客户端我们使用iPhone应用程序，画面比较简单。点击发送按钮，给服务器发送一些字符串过去。点击接收按钮就会从服务器读取一些字符串，并且显示在画面上。
有关客户端应用的UI部分不再介绍了，我们直接看代码部分，Socket客户端可以采用CFStream或NSStream实现，CFStream 实现方式与服务器端基本一样。为了给读者介绍更多的知识，本例我们采用NSStream实现。NSStream实现采用Objective-C语言，一些 面向对象的类。
下面我们看看客户端视图控制器ViewController.h
#import <CoreFoundation/CoreFoundation.h>#include <sys/socket.h>#include <netinet/in.h>#define PORT 9000@interface ViewController : UIViewController<NSStreamDelegate>{int flag ; //操作标志 0为发送 1为接收}@property (nonatomic, retain) NSInputStream *inputStream;@property (nonatomic, retain) NSOutputStream *outputStream;@property (weak, nonatomic) IBOutlet UILabel *message;- (IBAction)sendData:(id)sender;- (IBAction)receiveData:(id)sender;@end
定义属性inputStream和outputStream，它们输入流NSInputStream和输出流NSOutputStream类。它们与服务器CFStream实现中的输入流CFReadStreamRef和输出流CFWriteStreamRef对应的。
视图控制器ViewController.m的初始化网络方法initNetworkCommunication代码：
- (void)initNetworkCommunication{CFReadStreamRef readStream;CFWriteStreamRef writeStream;CFStreamCreatePairWithSocketToHost(NULL,(CFStringRef)@”192.168.1.103″, PORT, &readStream, &writeStream); ①_inputStream = (__bridge_transfer NSInputStream *)readStream; ②_outputStream = (__bridge_transfer NSOutputStream*)writeStream; ③[_inputStream setDelegate:self]; ④[_outputStream setDelegate:self]; ⑤[_inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop]forMode:NSDefaultRunLoopMode]; ⑥[_outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop]forMode:NSDefaultRunLoopMode]; ⑦[_inputStream open]; ⑧[_outputStream open]; ⑨}
点击发送和接收按钮触发的方法如下：
/* 点击发送按钮 */- (IBAction)sendData:(id)sender {flag = 0;[self initNetworkCommunication];}/* 点击接收按钮 */- (IBAction)receiveData:(id)sender {flag = 1;[self initNetworkCommunication];}
它们都调用initNetworkCommunication方法，并设置操作标识flag，如果flag为0发送数据，flag为1接收数据。
流的状态的变化触发很多事件，并回调NSStreamDelegate协议中定义的方法stream:handleEvent:，其代码如下：
-(void)stream:(NSStream *)theStream handleEvent:(NSStreamEvent)streamEvent {NSString *event;switch (streamEvent) {case NSStreamEventNone:event = @”NSStreamEventNone”;break;case NSStreamEventOpenCompleted:event = @”NSStreamEventOpenCompleted”;break;case NSStreamEventHasBytesAvailable:event = @”NSStreamEventHasBytesAvailable”;if (flag ==1 && theStream == _inputStream) {NSMutableData *input = [[NSMutableData alloc] init];uint8_t buffer[1024]; ①int len;while([_inputStream hasBytesAvailable]) ②{len = [_inputStream read:buffer maxLength:sizeof(buffer)]; ③if (len > 0){[input appendBytes:buffer length:len];}}NSString *resultstring = [[NSString alloc]initWithData:input encoding:NSUTF8StringEncoding];NSLog(@”接收:%@”,resultstring);_message.text = resultstring;}break;case NSStreamEventHasSpaceAvailable:event = @”NSStreamEventHasSpaceAvailable”;if (flag ==0 && theStream == _outputStream) {//输出UInt8 buff[] = ”Hello Server!”; ④[_outputStream write:buff maxLength: strlen((const char*)buff)+1]; ⑤//关闭输出流[_outputStream close];}break;case NSStreamEventErrorOccurred:event = @”NSStreamEventErrorOccurred”;[self close]; ⑥break;case NSStreamEventEndEncountered:event = @”NSStreamEventEndEncountered”;NSLog(@”Error:%d:%@”,[[theStream streamError] code],[[theStream streamError] localizedDescription]);break;default:[self close]; ⑦event = @”Unknown”;break;}NSLog(@”event??%@”,event);}
在读取数据分支（NSStreamEventHasBytesAvailable）中，代码第①行为读取数据准备缓冲区，本例中设置的是1024个字节，这个大小会对流的读取有很多的影响。第②行代码使用hasBytesAvailable方法判断是否流有数据可以读，如果有可读数据就进行循环读取。第③行代码使用流的read:maxLength:方法读取数据到缓冲区，第1个参数是缓冲区对象buffer，第2个参数是读取的缓冲区的字节长度。
在写入数据分支（NSStreamEventHasSpaceAvailable）中，代码第④行是要写入的数据，第⑤行代码 [_outputStream write:buff maxLength: strlen((const char*)buff)+1]是写如数据方 法。
第⑥和第⑦行代码[self close]调用close方法关闭，close方法代码如下：
-(void)close{[_outputStream close];[_outputStream removeFromRunLoop:[NSRunLoop currentRunLoop]forMode:NSDefaultRunLoopMode];[_outputStream setDelegate:nil];[_inputStream close];[_inputStream removeFromRunLoop:[NSRunLoop currentRunLoop]forMode:NSDefaultRunLoopMode];[_inputStream setDelegate:nil];}
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