Question

I am trying to assign objects in an NSMutableArray using this code

- (IBAction)variablePressed:(UIButton *)sender {
NSString *variable = [sender currentTitle];
if (!_variableToBePassedIntoTheDictionary) _variableToBePassedIntoTheDictionary = [[NSMutableArray alloc] init];
[_variableToBePassedIntoTheDictionary replaceObjectAtIndex:0 withObject:variable];}

but when I run this program the program breaks at the last line, since I have set the debugger to show warnings if a Exception is raised. Running the program without breakpoints, the program gives SIGARBT and crashes. I then assign these values to a dictionary which would be passed to the Model for further calculations.

- (IBAction)testVariableValues:(id)sender {
if (!_variablesAssignedInADictionary) _variablesAssignedInADictionary = [[NSMutableDictionary alloc] init];
[_variablesAssignedInADictionary setObject:_digitToBePassedIntoTheVariable forKey:_variableToBePassedIntoTheDictionary];
NSLog(@"%@", _variablesAssignedInADictionary);}

P.S. I am new in Objective C, can anybody please explain when do we use

@synthesize someProperty;

vs

@synthesize someProperty = _someProperty;

Thank You!

Answer 1

The first time the method is called you create the NSMutableArray and then attempt to replace an object which is not there. The reference says:

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject

The index of the object to be replaced. This value must not exceed
the bounds of the array. Important Raises an NSRangeException if
index is beyond the end of the array.

And 0 will exceed the bounds of an empty array.

Try this instead:

- (IBAction)variablePressed:(UIButton *)sender
{
    NSString *variable = [sender currentTitle];
    if (_variableToBePassedIntoTheDictionary == nil)
    {
        _variableToBePassedIntoTheDictionary = [[NSMutableArray alloc] init];
        [_variableToBePassedIntoTheDictionary addObject:variable];
    }
    else
    {
        [_variableToBePassedIntoTheDictionary replaceObjectAtIndex:0 withObject:variable];
    }
}