android源码分析(一) - 语言切换机制

android语言切换是在packages/apps/Settings/com/android/settings/LocalePicker.java的updateLocale()函数中调用.

 /**
      * Requests the system to update the system locale. Note that the system looks halted
      * for a while during the Locale migration, so the caller need to take care of it.
      */
     public static void updateLocale(Locale locale) {
         try {
             IActivityManager am = ActivityManagerNative.getDefault();
             Configuration config = am.getConfiguration();

             config.locale = locale;

             // indicate this isn't some passing default - the user wants this remembered
             config.userSetLocale = true;

             am.updateConfiguration(config);
             // Trigger the dirty bit for the Settings Provider.
             BackupManager.dataChanged("com.android.providers.settings");
         } catch (RemoteException e) {
             // Intentionally left blank
         }
     }

 从注释可以看出, 只要本地local改变就会调用该函数. 查看ActivityManagerNative的getDefault()可以看到, 该函数返回的是远程服务对象ActivityManagerServices.java在本地的一个代理.  最终调用的是ActivityManagerService.java中的updateConfiguration()函数. 

 public void updateConfiguration(Configuration values) {
         enforceCallingPermission(android.Manifest.permission.CHANGE_CONFIGURATION,
                 "updateConfiguration()");

         synchronized(this) {
             if (values == null && mWindowManager != null) {
                 // sentinel: fetch the current configuration from the window manager
                 values = mWindowManager.computeNewConfiguration();
             }

             if (mWindowManager != null) {
                 mProcessList.applyDisplaySize(mWindowManager);
             }

             final long origId = Binder.clearCallingIdentity();
             if (values != null) {
                 Settings.System.clearConfiguration(values);
             }
             updateConfigurationLocked(values, null, false, false);
             Binder.restoreCallingIdentity(origId);
         }
     }

 该函数, 首先进行的是权限的校验. 然后调用updateConfigurationLocked()函数. 

 

 /**
      * Do either or both things: (1) change the current configuration, and (2)
      * make sure the given activity is running with the (now) current
      * configuration.  Returns true if the activity has been left running, or
      * false if <var>starting</var> is being destroyed to match the new
      * configuration.
      * @param persistent TODO
      */
     public boolean updateConfigurationLocked(Configuration values,
             ActivityRecord starting, boolean persistent, boolean initLocale) {
         int changes = 0;

         boolean kept = true;

         if (values != null) {
             Configuration newConfig = new Configuration(mConfiguration);
             changes = newConfig.updateFrom(values);
             if (changes != 0) {
                 if (DEBUG_SWITCH || DEBUG_CONFIGURATION) {
                     Slog.i(TAG, "Updating configuration to: " + values);
                 }

                 EventLog.writeEvent(EventLogTags.CONFIGURATION_CHANGED, changes);

                 if (values.locale != null && !initLocale) {
                     saveLocaleLocked(values.locale,
                                      !values.locale.equals(mConfiguration.locale),
                                      values.userSetLocale, values.simSetLocale);
                 }


                 mConfigurationSeq++;
                 if (mConfigurationSeq <= 0) {
                     mConfigurationSeq = 1;
                 }
                 newConfig.seq = mConfigurationSeq;
                 mConfiguration = newConfig;
                 Slog.i(TAG, "Config changed: " + newConfig);

                 final Configuration configCopy = new Configuration(mConfiguration);

                 AttributeCache ac = AttributeCache.instance();
                 if (ac != null) {
                     ac.updateConfiguration(configCopy);
                 }

                 // Make sure all resources in our process are updated
                 // right now, so that anyone who is going to retrieve
                 // resource values after we return will be sure to get
                 // the new ones.  This is especially important during
                 // boot, where the first config change needs to guarantee
                 // all resources have that config before following boot
                 // code is executed.
                 mSystemThread.applyConfigurationToResources(configCopy);

                 if (persistent && Settings.System.hasInterestingConfigurationChanges(changes)) {
                     Message msg = mHandler.obtainMessage(UPDATE_CONFIGURATION_MSG);
                     msg.obj = new Configuration(configCopy);
                     mHandler.sendMessage(msg);
                 }

                 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) {
                     }
                 }
                 Intent intent = new Intent(Intent.ACTION_CONFIGURATION_CHANGED);
                 intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                         | Intent.FLAG_RECEIVER_REPLACE_PENDING);
                 broadcastIntentLocked(null, null, intent, null, null, 0, null, null,
                         null, false, false, MY_PID, Process.SYSTEM_UID);
                 if ((changes&ActivityInfo.CONFIG_LOCALE) != 0) {
                     broadcastIntentLocked(null, null,
                             new Intent(Intent.ACTION_LOCALE_CHANGED),
                             null, null, 0, null, null,
                             null, false, false, MY_PID, Process.SYSTEM_UID);
                 }

             }
         }

         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;
     }

整个语言切换就在这个函数中完成. 咋一看似乎没感觉到该函数做了哪些事情. 我们首先来看注释: Do either or both things: (1) change the current configuration, and (2)
 make sure the given activity is running with the (now) current. configuration大概意思是: 这个函数做了两件事情. (1). 改变当前的configuration. 意思就是让改变的configuration更新到当前configuration. (2) 确保所有正在运行的activity都能更新改变后的configuration.(这点是关键.) . 我们按照这个思路看看android是如何更新configuration. 查看代码 , 首先看到 这个函数首先判断values是否为空, 这里values肯定不为空的, 然后changes = newConfig.updateFrom(values); 我们看看updateFrom做了什么操作.

 /**
      * Copy the fields from delta into this Configuration object, keeping
      * track of which ones have changed.  Any undefined fields in
      * <var>delta</var> are ignored and not copied in to the current
      * Configuration.
      * @return Returns a bit mask of the changed fields, as per
      * {@link #diff}.
      */
     public int updateFrom(Configuration delta) {
         int changed = 0;
         ...
         if (delta.locale != null
                 && (locale == null || !locale.equals(delta.locale))) {
             changed |= ActivityInfo.CONFIG_LOCALE;
             locale = delta.locale != null
                     ? (Locale) delta.locale.clone() : null;
             textLayoutDirection = LocaleUtil.getLayoutDirectionFromLocale(locale);
         }
         if (delta.userSetLocale && (!userSetLocale || ((changed & ActivityInfo.CONFIG_LOCALE) != 0)))
         {
             userSetLocale = true;
             changed |= ActivityInfo.CONFIG_LOCALE;
         }
         ...
         return changed;
     }

因为语言改变了, 那么 (!locale.equals(delta.locale)) 是true. changed 大于0, 然后return changed. 回到ActivityManagerService.java的updateConfigurationLocked函数, 因为changed不为0 , 所以走if这个流程.  继续看代码

 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) {
                     }
                 }

首先看到的是mLurProcesses 是ArrayList<ProcessRecord>类型.  LRU : Least Recently Used保存所有运行过的进程.  ProcessRecord进程类, 一个apk文件运行时会对应一个进程. app.thread. 此处的thread代表的是ApplicationThreadNative.java类型.  然后调用其scheduleConfigurationChanged();  查看该函数

 public final void scheduleConfigurationChanged(Configuration config)
             throws RemoteException {
         Parcel data = Parcel.obtain();
         data.writeInterfaceToken(IApplicationThread.descriptor);
         config.writeToParcel(data, 0);
         mRemote.transact(SCHEDULE_CONFIGURATION_CHANGED_TRANSACTION, data, null,
                 IBinder.FLAG_ONEWAY);
         data.recycle();
     }

 
又是通过binder调用, 所以 , binder在android中是一个很重要的概念. 此处远程调用的是ActivityThread.java中的私有内部内ApplicationThread

   private class ApplicationThread extends ApplicationThreadNative {
         private static final String HEAP_COLUMN = "%13s %8s %8s %8s %8s %8s %8s";
         private static final String ONE_COUNT_COLUMN = "%21s %8d";
         private static final String TWO_COUNT_COLUMNS = "%21s %8d %21s %8d";
         private static final String TWO_COUNT_COLUMNS_DB = "%21s %8d %21s %8d";
         private static final String DB_INFO_FORMAT = "  %8s %8s %14s %14s  %s";


         ...
         public void scheduleConfigurationChanged(Configuration config) {
             updatePendingConfiguration(config);
             queueOrSendMessage(H.CONFIGURATION_CHANGED, config);
         }
         ...
 }

而ApplicationThread中的handler的CONFIGURATION_CHANGED是调用handleConfigurationChanged()

 final void handleConfigurationChanged(Configuration config, CompatibilityInfo compat) {

        ArrayList<ComponentCallbacks2> callbacks = null;

     ...         ...
        applyConfigurationToResourcesLocked(config, compat);

        ...

        callbacks = collectComponentCallbacksLocked(false, config);
        ...

        if (callbacks != null) {
            final int N = callbacks.size();
            for (int i=0; i<N; i++) {
                performConfigurationChanged(callbacks.get(i), config);
            }
        }

这个函数首先是调用applyConfigurationToResourcesLocked(). 看函数名大概可以推测: 将configuration应用到resources.这里configuration改变的是local 本地语言. 那而resources资源包含不就包含了语言, 图片这些资源吗. 

 final boolean applyConfigurationToResourcesLocked(Configuration config,
             CompatibilityInfo compat) {

         int changes = mResConfiguration.updateFrom(config);
         DisplayMetrics dm = getDisplayMetricsLocked(null, true);


         if (compat != null && (mResCompatibilityInfo == null ||
                 !mResCompatibilityInfo.equals(compat))) {
             mResCompatibilityInfo = compat;
             changes |= ActivityInfo.CONFIG_SCREEN_LAYOUT
                     | ActivityInfo.CONFIG_SCREEN_SIZE
                     | ActivityInfo.CONFIG_SMALLEST_SCREEN_SIZE;
         }

         ...

         Resources.updateSystemConfiguration(config, dm, compat);

         ...

         Iterator<WeakReference<Resources>> it =
             mActiveResources.values().iterator();
         while (it.hasNext()) {
             WeakReference<Resources> v = it.next();
             Resources r = v.get();
             if (r != null) {
                 if (DEBUG_CONFIGURATION) Slog.v(TAG, "Changing resources "
                         + r + " config to: " + config);
                 r.updateConfiguration(config, dm, compat);
                 //Slog.i(TAG, "Updated app resources " + v.getKey()
                 //        + " " + r + ": " + r.getConfiguration());
             } else {
                 //Slog.i(TAG, "Removing old resources " + v.getKey());
                 it.remove();
             }
         }

         return changes != 0;
     }

Resources.updateSystemConfiguration()清除一部分系统资源, 并且将config更新到Resources, 而Resources包含了一个AssetManager对象, 该对象的核心实现是在AssetManager.cpp中完成的. 然后循环清空mActivityResources资源. 再回到handleConfigurationChanged()函数, 执行完updateSystemConfiguration后, 会循环该进程的所有activity:

if (callbacks != null) {

            final int N = callbacks.size();
            for (int i=0; i<N; i++) {
                performConfigurationChanged(callbacks.get(i), config);
            }
        }

再来看performConfigurationChanged的实现:

 private final void performConfigurationChanged(
             ComponentCallbacks2 cb, Configuration config) {
         // Only for Activity objects, check that they actually call up to their
         // superclass implementation.  ComponentCallbacks2 is an interface, so
         // we check the runtime type and act accordingly.
         Activity activity = (cb instanceof Activity) ? (Activity) cb : null;
         if (activity != null) {
             activity.mCalled = false;
         }

         boolean shouldChangeConfig = false;
         if ((activity == null) || (activity.mCurrentConfig == null)) {
             shouldChangeConfig = true;
         } else {

             // If the new config is the same as the config this Activity
             // is already running with then don't bother calling
             // onConfigurationChanged
             int diff = activity.mCurrentConfig.diff(config);
             if (diff != 0) {
                 // If this activity doesn't handle any of the config changes
                 // then don't bother calling onConfigurationChanged as we're
                 // going to destroy it.
                 if ((~activity.mActivityInfo.getRealConfigChanged() & diff) == 0) {
                     shouldChangeConfig = true;
                 }
             }
         }

         if (DEBUG_CONFIGURATION) Slog.v(TAG, "Config callback " + cb
                 + ": shouldChangeConfig=" + shouldChangeConfig);
         if (shouldChangeConfig) {
             cb.onConfigurationChanged(config);

             if (activity != null) {
                 if (!activity.mCalled) {
                     throw new SuperNotCalledException(
                             "Activity " + activity.getLocalClassName() +
                         " did not call through to super.onConfigurationChanged()");
                 }
                 activity.mConfigChangeFlags = 0;
                 activity.mCurrentConfig = new Configuration(config);
             }
         }
     }

该函数判断configuration是否改变, 如果改变那么shouldChangeConfig为true. 然后调用activity的onConfigurationChange(config);

 /**
     * Called by the system when the device configuration changes while your
     * activity is running.  Note that this will <em>only</em> be called if
     * you have selected configurations you would like to handle with the
     * {@link android.R.attr#configChanges} attribute in your manifest.  If
     * any configuration change occurs that is not selected to be reported
     * by that attribute, then instead of reporting it the system will stop
     * and restart the activity (to have it launched with the new
     * configuration).
     *
     * <p>At the time that this function has been called, your Resources
     * object will have been updated to return resource values matching the
     * new configuration.
     *
     * @param newConfig The new device configuration.
     */
    public void onConfigurationChanged(Configuration newConfig) {
        mCalled = true;

        mFragments.dispatchConfigurationChanged(newConfig);

        if (mWindow != null) {
            // Pass the configuration changed event to the window
            mWindow.onConfigurationChanged(newConfig);
        }

        if (mActionBar != null) {
            // Do this last; the action bar will need to access
            // view changes from above.
            mActionBar.onConfigurationChanged(newConfig);
        }
    }

查看注释, 大概意思是:  如果你的activity运行 , 设备信息有改变(即configuration改变)时由系统调用. 如果你在manifest.xml中配置了configChnages属性则表示有你自己来处理configuration change. 否则就重启当前这个activity.  而重启之前, 旧的resources已经被清空, 那么就会装载新的资源, 整个过程就完成了语言切换后 , 能够让所有app使用新的语言. 语言切换流程大概分为三步:

第一步:  判断configuration的local是否已经改变, 如果改变则将local更新到当前的configuration

第二步: 清空旧的资源. 

第三步: 重启所有所有进程并加装新资源.

由于个人知识水平有限, 有些地方不免有些纰漏, 希望大牛多多指点.  也希望有共同兴趣爱好的人进行技术交流.