CODEWITHSUNDEEP
objective-cnsnumber
Le Mot Juiced
Le Mot Juiced

Reputation: 3849

Why is NSDecimalNumber crashing when I try to use decimalNumberByMultiplyingBy:?

I'm trying to retrieve a number from user defaults and multiply it. Here's my code: 

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
NSDecimalNumber *current = [prefs  objectForKey:@"account"];
NSDecimalNumber *multiplier = [NSDecimalNumber decimalNumberWithString:@"1.15"];
NSDecimalNumber *floo = [current decimalNumberByMultiplyingBy: multiplier];

It's giving me this really hideous crash as soon as it hits the floo line. The huge spew of error gobbledygook begins with:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', 
reason: '-[__NSCFNumber decimalNumberByMultiplyingBy:]: unrecognized selector 
sent to instance 0x8c7b1e0'

This seemed like a very simple thing, but my goodness! What's happening?

Upvotes: 0

Views: 1018

Answers (2)

RickJansen
RickJansen

Reputation: 1713

Better may be to use an archiver, like storing the object as:

[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:current] forKey:@"account"];

and retrieving it:

current = [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:@"account"] ];

That is more reliable I think than seeing that you actually have an __NSCFNumber back, and converting that.

Upvotes: 0

Seamus Campbell
Seamus Campbell

Reputation: 17916

You've assigned the value of [prefs objectForKey:@"account"] to an NSDecimalNumber variable, but the actual value is an NSNumber, not an NSDecimalNumber. When you try to call -decimalNumberByMultiplyingBy: on that object, your program crashes, because that object doesn't know what to do with that method.

You can convert an NSNumber to an NSDecimalNumber like this:

NSNumber *number = /* ... */
NSDecimalNumber *decimalNumber = 
    [NSDecimalNumber decimalNumberWithDecimal:[number decimalValue]];

Upvotes: 5

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