Pass arguments between Objective-C applications

Question

I was wondering if it is possible to pass arguments between Mac applications and if it possible, how.

I know that in Java is possible using the following syntax from the command line:

java JavaApp arg1 arg2 arg3 arg4

And that is possible to access those through the main's args[] array.

public static void main(String[] args) {
        System.out.println("d");
        for (int i = 0; i < args.length; i++)
            System.out.println(args[i]);
}

Edit: I want to pass the arguments from a command line Mac application to a Cocoa Mac application

Answer 1

It's not clear to me why your Restarter app needs to be a Cocoa application. However, on the assumption that it does, command line arguments are available in the argument domain of the NSUserDefaults. This link shows how to invoke the program from the command line and how to specify the default name.

The Cocoa way to kick off a separate process is to use NSTask.

Answer 2

If both the command line and GUI applications are written in Objective-C you could potentially use NSDistributedNotificationCenter to send notifications between the processes. Documentation for NSDistributedNotificationCenter can be found in the Notification Programming Guide.

Alternatively, Cocoa GUI applications accept command line parameters in the same way as any other C program, i.e. the argv and argc parameters of the main subroutine.

Answer 3

The following is a category I wrote on NSWorkspace that allows for an argv type array of arguments to be passed to the resulting app.

@interface NSWorkspace (MDAdditions)
- (BOOL)launchApplicationAtPath:(NSString *)path
                      arguments:(NSArray *)argv
                          error:(NSError **)outError;
@end

@implementation NSWorkspace (MDAdditions)

- (BOOL)launchApplicationAtPath:(NSString *)path
                      arguments:(NSArray *)argv
                          error:(NSError **)outError {
    NSParameterAssert(path != nil);
    BOOL success = YES;
    if (outError) *outError = nil;
    FSRef itemRef;
    OSStatus status = FSPathMakeRef((const UInt8 *)[path UTF8String], &itemRef, NULL);
    if (status != noErr) {
        if (anError) *anError = [NSError errorWithDomain:NSOSStatusErrorDomain
                        code:status userInfo:nil];
        return NO;
    }
    LSApplicationParameters appParameters = {0, kLSLaunchDefaults, &itemRef,
         NULL, NULL, (argv ? (CFArrayRef)argv : NULL), NULL };
    status = LSOpenApplication(&appParameters, NULL);
    if (status != noErr) {
         NSLog(@"LSOpenApplication() returned %d for %@", (int)status, path);
         if (outError) *outError = [NSError errorWithDomain:NSOSStatusErrorDomain
                        code:status userInfo:nil];
         return NO;
    }
    return YES;
}
@end

UPDATED:

As mentioned in the answers to Accessing command-line arguments in Objective-C, the "_" prefix of the _NSGetArgv() and _NSGetArgc() functions is usually a sign that they are private and should be avoided if an alternative is available (which there is).

To get the args passed to the executable, you can use NSProcessInfo's -arguments method as in the following code:

NSArray *argv = [[NSProcessInfo processInfo] arguments];
NSArray *args = [argv subarrayWithRange:NSMakeRange(1, argv.count - 1)];
NSLog(@"args == %@", args);

Answer 4

All your answers worked properly for me, but I found another solution that suits better my needs. I needed to launch a Cocoa app from a Command Line Tool, which I achieved with the following line:

system("nohup /PATH/Arguments.app/Contents/MacOS/Arguments argument1 argument2 &");

nohup is unix service that allows you to attach processes to itself so if you close the terminal window, the process remains alive.

Next problem that came along was capturing the arguments from within the Cocoa app. "How would I get the arguments from AppDelegate.m if main.m is the one that receives them and just returns an int."

Among Apple's frameworks and libraries I found one that exactly solved the problem. This library is called crt_externs.h and contains two useful variables, one to learn the number of arguments, and another one to obtain the arguments themselves.

extern char ***_NSGetArgv(void);
extern int *_NSGetArgc(void);

So, inside at the AppDelegate's from the Cocoa app we would write the following code to parse the arguments into NSString's:

char **argv = *_NSGetArgv();
NSString *argument1 = [NSString stringWithCString:argv[1] encoding:NSUTF8StringEncoding];
NSString *argument2 = [NSString stringWithCString:argv[2] encoding:NSUTF8StringEncoding];

As we can see we skip directly to the position 1 of the arguments array since position 0 contains the path itself:

argv[0] = '/PATH/Arguments.app/Contents/MacOS/Arguments'
argv[1] = 'argument1'
argv[2] = 'argument2'

Thank you all for your time and help. I learned a lot from you guys. I also hope this answer helps someone else :)

Cheers and happy coding!