android音量调节（四）android10 设置模块音量设置源码实现

android 修改音量除了实体按键，还有在设置模块中，有专门的音量模块可以滑动滑动条（seekbar）来控制音量（界面如下图所示）。接下来我们看下源码中怎么拖拽设置音量的。

该界面布局界面加载fragment的路径：

packages/apps/Settings/res/xml/sound_settings.xml

packages/apps/Settings/src/com/android/settings/notification/SoundSettings.java

<!-- Media volume -->
    <com.android.settings.notification.VolumeSeekBarPreference
        android:key="media_volume"
        android:icon="@drawable/ic_media_stream"
        android:title="@string/media_volume_option_title"
        android:order="-180"
        settings:controller="com.android.settings.notification.MediaVolumePreferenceController"/>

    <!-- Call volume -->
    <com.android.settings.notification.VolumeSeekBarPreference
        android:key="call_volume"
        android:icon="@drawable/ic_local_phone_24_lib"
        android:title="@string/call_volume_option_title"
        android:order="-170"
        settings:controller="com.android.settings.notification.CallVolumePreferenceController"/>
    <!-- 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"/>


    <!-- Alarm volume -->
    <com.android.settings.notification.VolumeSeekBarPreference
        android:key="alarm_volume"
        android:icon="@*android:drawable/ic_audio_alarm"
        android:title="@string/alarm_volume_option_title"
        android:order="-150"
        settings:controller="com.android.settings.notification.AlarmVolumePreferenceController"/>

 以上是图一对应的布局（其他音量的不再此讨论，逻辑几乎是一样的）

我们看到每个布局都对应一个controller，我们以闹钟为例

1. 布局类是VolumeSeekBarPreference，逻辑类是AlarmVolumePreference。

public class AlarmVolumePreferenceController extends VolumeSeekBarPreferenceController {

    private static final String KEY_ALARM_VOLUME = "alarm_volume";

    public AlarmVolumePreferenceController(Context context) {
        super(context, KEY_ALARM_VOLUME);
    }

    @Override
    public int getAvailabilityStatus() {
        return mContext.getResources().getBoolean(R.bool.config_show_alarm_volume)
                && !mHelper.isSingleVolume() ? AVAILABLE : UNSUPPORTED_ON_DEVICE;
    }

    @Override
    public boolean isSliceable() {
        return TextUtils.equals(getPreferenceKey(), "alarm_volume");
    }

    @Override
    public boolean useDynamicSliceSummary() {
        return true;
    }

    @Override
    public String getPreferenceKey() {
        return KEY_ALARM_VOLUME;
    }

    @Override
    public int getAudioStream() {
        return AudioManager.STREAM_ALARM;
    }

    @Override
    public int getMuteIcon() {