• 首先需要安裝一個TCP&UDP測試工具
• 連線型別選擇UDP
• 目標IP 設定手機的IP， 埠8888 （這個埠在App端用來繫結）
• 指定埠， 是App向回發信息所需要的埠， 具體設定如下圖所示

接下來為減少程式碼的鍵入， 我直接使用CocoaAsyncSocket這個三方庫，作為中間媒介完成整個過程

{
      GCDAsyncUdpSocket *udpSocket; // 定義一個socket的物件 簽訂代理 GCDAsyncUdpSocketDelegate
}

麥 2017/7/20 17:05:40
    /*************** UDP ***********************/
 

    udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)];
    NSError *error = nil;
    // 繫結埠
    [udpSocket bindToPort:8888 error:&error];
    // 啟用廣播
    [udpSocket enableBroadcast:YES error:&error];

    if (error) {
        [SVProgressHUD showErrorWithStatus:@"啟用失敗"
 
];
    }else {
        NSLog(@"%@", [udpSocket localHost]);
        // 開始接收訊息
        [udpSocket beginReceiving:&error];

    }
    /*************** UDP ***********************/

#pragma mark - GCDAsyncUdpSocketDelegate
- (void)udpSocket:(GCDAsyncUdpSocket *)sock didReceiveData:(NSData *)data fromAddress:(NSData
 
 *)address withFilterContext:(nullable id)filterContext {

    NSLog(@"success");
    NSString *ip = [GCDAsyncUdpSocket hostFromAddress:address];
    NSString *s = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"收到響應 %@ %@", ip, s);
    [sock receiveOnce:nil];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        uint16_t port = 9999;
        [self sendBackToHost:ip port:port withMessage:s];
    });
}
- (void)sendBackToHost:(NSString *)ip port:(uint16_t)port withMessage:(NSString *)s{
    // 回一個 hello summerxx too
    char *str = "hello summerxx too" ;
    NSData *data = [NSData dataWithBytes:str length:strlen(str)];
    [udpSocket sendData:data toHost:ip port:port withTimeout:0.1 tag:200];
}