分析Android 11.0Settings源码之主界面加载

本篇主要记录AndroidR Settings源码主界面加载流程，方便后续工作调试其流程。

Settings代码路径：

packages/app/Settings/

Settings代码获取：

Setting 源码下载地址：https://github.com/aosp-mirror/platform_packages_apps_settings
git地址：https://github.com/aosp-mirror/platform_packages_apps_settings.git

主界面加载：

首先我们来看 Settings 模块中的 AndroidManifest.xml 文件，找到默认启动入口Activity信息：

<activity android:name=".homepage.SettingsHomepageActivity"
      android:label="@string/settings_label_launcher"
      android:theme="@style/Theme.Settings.Home"
      android:taskAffinity="com.android.settings.root"
      android:launchMode="singleTask"
      android:configChanges="keyboard|keyboardHidden">
<intent-filter android:priority="1">
    <action android:name="android.settings.SETTINGS" />
    <category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data android:name="com.android.settings.PRIMARY_PROFILE_CONTROLLED"
           android:value="true" />
</activity>
//activity-alias可用来设置某个Activity的快捷入口，可以放在桌面上或者通过该别名被其他组件快速调起。                   
//android:targetActivity为目标Activity. 
<!-- Alias for launcher activity only, as this belongs to each profile. -->
<activity-alias android:name="Settings"
    android:label="@string/settings_label_launcher"
    android:taskAffinity="com.android.settings.root"
    android:launchMode="singleTask"
    android:targetActivity=".homepage.SettingsHomepageActivity">
<intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<meta-data android:name="android.app.shortcuts" android:resource="@xml/shortcuts"/>
</activity-alias>

可以看到Settings的桌面图标启动的主界面是Settings.java，但其xml定义了targetActivity属性，实质应是SettingsHomepageActivity.java，从onCreate()方法开始:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.settings_homepage_container);
    final View root = findViewById(R.id.settings_homepage_container);
    root.setSystemUiVisibility(
            View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_LAYOUT_STABLE);

    setHomepageContainerPaddingTop();

    final Toolbar toolbar = findViewById(R.id.search_action_bar);
    FeatureFactory.getFactory(this).getSearchFeatureProvider()
            .initSearchToolbar(this /* activity */, toolbar, SettingsEnums.SETTINGS_HOMEPAGE);

    final ImageView avatarView = findViewById(R.id.account_avatar);
    getLifecycle().addObserver(new AvatarViewMixin(this, avatarView));
    getLifecycle().addObserver(new HideNonSystemOverlayMixin(this));

    if (!getSystemService(ActivityManager.class).isLowRamDevice()) {
        // Only allow contextual feature on high ram devices.
        showFragment(new ContextualCardsFragment(), R.id.contextual_cards_content);
    }
    showFragment(new TopLevelSettings(), R.id.main_content);
    ((FrameLayout) findViewById(R.id.main_content))
            .getLayoutTransition().enableTransitionType(LayoutTransition.CHANGING);
}

可以看到主界面的layout为settings_homepage_container.xml:

<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/settings_homepage_container"
    android:fitsSystemWindows="true"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.core.widget.NestedScrollView
        android:id="@+id/main_content_scrollable_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="com.android.settings.widget.FloatingAppBarScrollingViewBehavior">

        <LinearLayout
            android:id="@+id/homepage_container"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <FrameLayout
                android:id="@+id/contextual_cards_content"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="@dimen/contextual_card_side_margin"
                android:layout_marginEnd="@dimen/contextual_card_side_margin"/>

            <FrameLayout
                android:id="@+id/main_content"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:animateLayoutChanges="true"
                android:background="?android:attr/windowBackground"/>

        </LinearLayout>
    </androidx.core.widget.NestedScrollView>

    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:touchscreenBlocksFocus="false"
        android:keyboardNavigationCluster="false">
        <include layout="@layout/search_bar"/>
    </com.google.android.material.appbar.AppBarLayout>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

主界面布局中主要包含两部分：一个顶部快捷搜索栏，一个Id为main_content的FrameLayout就是用来显示主设置内容的，即Settings的一级菜单项界面。
回到onCreate()方法：

showFragment(new TopLevelSettings(), R.id.main_content);

可以看到一级菜单启动的是TopLevelSettings，TopLevelSettings继承于DashboardFragment.java：

public class TopLevelSettings extends DashboardFragment implements
PreferenceFragmentCompat.OnPreferenceStartFragmentCallback

TopLevelSettings的构造方法：

public TopLevelSettings() {
    final Bundle args = new Bundle();
    // Disable the search icon because this page uses a full search view in actionbar.
    args.putBoolean(NEED_SEARCH_ICON_IN_ACTION_BAR, false);
    setArguments(args);
}

可以看到通过构造方法传递了一个参数，从注释中可以看出，该参数的用意是由于主界面使用完整的搜索视图所以在主界面的actionbar中隐藏了搜索图标。然后再根据framgments生命周期先来看onAttach()方法:

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    use(SupportPreferenceController.class).setActivity(getActivity());
}

调用父类DashboardFragment.java的onAttach()方法：

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    mSuppressInjectedTileKeys = Arrays.asList(context.getResources().getStringArray(
            R.array.config_suppress_injected_tile_keys));
    mDashboardFeatureProvider = FeatureFactory.getFactory(context).
            getDashboardFeatureProvider(context);
    // Load preference controllers from code
    final List<AbstractPreferenceController> controllersFromCode =
            createPreferenceControllers(context);
    // Load preference controllers from xml definition
    final List<BasePreferenceController> controllersFromXml = PreferenceControllerListHelper
            .getPreferenceControllersFromXml(context, getPreferenceScreenResId());
    // Filter xml-based controllers in case a similar controller is created from code already.
    final List<BasePreferenceController> uniqueControllerFromXml =
            PreferenceControllerListHelper.filterControllers(
                    controllersFromXml, controllersFromCode);

    // Add unique controllers to list.
    if (controllersFromCode != null) {
        mControllers.addAll(controllersFromCode);
    }
    mControllers.addAll(uniqueControllerFromXml);

    // And wire up with lifecycle.
    final Lifecycle lifecycle = getSettingsLifecycle();
    uniqueControllerFromXml.forEach(controller -> {
        if (controller instanceof LifecycleObserver) {
            lifecycle.addObserver((LifecycleObserver) controller);
        }
    });

    // Set metrics category for BasePreferenceController.
    final int metricCategory = getMetricsCategory();
    mControllers.forEach(controller -> {
        if (controller instanceof BasePreferenceController) {
            ((BasePreferenceController) controller).setMetricsCategory(metricCategory);
        }
    });

    mPlaceholderPreferenceController =
            new DashboardTilePlaceholderPreferenceController(context);
    mControllers.add(mPlaceholderPreferenceController);
    for (AbstractPreferenceController controller : mControllers) {
        addPreferenceController(controller);
    }
}

通过方法注释可以得知此方法主要是完成preference controllers的加载。
DashboardFragment.java的onCreate()方法：

@Override
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    // Set ComparisonCallback so we get better animation when list changes.
    getPreferenceManager().setPreferenceComparisonCallback(
            new PreferenceManager.SimplePreferenceComparisonCallback());
    if (icicle != null) {
        // Upon rotation configuration change we need to update preference states before any
        // editing dialog is recreated (that would happen before onResume is called).
        updatePreferenceStates();
    }
}

设置ComparisonCallback，以便在列表更改时获得更好的动画效果。
第一次进入时，icicle为null，根据log定位发现，其后调用DashboardFragment.java的onCreatePreferences()方法：

@Override
public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
    checkUiBlocker(mControllers);
    refreshAllPreferences(getLogTag());
    mControllers.stream()
            .map(controller -> (Preference) findPreference(controller.getPreferenceKey()))
            .filter(Objects::nonNull)
            .forEach(preference -> {
                // Give all controllers a chance to handle click.
                preference.getExtras().putInt(CATEGORY, getMetricsCategory());
            });
}

调用refreshAllPreferences()：

/**
 * Refresh all preference items, including both static prefs from xml, and dynamic items from
 * DashboardCategory.
 */
private void refreshAllPreferences(final String tag) {
    final PreferenceScreen screen = getPreferenceScreen();
    // First remove old preferences.
    if (screen != null) {
        // Intentionally do not cache PreferenceScreen because it will be recreated later.
        screen.removeAll();
    }

    // Add resource based tiles.
    displayResourceTiles();

    refreshDashboardTiles(tag);

    final Activity activity = getActivity();
    if (activity != null) {
        Log.d(tag, "All preferences added, reporting fully drawn");
        activity.reportFullyDrawn();
    }

    updatePreferenceVisibility(mPreferenceControllers);
}

刷新所有preference items，包括来自xml的静态preference和来自DashboardCategory的动态preference，静态xml定义的prefs(调用displayResourceTiles()方法)，动态DashboardCategory动态加载(调用refreshDashboardTiles(TAG)方法，其中TAG为 “TopLevelSettings”)。
displayResourceTiles()：此方法主要是从xml资源文件中加载显示prefs：

/**
 * Displays resource based tiles.
 */
private void displayResourceTiles() {
    final int resId = getPreferenceScreenResId();
    if (resId <= 0) {
        return;
    }
    addPreferencesFromResource(resId);
    final PreferenceScreen screen = getPreferenceScreen();
    screen.setOnExpandButtonClickListener(this);
    displayResourceTilesToScreen(screen);
}
/**
 * Perform {@link AbstractPreferenceController#displayPreference(PreferenceScreen)}
 * on all {@link AbstractPreferenceController}s.
 */
protected void displayResourceTilesToScreen(PreferenceScreen screen) {
    mPreferenceControllers.values().stream().flatMap(Collection::stream).forEach(
            controller -> controller.displayPreference(screen));
}

静态加载

首先调用getPreferenceScreenResId()方法获取所要加载的xml的ID，然后调用子类TopLevelSettings.java的getPreferenceScreenResId()方法：

@Override
protected int getPreferenceScreenResId() {
    return R.xml.top_level_settings;
}

可以看到Settings主界面加载的xml文件是top_level_settings：

<PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:settings="http://schemas.android.com/apk/res-auto"
    android:key="top_level_settings">

    <Preference
        android:key="top_level_network"
        android:title="@string/network_dashboard_title"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_network"
        android:order="-120"
        android:fragment="com.android.settings.network.NetworkDashboardFragment"
        settings:controller="com.android.settings.network.TopLevelNetworkEntryPreferenceController"/>

    <Preference
        android:key="top_level_connected_devices"
        android:title="@string/connected_devices_dashboard_title"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_connected_device"
        android:order="-110"
        android:fragment="com.android.settings.connecteddevice.ConnectedDeviceDashboardFragment"
        settings:controller="com.android.settings.connecteddevice.TopLevelConnectedDevicesPreferenceController"/>

    <Preference
        android:key="top_level_apps_and_notifs"
        android:title="@string/app_and_notification_dashboard_title"
        android:summary="@string/app_and_notification_dashboard_summary"
        android:icon="@drawable/ic_homepage_apps"
        android:order="-100"
        android:fragment="com.android.settings.applications.AppAndNotificationDashboardFragment"/>

    <Preference
        android:key="top_level_battery"
        android:title="@string/power_usage_summary_title"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_battery"
        android:fragment="com.android.settings.fuelgauge.PowerUsageSummary"
        android:order="-90"
        settings:controller="com.android.settings.fuelgauge.TopLevelBatteryPreferenceController"/>

    <Preference
        android:key="top_level_display"
        android:title="@string/display_settings"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_display"
        android:order="-80"
        android:fragment="com.android.settings.DisplaySettings"
        settings:controller="com.android.settings.display.TopLevelDisplayPreferenceController"/>

    <Preference
        android:key="top_level_sound"
        android:title="@string/sound_settings"
        android:summary="@string/sound_dashboard_summary"
        android:icon="@drawable/ic_homepage_sound"
        android:order="-70"
        android:fragment="com.android.settings.notification.SoundSettings"/>

    <Preference
        android:key="top_level_storage"
        android:title="@string/storage_settings"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_storage"
        android:order="-60"
        android:fragment="com.android.settings.deviceinfo.StorageSettings"
        settings:controller="com.android.settings.deviceinfo.TopLevelStoragePreferenceController"/>

    <Preference
        android:key="top_level_privacy"
        android:title="@string/privacy_dashboard_title"
        android:summary="@string/privacy_dashboard_summary"
        android:icon="@drawable/ic_homepage_privacy"
        android:order="-55"
        android:fragment="com.android.settings.privacy.PrivacyDashboardFragment"/>

    <Preference
        android:key="top_level_location"
        android:title="@string/location_settings_title"
        android:summary="@string/location_settings_loading_app_permission_stats"
        android:icon="@drawable/ic_homepage_location"
        android:order="-50"
        android:fragment="com.android.settings.location.LocationSettings"
        settings:controller="com.android.settings.location.TopLevelLocationPreferenceController"/>

    <Preference
        android:key="top_level_security"
        android:title="@string/security_settings_title"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_security"
        android:order="-40"
        android:fragment="com.android.settings.security.SecuritySettings"
        settings:controller="com.android.settings.security.TopLevelSecurityEntryPreferenceController"/>

    <Preference
        android:key="top_level_accounts"
        android:title="@string/account_dashboard_title"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_accounts"
        android:order="-30"
        android:fragment="com.android.settings.accounts.AccountDashboardFragment"
        settings:controller="com.android.settings.accounts.TopLevelAccountEntryPreferenceController"/>

    <Preference
        android:key="top_level_accessibility"
        android:title="@string/accessibility_settings"
        android:summary="@string/accessibility_settings_summary"
        android:icon="@drawable/ic_homepage_accessibility"
        android:order="-20"
        android:fragment="com.android.settings.accessibility.AccessibilitySettings"
        settings:controller="com.android.settings.accessibility.TopLevelAccessibilityPreferenceController"/>

    <Preference
        android:key="top_level_system"
        android:title="@string/header_category_system"
        android:summary="@string/system_dashboard_summary"
        android:icon="@drawable/ic_homepage_system_dashboard"
        android:order="10"
        android:fragment="com.android.settings.system.SystemDashboardFragment"/>

    <Preference
        android:key="top_level_about_device"
        android:title="@string/about_settings"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_homepage_about"
        android:order="20"
        android:fragment="com.android.settings.deviceinfo.aboutphone.MyDeviceInfoFragment"
        settings:controller="com.android.settings.deviceinfo.aboutphone.TopLevelAboutDevicePreferenceController"/>

    <Preference
        android:key="top_level_support"
        android:summary="@string/support_summary"
        android:title="@string/page_tab_title_support"
        android:icon="@drawable/ic_homepage_support"
        android:order="100"
        settings:controller="com.android.settings.support.SupportPreferenceController"/>

</PreferenceScreen>

可以看到主要配置的是一些Preference菜单项如网络和互联网、已连接的设备、应用和通知、电池等等，Preference的配置含义：

key：唯一性ID；
title：标题；
summary：简介；
ico：图标；
order：加载显示优先级，order为负时，绝对值越高，界面显示越靠前；order为正时，值越高，显示越靠后；
fragment：点击此preference所跳转的fragment界面；
controller：控制管理类。

动态加载

refreshDashboardTiles

总结：

Settings的主Activity实质实现是在SettingsHomepageActivity.java内；
Settings的主界面设置item的显示是在fragment上，fragment为TopLevelSettings.java，加载显示的布局为top_level_settings.xml；
Settings主界面设置项item的加载显示主要分为两部分，一部分是xml定义的静态加载，xml为top_level_settings.xml；一部分是DashboardCategory来获取动态加载；
每个设置项item均为一个preference，通过xml定义加载时，必须要有一个controller，可以是在xml中定义"settings:controller"属性声明，名称必须与类的包名路径相同；也可直接在相关fragment中实现createPreferenceControllers()方法去调用构造相关controller。此二者存其一即可。
xml中配置preference时，必须定义”android:key“属性；

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