Settings一级界面显示分析_settingshomepageactivity-优快云博客

Settings是系统提供各种设置的一个应用，源码位于packages/apps/Settings，平板上界面如下：

从上面抓取的布局来看，整体布局是RecyclerView+Fragment。

主要类

SettingsHomepageActivity.java：主界面，采用RecyclerView+Fragment结构
settings_homepage_container.xml：主界面布局文件
TopLevelSettings.java：主界面中Fragment
DashboardFragment.java：Settings中一个fragment基类，用来显示Prefrence列表
top_level_settings.xml：主界面Prefrence布局文件
SubSettingLauncher.java：SubSettings启动类，点击Prefrence是启动SubSettings，SubSettings是一个Activity
SubSettings.java/SettingsActivity.java：展示Prefrence对应的fragment

创建主界面Activity

Mainfest中设置的LauncherActivity为Settings，这个是一个别名，实际指向的是SettingsHomepageActivity

// Settings\AndroidManifest.xml
<activity-alias android:name="Settings"
        android:label="@string/settings_label_launcher"
        android:taskAffinity="com.android.settings.root"
        android:launchMode="singleTask"
        android:exported="true"
        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>

SettingsHomepageActivity extends FragmentActivity，onCreate()中主要进行加载布局，创建Fragment，布局文件settings_homepage_container.xml和上面抓取的布局是可以对上的

// Settings\src\com\android\settings\homepage\SettingsHomepageActivity.java
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // 1. 是否嵌入显示Activity
    mIsEmbeddingActivityEnabled = ActivityEmbeddingUtils.isEmbeddingActivityEnabled(this);
  
    // 2. 设置布局文件
    setContentView(R.layout.settings_homepage_container);
   
    // 3. 设置主界面背景、appbar高度、搜索栏等
    updateAppBarMinHeight();
    initHomepageContainer();
    updateHomepageAppBar();
    updateHomepageBackground();
    initSearchBarView();

    // 4. 不是低内存设备，显示建议条目
    if (!getSystemService(ActivityManager.class).isLowRamDevice()) {
        initAvatarView();
        showSuggestionFragment(scrollNeeded);
        
    }

    // 5.创建fragment
    mMainFragment = showFragment(() -> {
        final TopLevelSettings fragment = new TopLevelSettings();
        fragment.getArguments().putString(SettingsActivity.EXTRA_FRAGMENT_ARG_KEY,
                highlightMenuKey);
        return fragment;
    }, R.id.main_content);
}

创建主界面PrefrenceFragment

TopLevelSettings extends DashboardFragment，DashboardFragment是Settings中一个fragment基类，用来显示Prefrence列表。

TopLevelSettings主要是实现DashboardFragment的一些方法，如设置布局文件、左侧prefrence点击事件等，部分代码如下：

// Settings\src\com\android\settings\homepage\TopLevelSettings.java
// 设置prefrence布局
protected int getPreferenceScreenResId() {
    return R.xml.top_level_settings;
}
// onAttach
public void onAttach(Context context) {
    super.onAttach(context);
    HighlightableMenu.fromXml(context, getPreferenceScreenResId());
    use(SupportPreferenceController.class).setActivity(getActivity());
}
// 左侧prefrence点击事件
public boolean onPreferenceTreeClick(Preference preference) {
    if (isDuplicateClick(preference)) {
        return true;
    }
    ActivityEmbeddingRulesController.registerSubSettingsPairRule(getContext(),
            true /* clearTop */);
    setHighlightPreferenceKey(preference.getKey());
    return super.onPreferenceTreeClick(preference);
}
// 创建fragment
public boolean onPreferenceStartFragment(PreferenceFragmentCompat caller, Preference pref) {
    new SubSettingLauncher(getActivity())
            .setDestination(pref.getFragment())
            .setArguments(pref.getExtras())
            .setSourceMetricsCategory(caller instanceof Instrumentable
                    ? ((Instrumentable) caller).getMetricsCategory()
                    : Instrumentable.METRICS_CATEGORY_UNKNOWN)
            .setTitleRes(-1)
            .setIsSecondLayerPage(true)
            .launch();
    return true;
}

接下来，我们具体来看DashboardFragment，DashboardFragment继承层次比较多，具体如下，最终基类是PreferenceFragment，说明采用的Prefrence组件。Prefrence组件用法可以参考最后面博客。

TopLevelSettings --> DashboardFragment --> SettingsPreferenceFragment --> InstrumentedPreferenceFragment --> ObservablePreferenceFragment --> PreferenceFragmentCompat

onPreferenceTreeClick()回调逻辑：在InstrumentedPreferenceFragment给所有的Preference设置了点击事件，点击后会回调
onPreferenceTreeClick()，所以可以在该方法中判断相应的Prefrence进行对应的处理。

// Settings\src\com\android\settings\core\InstrumentedPreferenceFragment.java
public void onStart() {
    super.onStart();
    // Override the OnPreferenceTreeClickListener in super.onStart() to inject jank detection.
    getPreferenceManager().setOnPreferenceTreeClickListener((preference) -> {
        if (preference instanceof SwitchPreference) {
            SettingsJankMonitor.detectSwitchPreferenceClickJank(
                    getListView(), (SwitchPreference) preference);
        }
        return onPreferenceTreeClick(preference);
    });
}

getPreferenceScreenResId()逻辑：将getPreferenceScreenResId()返回的布局文件设置给了PreferenceFragment。所以，R.xml.top_level_settings就是主界面布局文件

// Settings\src\com\android\settings\core\InstrumentedPreferenceFragment.java
public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
    final int resId = getPreferenceScreenResId();
    if (resId > 0) {
        addPreferencesFromResource(resId);
    }
}

onPreferenceStartFragment()逻辑：onPreferenceStartFragment是PreferenceFragmentCompat.OnPreferenceStartFragmentCallback接口的方法，TopLevelSettings implements PreferenceFragmentCompat.OnPreferenceStartFragmentCallback，但好像没有看到registerOnPreferenceStartFragmentCallback，其实这个代码是在PreferenceFragmentCompat中，在Preference点击的时候，执行了onPreferenceStartFragment

// androidx/preference/preference/src/main/java/androidx/preference/PreferenceFragmentCompat.java
public boolean onPreferenceTreeClick(@NonNull Preference preference) {
    if (preference.getFragment() != null) {
        // 在Preference点击的时候，执行了onPreferenceStartFragment
        boolean handled = false;
        if (getCallbackFragment() instanceof OnPreferenceStartFragmentCallback) {
            handled = ((OnPreferenceStartFragmentCallback) getCallbackFragment())
                    .onPreferenceStartFragment(this, preference);
        }
        

        Fragment callbackFragment = this;
        while (!handled && callbackFragment != null) {
            if (callbackFragment instanceof OnPreferenceStartFragmentCallback) {
                handled = ((OnPreferenceStartFragmentCallback) callbackFragment)
                        .onPreferenceStartFragment(this, preference);
            }
            callbackFragment = callbackFragment.getParentFragment();
        }
        if (!handled && getContext() instanceof OnPreferenceStartFragmentCallback) {
            handled = ((OnPreferenceStartFragmentCallback) getContext())
                    .onPreferenceStartFragment(this, preference);
        }
        ...
        return true;
    }
    return false;
}

至此，我们已经清楚主界面左侧Preference列表的显示流程，但是右侧的Fragment的怎么显示出来的，我们还不知道。我们想一下，如果我们来用Preference+Fragment来实现左右双列显示，应该也是可以做的，比如两个FrameLayout，一个显示Preference列表Fragment，一个显示对应Preference条目Fragment

启动SubSettings

上面我们知道点击左侧preference条目时会执行onPreferenceStartFragment，接下来具体看代码

// Settings\src\com\android\settings\homepage\TopLevelSettings.java
// 创建fragment
public boolean onPreferenceStartFragment(PreferenceFragmentCompat caller, Preference pref) {
    new SubSettingLauncher(getActivity())
            .setDestination(pref.getFragment())
            .setArguments(pref.getExtras())
            .setSourceMetricsCategory(caller instanceof Instrumentable
                    ? ((Instrumentable) caller).getMetricsCategory()
                    : Instrumentable.METRICS_CATEGORY_UNKNOWN)
            .setTitleRes(-1)
            .setIsSecondLayerPage(true)
            .launch();
    return true;
}

SubSettingLauncher中将传过来的fragment等信息设置给intent，然后通过startActivity启动SubSettings

// Settings\src\com\android\settings\core\SubSettingLauncher.java
public class SubSettingLauncher {
    // 内部参数类
    private final LaunchRequest mLaunchRequest;
    // launch()通过startActivity启动SubSettings
    public void launch() {
        final Intent intent = toIntent();
        boolean launchAsUser = mLaunchRequest.mUserHandle != null
                && mLaunchRequest.mUserHandle.getIdentifier() != UserHandle.myUserId();
        boolean launchForResult = mLaunchRequest.mResultListener != null;
        if (launchAsUser && launchForResult) {
            launchForResultAsUser(intent, mLaunchRequest.mUserHandle,
                    mLaunchRequest.mResultListener, mLaunchRequest.mRequestCode);
        } else if (launchAsUser && !launchForResult) {
            launchAsUser(intent, mLaunchRequest.mUserHandle);
        } else if (!launchAsUser && launchForResult) {
            launchForResult(mLaunchRequest.mResultListener, intent, mLaunchRequest.mRequestCode);
        } else {
            launch(intent);
        }
    }
    // 生成intent
    public Intent toIntent() {
        final Intent intent = new Intent(Intent.ACTION_MAIN);
        copyExtras(intent);
        intent.setClass(mContext, SubSettings.class); // 注意这里，启动了SubSettings
        if (TextUtils.isEmpty(mLaunchRequest.mDestinationName)) {
            throw new IllegalArgumentException("Destination fragment must be set");
        }
        intent.putExtra(SettingsActivity.EXTRA_SHOW_FRAGMENT, mLaunchRequest.mDestinationName);
        return intent;
    }
    // 启动Activity
    void launchAsUser(Intent intent, UserHandle userHandle) {
        mContext.startActivityAsUser(intent, userHandle);
    }
}

SubSettings extends SettingsActivity，在onCreate()中拿到传过来的fragment className，通过反射的创建了fragment，然后进行了显示

// Settings\src\com\android\settings\SettingsActivity.java
protected void onCreate(Bundle savedState) {
    super.onCreate(savedState);
    Log.d(LOG_TAG, "Starting onCreate");
    createUiFromIntent(savedState, intent);
}
protected void createUiFromIntent(Bundle savedState, Intent intent) {
    ...
    // 从intent中拿到fragment className
    final String initialFragmentName = getInitialFragmentName(intent);
    // 设置布局文件
    setContentView(R.layout.settings_main_prefs);
    getSupportFragmentManager().addOnBackStackChangedListener(this);
    if (savedState != null) {
        
    } else {
        // 默认进来走这里
        launchSettingFragment(initialFragmentName, intent);
    }
   ...
}

void launchSettingFragment(String initialFragmentName, Intent intent) {
    if (initialFragmentName != null) {
        setTitleFromIntent(intent);
        Bundle initialArguments = intent.getBundleExtra(EXTRA_SHOW_FRAGMENT_ARGUMENTS);
        switchToFragment(initialFragmentName, initialArguments, true,
                mInitialTitleResId, mInitialTitle);
    } else {
        mInitialTitleResId = R.string.dashboard_title;
        switchToFragment(TopLevelSettings.class.getName(), null /* args */, false,
                mInitialTitleResId, mInitialTitle);
    }
}

// 创建显示fragment
private void switchToFragment(String fragmentName, Bundle args, boolean validate,
        int titleResId, CharSequence title) {
    Log.d(LOG_TAG, "Switching to fragment " + fragmentName);
    
    // 通过反射的创建fragment
    Fragment f = Utils.getTargetFragment(this, fragmentName, args);
    if (f == null) {
        return;
    }
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.main_content, f);
    if (titleResId > 0) {
        transaction.setBreadCrumbTitle(titleResId);
    } else if (title != null) {
        transaction.setBreadCrumbTitle(title);
    }
    transaction.commitAllowingStateLoss();
    getSupportFragmentManager().executePendingTransactions();
}