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-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.
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:
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 controllersFromCode =
createPreferenceControllers(context);
// Load preference controllers from xml definition
final List controllersFromXml = PreferenceControllerListHelper
.getPreferenceControllersFromXml(context, getPreferenceScreenResId());
// Filter xml-based controllers in case a similar controller is created from code already.
final List 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：
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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