Android 10 Settings应用 整体流程

整体效果图
代码路径
packages/apps/Settingsres/layout/settings_homepage_container.xml
packages/apps/Settingssrc/com/android/settings/homepage/SettingsHomepageActivity.java
一、Settings应用主界面加载
1、从清单文件AndroidManifest.xml可以发现targetActivity属性，实质应是SettingsHomepageActivity.java。Settings应用UI布局主要是在SettingsHomepageActivity中加载的

2、在SettingsHomepageActivity.java文件中onCreate()方法中，我们可以看出是有两部分组成：1、头部搜索框。2、一级菜单选项

@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 , toolbar, SettingsEnums.SETTINGS_HOMEPAGE);

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

    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:，一级菜单选项滑动主要是采用NestedScrollView控件。顶部搜索框则采用AppBarLayout控件

主界面布局中主要包含三部分：两个frameLayout，一个顶部快捷搜索栏。其中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。主界面加载流程，所以主要看main_content。
回到onCreate()方法：TopLevelSettings主要是一级菜单的布局加载

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

启动TopLevelSettings的fragment，此fragments主要继承于DashboardFragment.java，先来看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);
    }

可以看到构造方法中仅设置了个标志位，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，此方法主要是完成mPreferenceControllers的加载。
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();
    }
}

第一次进入时，icicle为null，具体应该看引用的父类的onCreate()方法，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) {
    refreshAllPreferences(getLogTag());
}

调用refreshAllPreferences()：

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);
}

可以看到此方法主要是用来加载显示的preference items，主要分为两部分，一个是静态xml定义的prefs(调用displayResourceTiles()方法)，另一部分是从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：

    private void displayResourceTiles() {
        final int resId = getPreferenceScreenResId();
        if (resId <= 0) {
            return;
        }
        addPreferencesFromResource(resId);
        final PreferenceScreen screen = getPreferenceScreen();
        screen.setOnExpandButtonClickListener(this);
        mPreferenceControllers.values().stream().flatMap(Collection::stream).forEach(
                controller -> controller.displayPreference(screen));

首先调用getPreferenceScreenResId()方法获取所要加载的xml的ID：

@Override
    protected abstract int getPreferenceScreenResId();

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，其内主要配置的是一些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。以网络和互联网菜单项为例，xml配置如下：