NSTextField value bound to NSObjectController won't accept text input or changes

Question

Here's what I've done so far:

1. I have created a class that contains an NSNumber.

2. I instantiated this class in my nib by dragging this object in the document window.

3. I brought an NSObjectController into the document window to manage this object. I changed the class and keys in the attributes window. I dragged a connection from this objects content button to the class I instantiated.

4. I put a text field in my window and bound it's Value to the NSNumber in my class (using an NSNumber formatter).

The result, when I compile, is that the text field displays "No Selection." When I click on the text field, this "No selection" disappears, but it won't let me edit the field. I would like to enter in numbers and have them change accordingly, but this is not happening now. What do I do? Any help is greatly appreciated, as always. Thanks in advance.

Here is the code for my class:

Parameters.h:

#import <Cocoa/Cocoa.h>

@interface Parameters : NSObject
{
 NSNumber *numberOfAtoms, *numberOfTrajectories;
}
@property(copy) NSNumber *numberOfAtoms, *numberOfTrajectories;
@end

Parameters.m:

#import "Parameters.h"

@implementation Parameters

@synthesize numberOfAtoms, numberOfTrajectories;

@end