Objective-C NSMutableArray: Problem with sorting objects?

Question

I currently have an object called Station defined as:

@interface RFStation : NSObject {

    NSString *stationID; 
    NSString *callsign; 
    NSString *logo; 
    NSString *frequency;
@end

I also have an NSMutableArray containing a list of 'Station' objects. I need to have a method to sort these objects by the 'stationState' attribute.

I implemented this method:

NSComparisonResult compareCallSign(RFStation *firstStation, RFStation *secondStation, void *context) {
    if ([firstStation.stationState compare:secondStation.stationState]){
        return NSOrderedAscending;
    }else{
        return NSOrderedDescending;
    }

}

and call it using:

[stationList sortedArrayUsingFunction:compareState context:nil];
[self.tableView reloadData]

(the data is loaded into a UITableViewController)

Can someone please tell me why my NSMutableArray is not getting sorted?

kennytm · Accepted Answer · 2010-08-16 07:08:25Z

2

-sortedArrayUsingFunction:… does not modify the array. It just copies the array, sort it, and return the new sorted one.

To sort the mutable array in-place, use the -sortUsingFunction:context: method.

[stationList sortUsingFunction:compareState context:nil];
[self.tableView reloadData];

BTW,

The -compare: method already returns a NSComparisonResult. Your function should be implemented as

NSComparisonResult compareCallSign(...) {
    return [firstStation.stationState compare:secondStation.stationState];
}

you could just use an NSSortDescriptor.

NSSortDescriptor* sd = [NSSortDescriptor sortDescriptorWithKey:@"stationState" 
                                                     ascending:YES];
[stationList sortUsingDescriptors:[NSArray arrayWithObject:sd]];
[self.tableView reloadData];

answered Aug 16, 2010 at 7:08

kennytm

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1 Comment

dpigera Over a year ago

WOW!! Your second solution was fantastic.. Thank-you soo much. Now only if there was a way to give a +3 for a solution.

Gary · Accepted Answer · 2010-08-16 07:08:02Z

0

well something obvious, you've named your sort method compareCallSign and you've passed compareState to sortedArrayUsingFunction

answered Aug 16, 2010 at 7:08

Gary

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