NSTextField Subclass Crashes on setLineBreakMode: method

Question

I have a subclass of NSTextField and I setting the LineBreakMode.

It works fine under my mac with Yosemite and Crashes for one of my users on Mavericks

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[XTextField setLineBreakMode:]: unrecognized selector sent to instance 0x7fc784548ad0'

How could I work this round ?

Header File of the subclass

#import <Cocoa/Cocoa.h>

@interface XTextField : NSTextField

- (void)setText:(NSString *)text

@end

Implementation

#import "XTextField.h"
@implementation XTextField

- (void)setText:(NSString *)text
{
    if (text)
    {
        [self setStringValue:text];
    }
    else
    {
        [self setStringValue:@""];
    }
 }


 - (instancetype)initWithFrame:(NSrect)frame
 {
     if(self = [super initWithFrame:frame])
     {
         [self setEditable:NO];
         [self setSelectable:NO];
         [self setDrawsBackGround:NO];
         [self setBezeled:NO];
     }
     return self;
 }
 @end

Calling code:

XTextField* myLabel = [[XTextField alloc]initWithFrame:myFrame];
[myLabel settext:@"text text text"];
[myLabel setLineBreakMode:NSLineBreakByTruncatingTail];

Answer 1

There are lots of questions that need to be answered here. The problem, as indicated by the error message, is that the setLineBreakMode: selector was sent to an object that doesn't recognize that selector. What could be happening that would cause that? Figuring things like this out requires critical thinking and detective work. Here are some ideas.

1. -setLineBreakMode: does not seem to actually be implemented by NSTextField; it is a method of NSCell, and of NSMutableParagraphStyle, as far as I can tell. If you have an NSTextField (or a subclass of it) you'd normally call [[myTextField cell] setLineBreakMode:...], but your code snippet doesn't indicate that you are doing that. So unless you implemented this method in your subclass – which you don't state that you did – this is probably the reason for the crash. Perhaps you don't see the crash on your Mac because this code path doesn't get hit, for whatever reason? Or perhaps Apple privately implemented this method in Yosemite but not in Mavericks? Who knows. Do you get a warning from the compiler on that line, saying that the object does not respond to that selector? Do not ignore compiler warnings.

2. The code you posted looks like you are calling setLineBreakMode: on the class object, not on an instance of the class; normally classes start with a capital letter, whereas instances start with a lowercase letter. Obeying coding conventions like this makes things much less confusing for everybody. And if your subclass is really named NSTextFieldSubClass, then I agree with @MichaelDautermann that you should never, ever name classes with an NS prefix; that is both confusing and asking for trouble, since for all you know Apple has a private subclass with exactly that name. Class names beginning with NS are reserved by Apple.

3. It could be that the object you think is in the variable that you have apparently named NSTextFieldSubClass is not an instance of your subclass at all, or has been freed (and perhaps replaced by a new object at the same address), or some such problem, and that that is why it doesn't respond to the selector. You could investigate this by turning on NSZombieEnabled, examining it in the debugger, adding an NSLog of it (perhaps with an added -description method in your subclass), or many other techniques.

That's all pretty vague, but then the question is vague. You need to post the code for your subclass, the code where you instantiate the subclass, and the code surrounding the line that crashes, at a minimum, to get more specific help. We can't read your mind, and the root of the bug may well be in one of those places.