NSInputStream 和 NSOutputStream

对于 NSInputStream 和 NSOutputStream 一直没怎么搞清楚，今天抽一些时间在此记录一下！

NSInputStream 与 NSOutputStream 都继承于 NSStream, NSStream 是一个抽象的基类, 规定了Stream共有的一些行为…

什么是Stream

Stream翻译成为流，它是对我们读写文件的一个抽象。 你可以这样想象，当你读文件和写文件的时候，文件的内容就像水流一样哗哗的像你流过来或者流给别人，这样岂不是很爽。 而Stream就帮我们做了这样的事情， 实际上，它是把文件的内容，一小段一小段的读出或写入，来到达这样的效果

NSStream

NSStream 是Cocoa平台下对流这个概念的实现类， NSInputStream 和 NSOutputStream 则是它的两个子类，分别对应了读文件和写文件。

NSInputStream

NSInputStream 对应的是读文件，所以要记住它是要将文件的内容读到内存(你声明的一段buffer)里, 下面一段是测试代码

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- (void)doTestInputStream { NSString *path = @"/Users/usr/Desktop/stream.txt"; NSInputStream *readStream = [[NSInputStream alloc]initWithFileAtPath:path]; [readStream setDelegate:self]; [readStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes]; [readStream open]; //调用open开始读文件}- (void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode { switch (eventCode) { case NSStreamEventHasBytesAvailable:{ uint8_t buf[1024]; NSInputStream *reads = (NSInputStream *)aStream; NSInteger blength = [reads read:buf maxLength:sizeof(buf)]; //把流的数据放入buffer NSData *data = [NSData dataWithBytes:(void *)buf length:blength]; NSString *string = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"%@",string); } break; //错误和无事件处理 case NSStreamEventErrorOccurred:{ } break; case NSStreamEventNone: break; //打开完成 case NSStreamEventOpenCompleted: { NSLog(@"NSStreamEventOpenCompleted"); } break; default: break; }}@end

NSOutputStream

NSOutputStream 对应的是写文件，它是要将已存在的内存(buffer)里的数据写入文件, 下面同样一段是测试代码

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- (NSData *)dataWillWrite { static NSData *data = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ data = [NSData dataWithContentsOfFile:@"/Users/usr/Desktop/stream.txt"]; }); return data;}- (void)doTestOutputStream { NSString *path = @"/Users/usr/Desktop/stream-write.txt"; NSOutputStream *writeStream = [[NSOutputStream alloc] initToFileAtPath:path append:YES]; [writeStream setDelegate:self]; [writeStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes]; [writeStream open];}- (void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode { switch (eventCode) { case NSStreamEventHasSpaceAvailable: { NSInteger bufSize = 5; uint8_t buf[bufSize]; if (self.location + bufSize > [self dataWillWrite].length) { [[self dataWillWrite] getBytes:buf range:NSMakeRange(self.location, self.location + bufSize - [self dataWillWrite].length)]; } else { [[self dataWillWrite] getBytes:buf range:NSMakeRange(self.location, bufSize)]; } NSOutputStream *writeStream = (NSOutputStream *)aStream; [writeStream write:buf maxLength:sizeof(buf)]; //把buffer里的数据，写入文件 self.location += bufSize; if (self.location >= [[self dataWillWrite] length] ) { //写完后关闭流 [aStream close]; } } break; case NSStreamEventEndEncountered: { [aStream close]; } break; //错误和无事件处理 case NSStreamEventErrorOccurred:{ } break; case NSStreamEventNone: break; //打开完成 case NSStreamEventOpenCompleted: { NSLog(@"NSStreamEventOpenCompleted"); } break; default: break; }}

用途

NSInputStream 和 NSOutputStream 常用与网络传输中，比如要将一个很大的文件传送给服务器，那么NSInputStream这时候是很好的选择, 我们可以查看到 NSURLRequest 有一个属性叫HTTPBodyStream， 这时只要设置好一个NSInputStream的实例就可以了，最大的好处就是可以节省我们很多的内存。

另外要说明的是，NSInputStream 和 NSOutputStream其实是对 CoreFoundation 层对应的CFReadStreamRef 和 CFWriteStreamRef的高层抽象。在使用CFNetwork时，常常会使用到CFReadStreamRef 与 CFWriteStreamRef。 下面是一段相关代码

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// Keep a reference to self to use for controller callbacks // CFStreamClientContext ctx = {0, (__bridge void *)(self), NULL, NULL, NULL}; // Get callbacks for stream data, stream end, and any errors // CFOptionFlags registeredEvents = (kCFStreamEventHasBytesAvailable | kCFStreamEventEndEncountered | kCFStreamEventErrorOccurred); // Create a read-only socket // CFReadStreamRef readStream; CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (__bridge CFStringRef)host, (UInt32)port, &readStream, NULL); // Schedule the stream on the run loop to enable callbacks // if (CFReadStreamSetClient(readStream, registeredEvents, socketCallback, &ctx)) { CFReadStreamScheduleWithRunLoop(readStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes); } else { [self networkFailedWithErrorMessage:@"Failed to assign callback method"]; return; } // Open the stream for reading // if (CFReadStreamOpen(readStream) == NO) { [self networkFailedWithErrorMessage:@"Failed to open read stream"]; return; } CFErrorRef error = CFReadStreamCopyError(readStream); if (error != NULL) { if (CFErrorGetCode(error) != 0) { NSString * errorInfo = [NSString stringWithFormat:@"Failed to connect stream; error '%@' (code %ld)", (__bridge NSString*)CFErrorGetDomain(error), CFErrorGetCode(error)]; [self networkFailedWithErrorMessage:errorInfo]; } CFRelease(error); return; }