macOS NSConcreteAttributedString mutableString crash

[mdeh]

Hi all,
I have a problem that I cannot understand!

According to the documentation, there is a method "mutableString" which, in the NSMutableAttributedString class

Returns the character contents of the receiver as an NSMutableString object.

So, with this code

NSMutableString * s = [_mString mutableString];

I would have expected s to be a mutableString. Here is the error:

-[NSConcreteAttributedString mutableString]: unrecognized selector sent to instance 0x100474560

Changing to this code:

NSString * s = [_mString string];

eliminates this issue...but the question is why? The literature that I have looked at does not seem to have an answer.

Thanks as usual.

 

[kainjow]

NSMutableAttributedString's methods aren't inherited by NSAttributedString. So any method specifically defined for NSMutableAttributedString will not work on NSAttributedString.

If you want a mutable string for NSAttributedString just call mutableCopy on the string.

How is _mString created?

 

[mdeh]

NSMutableAttributedString's methods aren't inherited by NSAttributedString. So any method specifically defined for NSMutableAttributedString will not work on NSAttributedString.
How is _mString created?

Kainjow...thanks, first off.

-mString is created by by taking the textStorage property of an NSTextView, and setting an NSMutableAttributed string using an accessor thus.

-(void) setMString:(NSMutableAttributedString *) m
{
	if ( m == nil)
	{
		return;
	}
	m = [m copy];
	[_mString release];
	_mString = m;

Earlier, I removed the actual use of the setter to make it read more easily, but here is the actual call to set it.

[[self cypherCenter] setMString:[[self cypherField]textStorage]];

Where cypherCenter is the class that has the accessor setMString.


Where I am a little confused is that the method:
- (NSMutableString *)mutableString is described within the NSMutableAttributedString Class and shows that an NSMutableString is returned, which is what I thought I was doing , but apparently not! Well, it was causing this issue. Still a little confused, but thanks for your input.

 

[kainjow]

m = [m copy];

Try using mutableCopy here.

Have a read through the section Copying Mutable Versus Immutable Objects (at the bottom). Basically, if you call copy on a mutable object, it will return an immutable one instead. This applies to things like NSArray, NSString, NSDictionary, etc., and other classes that have a separate mutable version.

 

[mdeh]

m = [m copy];

Try using mutableCopy here.

Have a read through the section Copying Mutable Versus Immutable Objects (at the bottom).

Now I have!!

That's clearly what's going on.
Thanks again.