原因出在这个方法：[self.clientSocket readDataWithTimeout:-1 tag:0];

在连接成功的代理中：

//连接成功

-(void)socket:(GCDAsyncSocket*)sockdidConnectToHost:(NSString*)hostport:(uint16_t)port {

    NSLog(@"--连接成功--");

//必须加这个方法

    [self.clientSocket readDataWithTimeout:-1 tag:0];

}

在收到消息的代理中：

//收到的消息
-(void)socket:(GCDAsyncSocket*)sockdidReadData:(NSData*)datawithTag:(long)tag {

//也必须调用这个方法

    [self.clientSocket readDataWithTimeout:-1 tag:0];

//数据格式转换

    NSString*recvStr;

    if(data) {

        recvStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

    }

    NSLog(@"%@",recvStr);

}

完整的代码

#import <GCDAsyncSocket.h>

@interface MYSocketHelper () < GCDAsyncSocketDelegate>

@property (nonatomic, strong) GCDAsyncSocket *clientSocket;

@end

-(void)asynSocketInit {

    self.clientSocket = [[GCDAsyncSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_global_queue(0, 0)];

    NSError*err =nil;

    if (![self.clientSocket connectToHost:@"127.0.0.1" onPort: 60000 error:&err])   {

        NSLog(@"I goofed: %@", err);

    } else {

        [self.clientSocket writeData:[@"xxxx" dataUsingEncoding:NSUTF8StringEncoding] withTimeout:-1 tag:0];

    }

}

-(void)socket:(GCDAsyncSocket*)sockdidConnectToHost:(NSString*)hostport:(uint16_t)port {

    NSLog(@"--连接成功--");

    [self.clientSocket readDataWithTimeout:-1 tag:0];

}

-(void)socket:(GCDAsyncSocket*)sockdidReadData:(NSData*)datawithTag:(long)tag {

    [self.clientSocket readDataWithTimeout:-1 tag:0];

    NSString*recvStr;

    if(data) {

        recvStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

    }

    NSLog(@"%@",recvStr);

}

- (void)socket:(GCDAsyncSocket*)sockdidReadPartialDataOfLength:(NSUInteger)partialLengthtag:(long)tag {

}

-(void)socketDidDisconnect:(GCDAsyncSocket *)sock withError:(NSError *)err {

}

自测的话可以下载一个ssokit，模拟了socket服务端，能收发消息

地址：127.0.0.1本机的地址，端口范围 1024~65535。