Question

I have a global NSMutableArray and I need to update it with values. NSMutableArray is defined in the .h as follows;

@property (strong, nonatomic) NSMutableArray *myDetails;

In the viewDidLoad pre-populate like this;

    NSDictionary *row1 = [[NSDictionary alloc] initWithObjectsAndKeys:@"1", @"rowNumber", @"125", @"yards", nil];
    NSDictionary *row2 = [[NSDictionary alloc] initWithObjectsAndKeys:@"2", @"rowNumber", @"325", @"yards", nil];
    NSDictionary *row3 = [[NSDictionary alloc] initWithObjectsAndKeys:@"3", @"rowNumber", @"525", @"yards", nil];
self.myDetails = [[NSMutableArray alloc] initWithObjects:row1, row2, row3, nil];

Then when the user changes a text field this code is run this;

-(void)textFieldDidEndEditing:(UITextField *)textField{
    NSObject *rowData = [self.myDetails objectAtIndex:selectedRow];

    NSString *yards = textField.text;

    [rowData setValue:yards forKey:@"yards"];

    [self.myDetails replaceObjectAtIndex:selectedRow withObject:rowData];
}

When stepping through the code on the line [rowData setValue:yards forKey:@”yards”]; it returns this error;

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'

Answer 1

The array is mutable, but what is in it… NSDictionary… is not. You grab an object out of the array…

NSObject *rowData = [self.myDetails objectAtIndex:selectedRow];

and then you try to mutate that object…

[rowData setValue:yards forKey:@"yards"];

The object in the array is the thing you are changing… and it is NSDictionary, immutable, and you can not change it. If you want the dictionary to be mutable, you have to use NSMutableDictionary