記一次設定音量調節的原始碼分析:

調節音量一般在設定裡面,於是找到了設定頁面的原始碼:SettingsActivity

  @VisibleForTesting
    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 {
            // Show search icon as up affordance if we are displaying the main Dashboard
            mInitialTitleResId = R.string.dashboard_title;
            switchToFragment(TopLevelSettings.class.getName(), null /* args 
 
*/, false,
                    mInitialTitleResId, mInitialTitle);
        }
    }

然後進入到TopLevelSettings

 public static final BaseSearchIndexProvider SEARCH_INDEX_DATA_PROVIDER =
            new BaseSearchIndexProvider(R.xml.top_level_settings) {

                @Override
                protected
 
 boolean isPageSearchEnabled(Context context) {
                    // Never searchable, all entries in this page are already indexed elsewhere.
                    return false;
                }
            };

再進入top_level_settings

<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"/>

進入SoundSettings

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

進入sound_settings

  <!-- Ring volume -->
    <com.android.settings.notification.VolumeSeekBarPreference
        android:key="ring_volume"
        android:icon="@drawable/ic_notifications"
        android:title="@string/ring_volume_option_title"
        android:order="-160"
        settings:controller="com.android.settings.notification.RingVolumePreferenceController"/>

進入RingVolumePreferenceController

    private void updateRingerMode() {
        final int ringerMode = mHelper.getRingerModeInternal();
        if (mRingerMode == ringerMode) return;
        mRingerMode = ringerMode;
        updatePreferenceIcon();
    }

進入AudioHelper

    public int getRingerModeInternal() {
        return mAudioManager.getRingerModeInternal();
    }

進入frameworks/base/media/java/android/media/AudioManager

    @UnsupportedAppUsage
    public int getRingerModeInternal() {
        try {
            return getService().getRingerModeInternal();
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

進入getService方法

 @UnsupportedAppUsage
    private static IAudioService getService()
    {
        if (sService != null) {
            return sService;
        }
        IBinder b = ServiceManager.getService(Context.AUDIO_SERVICE);
        sService = IAudioService.Stub.asInterface(b);
        return sService;
    }

進入frameworks/base/media/java/android/media/IAudioService.aidl

  int getRingerModeInternal();

進入frameworks/base/services/core/java/com/android/servicer/audio/AudioService

public class AudioService extends IAudioService.Stub
        implements AccessibilityManager.TouchExplorationStateChangeListener,
            AccessibilityManager.AccessibilityServicesStateChangeListener {

進入方法getRingerModeInternal

  @Override
    public int getRingerModeInternal() {
        synchronized(mSettingsLock) {
            return mRingerMode;
        }
    }

可以看到音量的調節是有這個mRingerMode來控制

   private void readPersistedSettings() {
        if (!mSystemServer.isPrivileged()) {
            return;
        }
        final ContentResolver cr = mContentResolver;

        int ringerModeFromSettings =
                Settings.Global.getInt(
                        cr, Settings.Global.MODE_RINGER, AudioManager.RINGER_MODE_NORMAL);
        int ringerMode = ringerModeFromSettings;
        // sanity check in case the settings are restored from a device with incompatible
        // ringer modes
        if (!isValidRingerMode(ringerMode)) {
            ringerMode = AudioManager.RINGER_MODE_NORMAL;
        }
        if ((ringerMode == AudioManager.RINGER_MODE_VIBRATE) && !mHasVibrator) {
            ringerMode = AudioManager.RINGER_MODE_SILENT;
        }
        if (ringerMode != ringerModeFromSettings) {
            Settings.Global.putInt(cr, Settings.Global.MODE_RINGER, ringerMode);
        }
        if (mUseFixedVolume || mIsSingleVolume) {
            ringerMode = AudioManager.RINGER_MODE_NORMAL;
        }
        synchronized(mSettingsLock) {
            mRingerMode = ringerMode;
            if (mRingerModeExternal == -1) {
                mRingerModeExternal = mRingerMode;
            }