你可以像这样检测它。无需私有API

static void _callback(CFNotificationCenterRef center, void *observer, CFStringRef name, const void *object, CFDictionaryRef userInfo)
{
    if ([(__bridge NSString*)name isEqualToString:@"com.apple.mobile.lockdown.host_attached"])
    {
        NSLog(@"USB connected");
    }
    else if ([(__bridge NSString*)name isEqualToString:@"com.apple.mobile.lockdown.host_detached"])
    {
        NSLog(@"USB disconnected");
    }
}

CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, _callback, CFSTR("com.apple.mobile.lockdown.host_attached"), NULL, CFNotificationSuspensionBehaviorDeliverImmediately);
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, _callback, CFSTR("com.apple.mobile.lockdown.host_detached"), NULL, CFNotificationSuspensionBehaviorDeliverImmediately);