Objective C - Adding a new row to empty NSTableView

Question

I have a View-Based NSTableView which should be initially empty. I also have "add" and "remove" buttons for adding and deleting rows from same NSTableView.

My delegate methods and method for adding new row look like this:

#import "PreferencesApiKeysViewController.h"
#import "UserKeys.h"

@interface PreferencesApiKeysViewController ()

@property (weak) IBOutlet NSTableView *keysTableView;

@end

@implementation PreferencesApiKeysViewController
- (NSView *)tableView:(NSTableView *)tableView viewForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row {
    // Get a new ViewCell
    NSTableCellView *cellView = [tableView makeViewWithIdentifier:tableColumn.identifier owner:self];

    if([tableColumn.identifier isEqualToString:@"userKeysColumn"]) {
        UserKeys *allKeys = [self.allKeys objectAtIndex:row];
        cellView.textField.stringValue = allKeys.userKeyName;
        return cellView;
    }
    return cellView;
}

- (NSInteger)numberOfRowsInTableView:(NSTableView *)tableView {
    NSLog(@"Initial rows: %li", (unsigned long)[self.allKeys count]);
    return [self.allKeys count];
}

- (IBAction)addKey:(id)sender {
    UserKeys *newKey = [[UserKeys alloc] initWithKeyName:@""
                                                   apiID:@""
                                                 apiCode:@"" ];

    [self.allKeys addObject:newKey];
    NSLog(@"Total rows: %li", (unsigned long)self.allKeys.count);
    NSInteger newRowIndex = self.allKeys.count;
    if (newRowIndex == 0) {
        NSLog(@"No rows.");
        newRowIndex = 0;
    } else {
        NSLog(@"Has rows.");
        newRowIndex = self.allKeys.count-1;
    }
    NSLog(@"New Index: %ld", (long)newRowIndex);

    [self.keysTableView insertRowsAtIndexes:[NSIndexSet indexSetWithIndex:newRowIndex] withAnimation:NSTableViewAnimationSlideDown];

    [self.keysTableView selectRowIndexes:[NSIndexSet indexSetWithIndex:newRowIndex] byExtendingSelection:NO];
    [self.keysTableView scrollRowToVisible:newRowIndex];
}

@end

and in my AppDelegate.m, I'm calling my view like this:

#import "AppDelegate.h"
#import "UserKeys.h"
#include "PreferencesApiKeysViewController.h"

@interface  AppDelegate()
@property (nonatomic,strong) IBOutlet PreferencesApiKeysViewController *prefsViewController;
@end

@implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    self.prefsViewController = [[PreferencesApiKeysViewController alloc] initWithNibName:@"PreferencesApiKeysViewController" bundle:nil];

    // Create few rows as dummy data
    /*
    UserKeys *key1 = [[UserKeys alloc] initWithKeyName:@"key one"
                                                 apiID:@"123"
                                               apiCode:@"xxx" ];

    UserKeys *key2 = [[UserKeys alloc] initWithKeyName:@"key two"
                                                 apiID:@"456"
                                               apiCode:@"yyy" ];
    NSMutableArray *tempKeys = [NSMutableArray arrayWithObjects:key1, key2, nil];
    self.prefsViewController.allKeys = tempKeys;
    */
    // done.

    [self.window.contentView addSubview:self.prefsViewController.view];
    self.prefsViewController.view.frame = ((NSView*)self.window.contentView).bounds;
}

@end

Now, the thing here is that if I uncomment those few lines for adding dummy data in AppDelegate and launch my app, everything works fine. I can add/remove rows without any problem, I can even delete all of them and add a new one after that.

But, if I comment those lines again, my app starts with an empty table (which is what I need), and when I want to add new row I get an error:

*** Assertion failure in -[NSTextFieldCell _objectValue:forString:errorDescription:], /SourceCache/AppKit/AppKit-1187.34/AppKit.subproj/NSCell.m

Looking further the thread, I see only one line referencing to my app:

0x0000000100003116 -[PreferencesApiKeysViewController tableView:viewForTableColumn:row:] + 406

I'm guessing that my TableView is not properly instantiated if allKeys array doesn't contain any single object really, but I'm not sure how to fix that? How to create an empty NSTableView and have the ability to add the first row by myself when "add" button is clicked (without adding any dummy data to allKeys)?

NSGod NSGod · Accepted Answer · 2013-02-21T14:39:29

Add this to the implementation of PreferencesApiKeysViewController:

@implementation PreferencesApiKeysViewController

- (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)bundle {
    if ((self = [super initWithNibName:nibName bundle:bundle])) {
        self.allKeys = [NSMutableArray array];
    }
    return self;
}

// add the following only if not using ARC
- (void)dealloc {
    [_allKeys release];
    [super dealloc];
}

@end

What's happening when you allow that commented-out code to be compiled in is that you assign an NSMutableArray instance to the allKeys instance variable. As a result, adding and removing items works as you would expect.

Generally, in a case like this, the class that manages the NSMutableArray should override the init method to make sure the array is properly initialized to an empty array. (By default, non-IBOutlet instance variables are initialized to nil, which won't allow you to properly add or remove items from it).

Objective C - Adding a new row to empty NSTableView

1 Answers