GCDAsyncUdpSocket用来和硬件进行广播信息交流，很简单，很好用。
添加GCDAsyncUdpSocket工具库，出现以下错误：
------------------------------------------------------------------------
Undefined symbols for architecture arm64:
"_OBJC_CLASS_$_GCDAsyncUdpSocket", referenced from:
objc-class-ref in MessageManager.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
------------------------------------------------------------------------
1，首先检查所需的框架是否导入完全，CFNetwork.framework 、 Security.framework
2，如果是手动拖入GCD包，查看project>>build phases>>compile sources里面是否含有GCDAsyncSocket.m和GCDAsyncUdpSocket.m两个编译项，如没有，添加上去
3，如果是pods导入GCD包，点击pods工程，查看如下选项
如你出现和上图一样的情况，赶紧添加GCDAsyncSocket.m和GCDAsyncUdpSocket.m两个编译项，编译成功
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