Question

I am trying to subclass NSInputStream and NSOutputStream to keep track of the command I am passing to my server. This way, when I receive a response back from the server, I know which command it was a response to. When I try to set the command string in my subclass, I get an unrecognized selector error.

Subclasses:

PCFInputStream.h

#import <Foundation/Foundation.h>

@interface PCFInputStream : NSInputStream
@property (nonatomic, strong) NSString *command;
@end

PCFOutputStream.h

#import <Foundation/Foundation.h>

@interface PCFOutputStream : NSOutputStream
@property (nonatomic, strong) NSString *command;
@end

The .m files just have the command property synthesized so I can call setCommand:

Here is the class I am using these in:

 //instance vars in my class
 PCFInputStream *inputStream;
 PCFOutputStream *outputStream;


-(void)followClass:(id)sender
{
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;
    CFStreamCreatePairWithSocketToHost(NULL, (CFStringRef) SERVER_ADDRESS, PORT,     &readStream, &writeStream);
    inputStream = (__bridge_transfer PCFInputStream *)readStream;
    outputStream = (__bridge_transfer PCFOutputStream *)writeStream;
    [inputStream setDelegate:self];
    [outputStream setDelegate:self];
    [inputStream scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    [outputStream scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    [inputStream setCommand:[NSString stringWithFormat:@"%d,%@",[sender tag], [class classTitle]]];
    [inputStream open];
    NSString *str = [NSString stringWithFormat:@"_ADD_CLASS*%@*%@*%@*%@;", [class CRN], deviceToken, [class classLink],[class courseNumber]];
    [outputStream setCommand:str];
    [outputStream open];
}

Here is the error I get when it runs the line

[inputStream setCommand:[NSString stringWithFormat:@"%d,%@",[sender tag], [class classTitle]]];

-[__NSCFInputStream setCommand:]: unrecognized selector sent to instance 0x1e691170
2012-12-01 21:56:20.777 PCF[15610:907] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFInputStream setCommand:]: unrecognized selector sent to instance 0x1e691170'
*** First throw call stack:
(0x3a1b73e7 0x39043963 0x3a1baf31 0x3a1b964d 0x3a111208 0xfa267 0x39585047 0x39584ffb 0x39584fd5 0x3958488b 0x39584d79 0x394a3441 0x3a18c941 0x3a18ac39 0x3a18af93 0x3a0fe23d 0x3a0fe0c9 0x3743733b 0x394ee291 0x100005 0xe7d48)
libc++abi.dylib: terminate called throwing an exception

Can someone suggest a simple solution for me? I tried wrapping a NSStreamInput instance and my NSString* command into another class, but that doesn’t work for my purposes.

Thanks!

Answer 1

You can’t just cast an NSInputStream to a PCFInputStream. The object has to be created as a PCFInputStream, and CFStreamCReatePairWithSocketToHost doesn’t do that.

You can just attach a command property to NSInputStream in a category by using an associated object. Here’s the category interface:

@interface NSInputStream (PCFCommand)
@property (nonatomic) NSString *pcf_command;
@end

You implement it like this:

#import <objc/runtime.h>

@implementation NSInputStream (PCFCommand)

static int kPCFCommandKey;

- (NSString *)pcf_command {
    return objc_getAssociatedObject(self, &kPCFCommandKey);
}

- (void)setPcf_command:(NSString *)pcf_command {
    objc_setAssociatedObject(self, &kPCFCommandKey, [pcf_command copy],
        OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end