingUid, boolean onlyIfNeeded,
            boolean componentSpecified)
          --startActivityUncheckedLocked(r, sourceRecord,
                grantedUriPermissions, grantedMode, onlyIfNeeded, true)
          在这个方法里面检查权限,解析intent中的Flag。。。
          --startActivityLocked(HistoryRecord r, boolean newTask)
            --resumeTopActivityLocked(HistoryRecord prev)
              --startSpecificActivityLocked(HistoryRecord r,boolean andResume, boolean checkConfig)
                --startProcessLocked(String processName,ApplicationInfo info, boolean knownToBeDead, int intentFlags,String hostingType, ComponentName hostingName)
                  --startProcessLocked(ProcessRecord app,String hostingType, String hostingNameStr)
                    在这里启动一个进程用来host这个应用
                    int pid = Process.start("android.app.ActivityThread",
                    mSimpleProcessManagement ? app.processName : null, uid, uid,
                    gids, debugFlags, null);
                   
ActivityManagerService.java
--startSpecificActivityLocked(HistoryRecord r,boolean andResume, boolean checkConfig)
  --realStartActivityLocked(HistoryRecord r,ProcessRecord app, boolean andResume, boolean checkConfig)
    --app.thread.scheduleLaunchActivity                                   //scheduleLaunchActivity()@IApplicationThread.java
      --scheduleLaunchActivity()@ActivityThread.java                      //这里实际是ApplicationThreadNative提供的服务
        --handleMessage()@H$ActivityThread.java
          --handleLaunchActivity()@ActivityThread.java
            --Activity performLaunchActivity(ActivityRecord r, Intent customIntent)@ActivityThread.java  //这时真正的Activity对象被构造出来
              --mInstrumentation.newActivity()                            //通过反射构造出Activity对象
              --activity.attach()                                         //初始化Activity,生成一个window对象,设置各种状态等等
              --mInstrumentation.callActivityOnCreate(activity, r.state);  //调用Activity的onCreate()方法
           
              到这里,我们自己写的activity的onCreate()方法已经被系统调用了,接下来依次回调生命周期方法:
              --activity.performStart();
                --mInstrumentation.callActivityOnStart(this);
              --mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
              --mInstrumentation.callActivityOnPostCreate(activity, r.state);
              --mActivities.put(r.token, r);                               //将这个activity入栈
             
            然后就要调用onResume()方法了:
            --handleResumeActivity(IBinder token, boolean clearHide, boolean isForward)
              --performResumeActivity(token, clearHide);
                --r.activity.performResume();
                  --performRestart()@Activity.java;
                    --mInstrumentation.callActivityOnRestart(this);
                    --mInstrumentation.callActivityOnStart(this);
                --mInstrumentation.callActivityOnResume(this);
                onResume()已经调用完毕,一个activity的逻辑处理结束了,但是这时候屏幕上还不会显示任何东西,因为View还没有添加进去
               
               
              --r.window.getDecorView();                                   //开始把DecorView添加进Window
              --wm.addView(decor, l);
           
            至此一个Activity启动结束。

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