Does Nssortdescriptor convert contents of the array to integer after sorting?

问题

Given the below code, in the first iteration the logs are displayed normally. For the second iteration the app crashes with the following error message:

019-11-07 09:54:08.156277+0100 xxxion[520:202084] iconNumberString : 1026
2019-11-07 09:54:12.160849+0100 xxxtion[520:202084] [self.iconNumbers lastObject]) : 1026
2019-11-07 09:54:24.598805+0100 xxxion[520:202084] -[__NSSingleObjectArrayI addObject:]: unrecognized selector sent to instance 0x2824a3fd0
(lldb)

The nssortdescriptor used:

        NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"intValue" ascending:YES];

To solve this issue: 1-as I thought that the nssordescriptor converts the contents of the array to integer as the specified key specifies in the nssortdescriptor, the following log added: NSLog(@"[self.iconNumbers lastObject]) : %i", [self.iconNumbers lastObject]); to check if the values were converted to integer or not

the question is: 1-does nssortdescriptopn converts the contents of the NSArray to integer as the nssordescriptor specifies -initWithKey:@"intValue"-?

2-for this line_

 self.iconNumbers = (NSMutableArray *)[self.iconNumbers    
 sortedArrayUsingDescriptors:@[sortDescriptor]];

why the changes should not have been applied directly on -self.iconnumbers-?? why I have to assign the results of the RightHandSide to the same -self.iconnumber- again??

code:

For loop 
 [self.iconNumbers addObject:iconNumberString];
         self.iconNumbers = (NSMutableArray *)[self.iconNumbers sortedArrayUsingDescriptors:@[sortDescriptor]];
        NSLog(@"iconNumberString : %@", iconNumberString);
        NSLog(@"[self.iconNumbers lastObject]) : %@", [self.iconNumbers lastObject]);

        NSLog(@"[self.iconNumbers lastObject]) : %i", [self.iconNumbers lastObject]);//added for testing after received the crash
End of loop

回答1:

sortedArrayUsingDescriptors: returns a NSArray. It's not applying on itself, it's applying on a "copy" and returning the sorted copy.

Casting, ie doing (NSMutableArray *)something isn't magic. It won't transform the NSArray into a NSMutableArray. It just tells the compiler, don't be afraid, I'm telling you it's a NSMutableArray, treat it as such for the next time, trust me (and you're wrong).

Either, use sortUsingDescriptors: directly, or replace (NSMutableArray *) with [[NSMutableArray alloc] initWithArray:

For loop 
    [self.iconNumbers addObject:iconNumberString];
    self.iconNumbers = [[NSMutableArray alloc] initWithArray:[self.iconNumbers sortedArrayUsingDescriptors:@[sortDescriptor]]];
End of loop

For loop 
    [self.iconNumbers addObject:iconNumberString];
    [self.iconNumbers sortUsingDescriptors:@[sortDescriptor]];
End of loop

For the rest:

It will use the sortDescriptor as a "conversion" for the sort, but it won't replace the value with the conversion. Imagine, you have an array of NSDictionary looking like this: @{@"key1": @"Hello", @"key2": @"Hi"}, setting the descriptor won't replace each dictionary with the value of key1 (Hello).

Finally, you can only have a NSObject in a NS(Mutable)Array, no primitive. It'd be then, at the max, a NSNumber encapsulating a Int.

来源：https://stackoverflow.com/questions/58745408/does-nssortdescriptor-convert-contents-of-the-array-to-integer-after-sorting

标签

objective-c

nsmutablearray

nsarray

nssortdescriptor