NSInputStream 和 NSOutputStream

對於 NSInputStream 和 NSOutputStream 一直沒怎麼搞清楚，今天抽一些時間在此記錄一下！

NSInputStream 與 NSOutputStream 都繼承於 NSStream, NSStream 是一個抽象的基類, 規定了Stream共有的一些行爲…

什麼是Stream

Stream翻譯成爲流，它是對我們讀寫文件的一個抽象。 你可以這樣想象，當你讀文件和寫文件的時候，文件的內容就像水流一樣嘩嘩的 像你流過來或者流給別人，這樣豈不是很爽。 而Stream就幫我們做了這樣的事情， 實際上，它是把文件的內容，一小段一小段的讀出或 寫入，來到達這樣的效果

NSStream

NSStream 是Cocoa平臺下對流這個概念的實現類， NSInputStream 和 NSOutputStream 則是它的兩個子類，分別對應了讀文件和 寫文件。

NSInputStream

NSInputStream 對應的是讀文件，所以要記住它是要將文件的內容讀到內存(你聲明的一段buffer)裏, 下面一段是測試代碼

- (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]; //調用open開始讀文件 } - (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)]; //把流的數據放入buffer NSData *data = [NSData dataWithBytes:(void *)buf length:blength]; NSString *string = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"%@",string); } break; //錯誤和無事件處理 case NSStreamEventErrorOccurred:{ } break; case NSStreamEventNone: break; //打開完成 case NSStreamEventOpenCompleted: { NSLog(@"NSStreamEventOpenCompleted"); } break; default: break; } } @end

NSOutputStream

NSOutputStream 對應的是寫文件，它是要將已存在的內存(buffer)裏的數據寫入文件, 下面同樣一段是測試代碼

- (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裏的數據，寫入文件 self.location += bufSize; if (self.location >= [[self dataWillWrite] length] ) { //寫完後關閉流 [aStream close]; } } break; case NSStreamEventEndEncountered: { [aStream close]; } break; //錯誤和無事件處理 case NSStreamEventErrorOccurred:{ } break; case NSStreamEventNone: break; //打開完成 case NSStreamEventOpenCompleted: { NSLog(@"NSStreamEventOpenCompleted"); } break; default: break; } }

用途

NSInputStream 和 NSOutputStream 常用與網絡傳輸中，比如要將一個很大的文件傳送給服務器，那麼NSInputStream這時候是 很好的選擇, 我們可以查看到 NSURLRequest 有一個屬性叫HTTPBodyStream， 這時只要設置好一個NSInputStream的實例就可以 了，最大的好處就是可以節省我們很多的內存。

另外要說明的是，NSInputStream 和 NSOutputStream其實是對 CoreFoundation 層對應的CFReadStreamRef 和 CFWriteStreamRef 的高層抽象。在使用CFNetwork時，常常會使用到CFReadStreamRef 與 CFWriteStreamRef。 下面是一段相關代碼

// 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; }