Disable Option-Enter line breaks in NSTextField?

I want to disallow entering a new-line character in my NSTextField, which by default is possible by typing Option-Enter (or Option-Return).

While I found some pages explaining how to allow line breaks without having to use the Option modifier, I couldn't find anything for disabling line breaks altogether.

How can this be done?

You could create a subclass of NSFormatter and implement the isPartialStringValid:... method to block the newline.

- (BOOL)isPartialStringValid:(NSString **)partialStringPtr 
       proposedSelectedRange:(NSRangePointer)proposedSelRangePtr 
              originalString:(NSString *)origString 
       originalSelectedRange:(NSRange)origSelRange 
            errorDescription:(NSString **)error
{
    // the user may have:
    // -- deleted the left most character
    // -- deleted the last character and we have an empty string
    // both cases are valid
    if (proposedSelRangePtr->location == 0)
        return YES;

    unichar theChar = [*partialStringPtr characterAtIndex:proposedSelRangePtr->location - 1];

    if ([[NSCharacterSet newlineCharacterSet] characterIsMember:theChar]) {
        *error = nil;
        NSBeep();
        return NO;
    }

    return YES;
}