在友盟里注册App时需要获取UDID，但友盟只给出OC版本。
以下是自己写的Swift版本：

class func GetUDID() {
    
    let deviceSelector = Selector("openUDIDString")
    
    guard
        let cls = NSClassFromString("UMANUtil"),
        let deviceID = (cls as? NSObjectProtocol)?.performSelector(deviceSelector).takeUnretainedValue() as? String,
        let jsonData = try? NSJSONSerialization.dataWithJSONObject(["oid": deviceID], options: NSJSONWritingOptions.PrettyPrinted)
    else {
        NSLog("UMengUDIDGetter: Can't get UDID.")
        return
    }
    
    NSLog("%@", String(data: jsonData, encoding: NSUTF8StringEncoding)!)
}