Can't create global function in Objective - C

Question

I'm trying to create global function in Objective-C. I created new .m and h. file with subclass of viewcontroller.

This is Connection.m

#import "Connection.h"
@interface ViewController () <NSStreamDelegate>

@property (strong,nonatomic) NSInputStream * inputStream;
@property (strong,nonatomic) NSOutputStream * outputStream;

@end

@implementation ViewController(Connection)
-(void)initNetworkCommunication {
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;
    CFStreamCreatePairWithSocketToHost(NULL, (CFStringRef)@"192.168.0.10", 35000, &readStream, &writeStream);
    self.inputStream = objc_unretainedObject(readStream);
    self.outputStream = objc_unretainedObject(writeStream);
    [self.inputStream setDelegate:self];
    [self.outputStream setDelegate:self];
    [self.inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [self.outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

    [self.inputStream open];
    [self.outputStream open];
}

Connection.h

#import "ViewController.h"

@interface ViewController(Connection)

-(void)initNetworkCommunication;

@end

ViewController.m

#import "ViewController.h"
#import "Connection.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)ConnectionButton:(id)sender {
    [self initNetworkCommunication];
}

@end

I tryed 3 methods mentioned in How to create global functions in Objective-C but no one of this 3 works. First two(create a class method in a static class and declare a global function instead of class) don't work because when I change "-(void)... to +(void).. every "self..." gets error and same in second method. Only third one works for me (adding a category to NSObject for your methods) but when I'm trying to call [self initNetworkCommunication] function program crashesh with signal SIGABRT and I can't solve that problem. Any ideas how I can call this function?

UPDATE: @gronzzz

Connection.m

@interface ViewController () <NSStreamDelegate>

@property (strong,nonatomic) NSInputStream * inputStream;
@property (strong,nonatomic) NSOutputStream * outputStream;

@end

@implementation Connection

-(void)initNetworkCommunication 
Connection.h

#import "ViewController.h"

@interface Connection : ViewController

-(void)initNetworkCommunication;
@end
ViewController.h

#import "ViewController.h"
#import "Connection.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (void)callMethod
{
    Connection *detailVC = [[Connection alloc] init];
    [detailVC initNetworkCommunication];
}
- (IBAction)ConnectionButton:(id)sender {
    [self callMethod];

}

@end

And Signal SIGABRT show when [self callMethod] is called.

Answer 1

To call one instance method from another class, you just need to initialize this class and them call. Calling method must be inside @interface brackets. Also don't understand why did you call "[self initNetworkCommunication]", for that you needn't category or something else.

DetailViewController.h

@interface DetailViewController : UIViewController

-(void)initNetworkCommunication;
@end

DetailViewController.m

@implementation DetailViewController
-(void)initNetworkCommunication
{
     // do something
}
@end

MasterViewController.h

@implementation MasterViewController
- (void)callMethod
{
    DetailViewController *detailVC = [[DetailViewController alloc] init];
    [detailVC initNetworkCommunication];
}
@end

UPDATE

in .h file you are making interface category, in .m file you are making class extension and then implementation of class, but you still doesn't makes interface for your class.

Answer 2

I am trying to figure out what exactly you are trying to accomplish based on your code. It seems as though you want one of two things. You either want a global function which will initialize an input and output stream given to it by an object, or you want something called a singleton which will itself hold the input and output stream and can be initialized by anywhere.

Based on your example, I will assume that you want the function, if it is in fact the singleton pattern that sounds more correct, feel free to search for objective-c singleton pattern.

+(void)initNetworkCommunicationWithInputStream:(NSInputStream *)inputStream outputStream:(NSOutputStream *)outputStream delegate:(id < NSStreamDelegate >)delegate {
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;
    CFStreamCreatePairWithSocketToHost(NULL, (CFStringRef)@"192.168.0.10", 35000, &readStream, &writeStream);
    inputStream = objc_unretainedObject(readStream);
    outputStream = objc_unretainedObject(writeStream);
    [inputStream setDelegate:delegate];
    [outputStream setDelegate:delegate];
    [inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    [outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

    [inputStream open];
    [outputStream open];
}

You can have this method exist in some class and then you can call it without initializing that class and passing in the params you want setup:

[someClass initNetworkCommunicationWithInputStream:iStream outputStream:oStream delegate:self];

Answer 3

Assuming that you want a method named callMethod inside ViewController to be your "global" method:

+ (void)callMethod
{
    Connection *detailVC = [[Connection alloc] init];
    [detailVC initNetworkCommunication];
}

Invoked with:

[ViewController callMethod];

But do note that your callMethod implementation does not return anything, and the Connection object created within it will be deleted on exit from the method (unless the call to initNetworkCommunication somehow preserves it).