iOS/objective-c: Spooky error setting value of object

Question

I have copied some code that works fine for saving an api to one entity in core data over to save a similar api to another entity. Although everything is largely the same, I cannot get rid of exception error.

Here is the code that throws the exception:

- (NSMutableArray *) convertFeedtoObject:(NSMutableArray*)feed {
    NSMutableArray * _newitems = [[NSMutableArray alloc] init];
    for (int i = 0; i < feed.count; i++) {
        NSDictionary *feedElement = feed[i];

        ItemOnServer *newItem = [[ItemOnServer alloc] init];
        newItem.itemtitle = feedElement[@"itemtitle"]; //throws exception
        newItem.item = feedElement[@"item"];//also throws an exception if above commented out
         newItem.descript = @"some item"; //if above lines commented out, littoral throws exception too.
//same goes for any other values I try to set.  The first one throws exception.

Here is the error:

2015-11-20 05:26:03.281 [20610:60b] -[ItemOnServer setItem:]: unrecognized selector sent to instance 0x175721b0

No matter what values I try to set, I get a similar error even though I know the values are there.

One item of the feed looks like this:

 {
        lastviewed = "2015-11-17 15:21:45";
        itemtitle = "New";
        id = 944;
        item = "cotton shirt";

    }
)

Thanks for any suggestions.

Edit:

Code from ItemOnServer.h

//.m file is largely empty
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
@class ItemsVC;
@class Vendors;

@interface ItemOnServer : NSObject
@property (nonatomic, retain) NSString * item;
@property (nonatomic, retain) NSNumber * id;//this is permanent id shared with server
@property (nonatomic, retain) NSNumber * localid; //this is temp id if first created locally
@property (nonatomic, retain) NSString * itemtitle;
@property (nonatomic, retain) NSDate * lastviewed;

//this is relationship with vendors
@property (nonatomic, retain) Vendors *vendor;

@end

Answer 1

It looks like your class ItemOnServer doesn't have implementations for the methods setItem:, setItemtitle and so on. I don't know how you managed to do this, but you should look at the interface and implementation of ItemOnServer.

Look at what the error message says:

 -[ItemOnServer setItem:]: unrecognized selector

That means a setItem: message is sent to an object, that object is an ItemOnServer object, and it doesn't implement setItem: The first two of these three points are exactly what you expect to happen when you write newItem.item = ...

Do you have another class named ItemOnServer in your application, maybe linked through some library? You can easily check by renaming ItemOnServer with ItemOnServer2 and checking what happens.

Answer 2

Instead of using an NSDictionary declare feedElement as an NSMutableArray , so something like:

- (NSMutableArray *) convertFeedtoObject:(NSMutableArray*)feed {
    NSMutableArray * _newitems = [[NSMutableArray alloc] init];
    NSMutableArray *feedElement = [[NSMutableArray alloc] init];
    for (int i = 0; i < feed.count; i++) {
        feedElement = feed[i];

        ItemOnServer *newItem = [[ItemOnServer alloc] init];
        newItem.itemtitle = feedElement[@"itemtitle"];
        ...