Question

So I need to add the objects from an NSArray that the user has chosen using an NSOpenPanel and put all the filenames into this array. Then I have an NSMutableArray called arguments that I am putting the arguments programmatically. Then I need to add these objects from the NSArray to the end of this NSMutableArray. So I use [NSMutableArray addObjectsFromArray:NSArray] and that keeps giving me an error.

This is what I’m doing with the code:
AppDelegate.h

#import <Cocoa/Cocoa.h>

@interface ZipLockAppDelegate : NSObject <NSApplicationDelegate> {
    IBOutlet NSTextField *input;
    IBOutlet NSTextField *output;
    IBOutlet NSTextField *password;
    NSArray *filenames;
    NSMutableArray *arguments;
    NSArray *argumentsFinal;
}

@property (assign) IBOutlet NSWindow *window;
@property (retain) NSArray *filenames;
@property (copy) NSMutableArray *arguments;

- (IBAction)chooseInput:(id)sender;
- (IBAction)chooseOutput:(id)sender;
- (IBAction)createZip:(id)sender;

@end

AppDelegate.m

#import "ZipLockAppDelegate.h"

@implementation ZipLockAppDelegate

@synthesize window = _window;
@synthesize filenames;
@synthesize arguments;

- (IBAction)chooseInput:(id)sender {
    NSOpenPanel *openZip = [[NSOpenPanel alloc] init];
    [openZip setCanChooseFiles:YES];
    [openZip setCanChooseDirectories:YES];
    [openZip setCanCreateDirectories:NO];
    [openZip setAllowsMultipleSelection:YES];
    [openZip setTitle:@"Select All Files/Folders to be zipped"];
    int result = [openZip runModal];
    if (result == 1) {
        filenames = [openZip filenames];
    }
}

- (IBAction)createZip:(id)sender {
    [progress startAnimation:self];
    arguments = [NSMutableArray arrayWithObjects:@"-P", [password stringValue], [output stringValue], nil];
    [self.arguments addObjectsFromArray:filenames];
    argumentsFinal = [[NSArray alloc] initWithArray:self.arguments];
    NSTask *makeZip = [[NSTask alloc] init];
    [makeZip setLaunchPath:@"/usr/bin/zip"];
    [makeZip setArguments:argumentsFinal];
    [makeZip launch];
    [makeZip waitUntilExit];
    [progress stopAnimation:self];
}

And this is the error I keep getting in the log. I can’t figure out why I’m getting this.

EXC_BAD_ACCESS(code=13,address=0x0)

This points to the line [arguments addObjectsFromArray:filenames];

I can only make out the first part about the selector and the instance but I don’t know what it means. Help…

Answer 1

Be consistent. To begin with, prefix all your instance variables with an underscore, not just some of them.

 // Change this...
@synthesize window = _window;
@synthesize filenames;
@synthesize arguments;

//...to this
@synthesize window = _window;
@synthesize filenames = _filenames;
@synthesize arguments = _arguments;

Then you won’t be able to do this anymore:

arguments = [NSMutableArray arrayWithObjects:@"-P", [password stringValue], [output stringValue], nil];

Note that on the very next line, you’re doing this:

[self.arguments addObjectsFromArray:filenames];

Again, being consistent in using properties rather than directly accessing instance variables will help you avoid these kinds of errors. So rewrite the previous line to use the property, like so:

self.arguments = [NSMutableArray arrayWithObjects:@"-P", [password stringValue], [output stringValue], nil];

The compiler translates self.arguments = someArg into [self setArguments:someArg]. In this case the setter method is needed to retain the object so that it won’t be deallocated while the reference is still stored in the _arguments instance variable.