Audio系列之通用的音量设置函数setStreamVolume（）

系统设置界面中就是使用AudioManager.setStreamVolume（），

说下比较难理解的flag参数在AudioManager在handlerKeyDown()中设置了两个flags,分别是FLAG_SHOW_UI和FLAG_VIBRATE.从字面上可知,前者告诉AudioService需要弹出一个音量控制面板,后者可能,只是可能是设置在为0时震动一下.而设置了FLAG_PLAY_SOUND是松开音量键时有个提示音.

源码：

/**
     * Sets the volume index for a particular stream.
     * <p>This method has no effect if the device implements a fixed volume policy
     * as indicated by {@link #isVolumeFixed()}.
     * <p>From N onward, volume adjustments that would toggle Do Not Disturb are not allowed unless
     * the app has been granted Do Not Disturb Access.
     * See {@link NotificationManager#isNotificationPolicyAccessGranted()}.
     * @param streamType The stream whose volume index should be set.
     * @param index The volume index to set. See
     *            {@link #getStreamMaxVolume(int)} for the largest valid value.
     * @param flags One or more flags.
     * @see #getStreamMaxVolume(int)