objective-c – 如何创建NSInputStream的子类？

2019年8月3日 182次阅读

我想创建一个NSInputStream的子类.简单地说,我尝试编码如下,

@interface SeekableInputStream : NSInputStream
{
    NSUInteger startOffset;
    NSUInteger totalReadLen;
}

- (NSInteger)read:(uint8_t *)buffer maxLength:(NSUInteger)len;
- (BOOL)getBuffer:(uint8_t **)buffer length:(NSUInteger *)len;
- (BOOL)hasBytesAvailable;
- (void)open:(NSUInteger)offset;

@end

而且,我使用了类似下面的类.

SeekableInputStream *stm = [[SeekableInputStream alloc] initWithURL:url];

然后,在运行时,我可以遇到以下错误消息.

– [SeekableInputStream initWithURL：]：无法识别的选择器发送到实例0x10018ff30

我没有故意覆盖initWithURL以使用父方法.
根据我的知识,派生类可以使用父类的方法,不是吗？

不能继承像initWithURL这样的扩展方法吗？

有没有人告诉我如何进行NSInputStream的子类化？

最佳答案 来自NSStream.h

// NSStream is an abstract class encapsulating the common API to NSInputStream and NSOutputStream.
// Subclassers of NSInputStream and NSOutputStream must also implement these methods.
@interface NSStream : NSObject
- (void)open;
- (void)close;

- (id <NSStreamDelegate>)delegate;
- (void)setDelegate:(id <NSStreamDelegate>)delegate;
 // By default, a stream is its own delegate, and subclassers of NSInputStream and NSOutputStream must maintain this contract. [someStream setDelegate:nil] must restore this behavior. As usual, delegates are not retained.

- (id)propertyForKey:(NSString *)key;
- (BOOL)setProperty:(id)property forKey:(NSString *)key;

- (void)scheduleInRunLoop:(NSRunLoop *)aRunLoop forMode:(NSString *)mode;
- (void)removeFromRunLoop:(NSRunLoop *)aRunLoop forMode:(NSString *)mode;

- (NSStreamStatus)streamStatus;
- (NSError *)streamError;
@end

// NSInputStream is an abstract class representing the base functionality of a read stream.
// Subclassers are required to implement these methods.
@interface NSInputStream : NSStream
- (NSInteger)read:(uint8_t *)buffer maxLength:(NSUInteger)len;
// reads up to length bytes into the supplied buffer, which must be at least of size len. Returns the actual number of bytes read.

- (BOOL)getBuffer:(uint8_t **)buffer length:(NSUInteger *)len;
// returns in O(1) a pointer to the buffer in 'buffer' and by reference in 'len' how many bytes are available. This buffer is only valid until the next stream operation. Subclassers may return NO for this if it is not appropriate for the stream type. This may return NO if the buffer is not available.

- (BOOL)hasBytesAvailable;
// returns YES if the stream has bytes available or if it impossible to tell without actually doing the read.
@end

如您所见,没有initWithURL函数.所以,你的超级不起作用,因为它确实不存在.就像MrTJ所说,这是一个类别.它定义于：

// The NSInputStreamExtensions category contains additional initializers and convenience routines for dealing with NSInputStreams.
@interface NSInputStream (NSInputStreamExtensions)
- (id)initWithURL:(NSURL *)url NS_AVAILABLE(10_6, 4_0);

所以,我认为如果你在你的子类中使用它,它可以工作.

#import <Foundation/NSStream.h>

您需要导入类别.记住你不能继承一个类别,只是覆盖它然后不能调用(或者如果能,我不知道怎么做)

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