android:configChange

1. 当转屏时，系统会调用ams.setRequestedOrientation

    public void setRequestedOrientation(IBinder token,
            int requestedOrientation) {
        synchronized (this) {
            ActivityRecord r = mMainStack.isInStackLocked(token);
            if (r == null) {
                return;
            }
            ......
            mWindowManager.setAppOrientation(r.appToken, requestedOrientation);
            Configuration config = mWindowManager.updateOrientationFromAppTokens(
                    mConfiguration,
                    r.mayFreezeScreenLocked(r.app) ? r.appToken : null);
            if (config != null) {
                r.frozenBeforeDestroy = true;
                if (!updateConfigurationLocked(config, r, false, false)) {
                    mMainStack.resumeTopActivityLocked(null);
                }
            }
            ......
        }
    }
   
2. 调用ams.updateConfigurationLocked

 boolean updateConfigurationLocked(Configuration values,
            ......       
        boolean kept = true;
       
        if (values != null) {
            Configuration newConfig = new Configuration(mConfiguration);
            changes = newConfig.updateFrom(values);
            if (changes != 0) {
                ......
                for (int i=mLruProcesses.size()-1; i>=0; i--) {
                    ProcessRecord app = mLruProcesses.get(i);
                    try {
                        if (app.thread != null) {
                            if (DEBUG_CONFIGURATION) Slog.v(TAG, "Sending to proc "
                                    + app.processName + " new config " + mConfiguration);
                            app.thread.scheduleConfigurationChanged(configCopy);
                        }
                    } catch (Exception e) {
                    }
                }
                ......
        }
       
        if (changes != 0 && starting == null) {
            // If the configuration changed, and the caller is not already
            // in the process of starting an activity, then find the top
            // activity to check if its configuration needs to change.
            starting = mMainStack.topRunningActivityLocked(null);
        }
       
        if (starting != null) {
            kept = mMainStack.ensureActivityConfigurationLocked(starting, changes);
            // And we need to make sure at this point that all other activities
            // are made visible with the correct configuration.
            mMainStack.ensureActivitiesVisibleLocked(starting, changes);
        }
       
        if (values != null && mWindowManager != null) {
            mWindowManager.setNewConfiguration(mConfiguration);
        }
       
        return kept;
    }

   会调用activitythread.scheduleConfigurationChanged,在这个方法中会判断是否由Activity自己处理config change，如果是在Activity的confiChange中声明的则由Activity的onConfigChanged方法处理
   接下来调用activitythread.scheduleConfigurationChanged，如果返回false则要销毁当前的activity，调用activitystack.relaunchActivityLocked销毁当前的activity，然后重新创建，；如果返回true则不会销毁当前的activity，进而就不会调用Activity的生命周期回调方法，当前发生改变的config是在Activity的configChange属性中声明的则说明由Activity的onConfigChanged来处理，不销毁当前activity
  
final boolean ensureActivityConfigurationLocked(ActivityRecord r,
            int globalChanges) {
        ......
        if ((changes&(~r.info.getRealConfigChanged())) != 0 || r.forceNewConfig) {
            // Aha, the activity isn't handling the change, so DIE DIE DIE.
            r.configChangeFlags |= changes;
            r.startFreezingScreenLocked(r.app, globalChanges);
            r.forceNewConfig = false;
            if (r.app == null || r.app.thread == null) {
                if (DEBUG_SWITCH || DEBUG_CONFIGURATION) Slog.v(TAG,
                        "Config is destroying non-running " + r);
                destroyActivityLocked(r, true, false, "config");
            } else if (r.state == ActivityState.PAUSING) {
                // A little annoying: we are waiting for this activity to
                // finish pausing.  Let's not do anything now, but just
                // flag that it needs to be restarted when done pausing.
                if (DEBUG_SWITCH || DEBUG_CONFIGURATION) Slog.v(TAG,
                        "Config is skipping already pausing " + r);
                r.configDestroy = true;
                return true;
            } else if (r.state == ActivityState.RESUMED) {
                // Try to optimize this case: the configuration is changing
                // and we need to restart the top, resumed activity.
                // Instead of doing the normal handshaking, just say
                // "restart!".
                if (DEBUG_SWITCH || DEBUG_CONFIGURATION) Slog.v(TAG,
                        "Config is relaunching resumed " + r);
                //销毁重建
                relaunchActivityLocked(r, r.configChangeFlags, true);
                r.configChangeFlags = 0;
            } else {
                //销毁重建
                relaunchActivityLocked(r, r.configChangeFlags, false);
                r.configChangeFlags = 0;
            }

            // All done...  tell the caller we weren't able to keep this
            // activity around.
            return false;
        }
        ......

        return true;
    }
  

3. 在ams.updateConfigurationLocked返回false的情况下(即创建新的Activity)，调用activitystack.resumeTopActivityLocked显示新创建的Activity