如何在代码中检查Airplay设备

Question

我正在使用自定义Airplay按钮进行播放。它工作正常

volumeView = [[MPVolumeView alloc] initWithFrame:CGRectZero];
[volumeView setShowsVolumeSlider:NO];
for (UIButton *button in volumeView.subviews) {
    if ([button isKindOfClass:[UIButton class]]) {
        airplayButton = button; // @property retain
        [airplayButton setImage:image forState:UIControlStateNormal];
        [airplayButton setImage:image forState:UIControlStateSelected];
        [airplayButton setImage:image forState:UIControlStateHighlighted];
        [airplayButton setBounds:CGRectMake(0, 0, iconSize, iconSize)];
        [airplayButton setBackgroundColor:[UIColor clearColor]];
    }
}

问题是：Airplay设备在苹果电视断开连接后显示。

如果没有可用的设备，我想在播放按钮时显示警告。

有没有办法查看可用的airplay设备？