基于Android Q 修改默认音量等级

在之前的一些android版本中，修改默认音量是修改：

path：frameworks\base\media\java\android\media\AudioService.java

    /// M: modify the default stream volume @{
    public static int[] DEFAULT_STREAM_VOLUME = new int[] {
        4,   // STREAM_VOICE_CALL
        8,  // STREAM_SYSTEM
        8,   // STREAM_RING
        8,   // STREAM_MUSIC
        8,   // STREAM_ALARM
        8,   // STREAM_NOTIFICATION
        8,   // STREAM_BLUETOOTH_SCO
        8,  // STREAM_SYSTEM_ENFORCED
        8,  // STREAM_DTMF
        8,  // STREAM_TTS
        8  // STREAM_ACCESSIBILITY
    };
    /// @}

当然此文件中也定义了Volume的最大值和最小值：

   /** Maximum volume index values for audio streams */
    /// M: Modify the max stream volume @{
    protected static int[] MAX_STREAM_VOLUME = new int[] {
        7,   // STREAM_VOICE_CALL
        15,  // STREAM_SYSTEM
        15,  // STREAM_RING
        15,  // STREAM_MUSIC
        15,  // STREAM_ALARM
        15,  // STREAM_NOTIFICATION
        15,  // STREAM_BLUETOOTH_SCO
        15,  // STREAM_SYSTEM_ENFORCED
        15,  // STREAM_DTMF
        15,  // STREAM_TTS
        15   // STREAM_ACCESSIBILITY
    };

    /** Minimum volume index values for audio streams */
    protected static int[] MIN_STREAM_VOLUME = new int[] {
        1,  // STREAM_VOICE_CALL
        0,  // STREAM_SYSTEM
        0,  // STREAM_RING
        0,  // STREAM_MUSIC
        1,  // STREAM_ALARM
        0,  // STREAM_NOTIFICATION
        0,  // STREAM_BLUETOOTH_SCO
        0,  // STREAM_SYSTEM_ENFORCED
        0,  // STREAM_DTMF
        0,  // STREAM_TTS
        1   // STREAM_ACCESSIBILITY
    };

OK  回归主题，在android Q版本中DEFAULT_STREAM_VOLUME数组的定义是在AudioSystem.java文件中，但是修改这个数组中的值发现还是无法正确处理为自己想要的默认值。

发现初始化默认值是在AudioService.java的AudioService()方法中：

        int maxCallVolume = SystemProperties.getInt("ro.config.vc_call_vol_steps", -1);
        if (maxCallVolume != -1) {
            MAX_STREAM_VOLUME[AudioSystem.STREAM_VOICE_CALL] = maxCallVolume;
        }

        int defaultCallVolume = SystemProperties.getInt("ro.config.vc_call_vol_default", -1);
        if (defaultCallVolume != -1 &&
                defaultCallVolume <= MAX_STREAM_VOLUME[AudioSystem.STREAM_VOICE_CALL] &&
                defaultCallVolume >= MIN_STREAM_VOLUME[AudioSystem.STREAM_VOICE_CALL]) {
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_VOICE_CALL] = defaultCallVolume;
        } else {
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_VOICE_CALL] =
                    (maxCallVolume * 3) / 4;
        }

        int maxMusicVolume = SystemProperties.getInt("ro.config.media_vol_steps", -1);
        if (maxMusicVolume != -1) {
            MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] = maxMusicVolume;
        }

        int defaultMusicVolume = SystemProperties.getInt("ro.config.media_vol_default", -1);
        if (defaultMusicVolume != -1 &&
                defaultMusicVolume <= MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] &&
                defaultMusicVolume >= MIN_STREAM_VOLUME[AudioSystem.STREAM_MUSIC]) {
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] = defaultMusicVolume;
        } else {
            if (isPlatformTelevision()) {
                AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] =
                        MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] / 4;
            } else {
                AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] =
                        MAX_STREAM_VOLUME[AudioSystem.STREAM_MUSIC] / 3;
            }
        }

        int maxAlarmVolume = SystemProperties.getInt("ro.config.alarm_vol_steps", -1);
        if (maxAlarmVolume != -1) {
            MAX_STREAM_VOLUME[AudioSystem.STREAM_ALARM] = maxAlarmVolume;
        }

        int defaultAlarmVolume = SystemProperties.getInt("ro.config.alarm_vol_default", -1);
        if (defaultAlarmVolume != -1 &&
                defaultAlarmVolume <= MAX_STREAM_VOLUME[AudioSystem.STREAM_ALARM]) {
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_ALARM] = defaultAlarmVolume;
        } else {
            // Default is 6 out of 7 (default maximum), so scale accordingly.
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_ALARM] =
                        6 * MAX_STREAM_VOLUME[AudioSystem.STREAM_ALARM] / 7;
        }

        int maxSystemVolume = SystemProperties.getInt("ro.config.system_vol_steps", -1);
        if (maxSystemVolume != -1) {
            MAX_STREAM_VOLUME[AudioSystem.STREAM_SYSTEM] = maxSystemVolume;
        }

        int defaultSystemVolume = SystemProperties.getInt("ro.config.system_vol_default", -1);
        if (defaultSystemVolume != -1 &&
                defaultSystemVolume <= MAX_STREAM_VOLUME[AudioSystem.STREAM_SYSTEM]) {
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_SYSTEM] = defaultSystemVolume;
        } else {
            // Default is to use maximum.
            AudioSystem.DEFAULT_STREAM_VOLUME[AudioSystem.STREAM_SYSTEM] =
                        MAX_STREAM_VOLUME[AudioSystem.STREAM_SYSTEM];
        }

发现这些初始化的值都是由一些ro.config.属性控制的，所以要修改默认音量大小，可以直接客制化ro.config.这些属性值就OK。