original settings(based on Android 8.1.0)

2019-04-29

入口Activity：com.android.settings.Settings，继承自SettingsActivity

Settings这个类中声明了一系列继承自SettingsActivity的静态内部类，比如 BluetoothSettingsActivity，除此之外，声明都没干，这些类都是干什么用？后面会有答案

SettingsActivity

起点和重点就在这个类：
SettingsActivity extends SettingsDrawerActivity
从onCreate说起：

  @Override
  protected void onCreate(Bundle savedState) {
      super.onCreate(savedState);
      long startTime = System.currentTimeMillis();
      //得到的工厂类实例为com.android.settings.overlay.FeatureFactoryImpl，是在config.xml文件中配置的
      final FeatureFactory factory = FeatureFactory.getFactory(this);
      //factory实际是一个单例，所以以下的provider实际是作用在整个Setting App的生命周期内的
      //DashboardFeatureProvider是用来获取当前设置的项目列表、处理item点击跳转等操作的
      mDashboardFeatureProvider = factory.getDashboardFeatureProvider(this);
      mMetricsFeatureProvider = factory.getMetricsFeatureProvider();
      // 从intent中找到当前Activity在manifest的<metadata>中key 为 com.android.settings.FRAGMENT_CLASS的值
      // 这个值代表了当前Setting Activity的Fragment，mFragmentClass保存起来之后会用到
      // 如果是设置首页，即Settings这个Activity，那么mFragmentClass是null
      // Should happen before any call to getIntent()
      getMetaData();
......
      //当在首页时，mIsShowingDashboard为ture，布局为R.layout.settings_main_dashboard
      setContentView(mIsShowingDashboard ?
              R.layout.settings_main_dashboard : R.layout.settings_main_prefs);
......
      if (savedState != null) {
......
      } else {
          //在首页时显示的Fragment是DashboardSummary
          launchSettingFragment(initialFragmentName, isSubSettings, intent);
      }
      if (mIsShowingDashboard) {
      	//在设置的首页顶部是搜索栏
          findViewById(R.id.search_bar).setVisibility(View.VISIBLE);
          findViewById(R.id.action_bar).setVisibility(View.GONE);
          Toolbar toolbar = findViewById(R.id.search_action_bar);
          toolbar.setOnClickListener(this);
          setActionBar(toolbar);
	......
      }
......
  }

回答上面的一个问题，Settings中的静态内部类，比如BluetoothSettingsActivity等，每个都是在Manifest中注册的一个Activity，它们都完全以依赖父类SettingsActivity的实现，之所以这样做就是为了给Manifest清单文件中提供不同的Activity的类名，并且在首页Settings的DashboardSummary中的RecyclerView中每个item点击时跳转到对应的Activity.

FallbackHome

//TODO

彩蛋

FirmwareVersionPreferenceController 中handlePreferenceTreeClick 处理的，如果在500ms之内点了三次，则跳入彩蛋页面。是这样实现的：

1	private long[] mHits = new long[3];

 @Override
 public boolean handlePreferenceTreeClick(Preference preference) {
     ......
     System.arraycopy(mHits, 1, mHits, 0, mHits.length - 1);
     mHits[mHits.length - 1] = SystemClock.uptimeMillis();
     if (mHits[0] >= (SystemClock.uptimeMillis() - 500)) {
......
         final Intent intent = new Intent(Intent.ACTION_MAIN)
                 .setClassName(
                         "android", com.android.internal.app.PlatLogoActivity.class.getName());
         try {
             mContext.startActivity(intent);
             return true;
         } catch (Exception e) {
             Log.e(TAG, "Unable to start activity " + intent.toString());
         }
     }
     return false;
 }

PlatLogoActivity中就放了一张名为 platlogo的矢量图。这还没完，如果点击五次之后再长按这张奥利奥图片，则进入另外一个彩蛋页，这个Activity经搜索是在一个叫做EasterEgg的单独项目中(com.android.egg.octo.Ocquarium Actrivity)：

im.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               im.setOnLongClickListener(new View.OnLongClickListener() {
                   @Override
                   public boolean onLongClick(View v) {
                       if (mTapCount < 5) return false;
                       final ContentResolver cr = getContentResolver();
                       if (Settings.System.getLong(cr, Settings.System.EGG_MODE, 0)
                               == 0) {
                           // For posterity: the moment this user unlocked the easter egg
                           //也不知道这里记录第一次激活复活节彩蛋是为啥。
                           //for posterity???
                           try {
                               Settings.System.putLong(cr,
                                       Settings.System.EGG_MODE,
                                       System.currentTimeMillis());
                           } catch (RuntimeException e) {
                               Log.e("PlatLogoActivity", "Can't write settings", e);
                           }
                       }
                       im.post(new Runnable() {
                           @Override
                           public void run() {
                               try {
                                   startActivity(new Intent(Intent.ACTION_MAIN)
                                           .setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                                                   | Intent.FLAG_ACTIVITY_CLEAR_TASK
                                                   | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS)
                                           .addCategory("com.android.internal.category.PLATLOGO"));
                               } catch (ActivityNotFoundException ex) {
                                   Log.e("PlatLogoActivity", "No more eggs.");
                               }
                               if (FINISH) finish();
                           }
                       });
                       return true;
                   }
               });
               mTapCount++;
           }
       });

<activity android:name=".octo.Ocquarium"
           android:theme="@android:style/Theme.DeviceDefault.NoActionBar.Fullscreen"
           android:label="@string/app_name">
           <intent-filter>
               <action android:name="android.intent.action.MAIN"/>
               <category android:name="android.intent.category.DEFAULT" />
               <category android:name="com.android.internal.category.PLATLOGO" />
           </intent-filter>
       </activity>