I am getting the following error:
"-[Order items]: unrecognized selector sent to instance 0x6b5f240"
I do have a class called Order, which looks like this:
Order.h
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
#class OrderItem;
#interface Order : NSManagedObject {
#private
}
#property (nonatomic, retain) NSNumber * orderID;
#property (nonatomic, retain) NSDate * date;
#property (nonatomic, retain) NSNumber * orderCode;
#property (nonatomic, retain) NSSet* items;
#end
Order.m
#import "Order.h"
#import "OrderItem.h"
#implementation Order
#dynamic orderID;
#dynamic date;
#dynamic orderCode;
#dynamic items;
...
It doesn't extend any sort of class which has an "items" method, if I'm reading that correctly?
Is there any other reason I would be getting such an error. To add to the madness, this project is copied directly from a previous project, with some minor edits. I've done text comparisons on every single class in both projects and there are no differences other than the cosmetic changes I've made.
#dynamic items tells the compiler that you will be providing the methods for items.
Since this was working in a previous project, it must have had the following method somewhere in the .m file:
- (NSSet *)items {
// Appropriate code
}
If you do not want to provide your own custom getter like this, then change #dynamic items to #synthesize items and the compiler will generate one for you.
For more details, see the Declared Properties section of The Objective-C Programming Language provided by Apple here: https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProperties.html
EDIT
While everything above still applies to a normal object (and may still apply here), I just noticed that this is a subclass of NSManagedObject.
In your old data model there was probably a relationship called items and therefore the appropriate methods were provided by NSManagedObject and #dynamic was appropriate to prevent compiler warnings.
If in your new data model there is no relationship named items, then the methods will not be generated and it will cause the problem that you are getting here.
Related
Since upgrading to Xcode 5.1, I'm starting to see the following warning in some code my project uses. I'm trying to figure out what it means.
Warning: Auto property synthesis will not synthesize property 'responseHeader' because it is 'readwrite' but it will be synthesized 'readonly' via another property
The code where it's occurring, in the .m file:
#interface S3Response ()
#property (nonatomic, readwrite, retain) NSDictionary *responseHeader;
#end
The previous declaration of the property, in the .h file:
#property (nonatomic, readonly) NSDictionary *responseHeader;
There is no #synthesize statement for that property, nor are responseHeader or setResponseHeader defined as methods. There is however an explicit definition of an ivar named responseHeader.
Seems pretty straightforward to me: property is declared as read-only for users of the class, but read-write locally so the class can set it.
What does this warning mean, and what should I do about it?
That code seems to be from the AWS SDK for iOS,
and S3Response is a subclass of AmazonServiceResponse.
The public AmazonServiceResponse interface defines a read-only property
#interface AmazonServiceResponse:NSObject
// ...
#property (nonatomic, readonly) NSDictionary *responseHeader;
#end
which is redefined as read-write in a class extension in the implementation file:
#interface AmazonServiceResponse ()
#property (nonatomic, readwrite, retain) NSDictionary *responseHeader;
#end
Now the subclass S3Response also wants read-write access to this property,
and therefore also defines in the class extension of its implementation file:
#interface S3Response ()
#property (nonatomic, readwrite, retain) NSDictionary *responseHeader;
#end
The compiler complains because – when compiling "S3Response.m" – it does not know
that a setter for the property exists in the superclass (it does not read
the implementation file of the superclass at that point). Also the compiler cannot
simply synthesize a setter in the subclass, because it cannot not know that the
property is backed-up by an instance variable in the superclass.
But you know that a setter will be generated, so you can remove the warning by
adding a #dynamic declaration to the subclass implementation:
#implementation S3Response
#dynamic responseHeader;
...
#dynamic is a "promise" to the compiler that all necessary accessor methods will
be available at runtime.
The problem here is as follows.
By default, if don't write ownership (weak/retain/strong/assign) explicitly, xCode will check the type automatically. So in case of NSDictionary it will be strong. Thus, in interface you will have
#property (nonatomic, readonly, strong) NSDictionary *responseHeader;
Then it will be contradict you private implementation definition
#property (nonatomic, readwrite, retain) NSDictionary *responseHeader;
Compilator doesn't match strong and retain under property synthesizing though it is formally the same thing.
To cure situation you can write retain in both cases, or more correct, you should not write retain at all. It will be strong by default in both definitions.
I may not have worded the question right, but I am not sure if what I am asking makes 100% so here goes:-)
In Xcode you can set a #class (name of class) above the #interface in the header file.
Is this the same as changing the the UIViewController in the name of the class? See code below:
So is this the same -
#class CoreDataClass;
#interface FlipsideViewController : UIViewController <UITableViewDataSource, UITableViewDelegate>
{
}
//This file declares the UITableView
#property (nonatomic, retain) IBOutlet UITableView *mainTableView;
#property (nonatomic, retain) CoreDataClass *cdc;
As this:
#interface FlipsideViewController : CoreDataClass <UITableViewDataSource, UITableViewDelegate>
{
}
//This file declares the UITableView
#property (nonatomic, retain) IBOutlet UITableView *mainTableView;
#property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
#end
??
If this is not the same, how is it different and what are advantages to the different implementation?
The Difference is only really asked if they are similar:-)
#class is not used to create a class, but to forward declare another one. See this question for a good explanation.
They are not the same at all. The first case is a 'forward declaration' - you are telling the compiler that the class CoreDataClass exists, so that you can refer to it in your header file without actually importing the files that define it.
The second case, you are declaring that FlipsideViewController is a subclass of CoreDataClass, and inherits all its methods and instance variables.
They're not even related. The difference is that the superclass ("parent" class) of your view controller will be different (and this can lead to nice unrecognized selector errors...). Forward-declaring a class using the #class keyword is just a convenient way of referring to a class when one doesn't want to import a whole framework header hierarch just in order to refer to one class. I. e., if you don't need to know anyting about a class except that it exists, you can use this keyword. Be careful, however, if you maks heavy use of the class - in those cases, the class forward-declaration is not considered a good solution.
In first case when you use #class it's inform XCode that you will be using CoreDataClass somewhere and you will #import header for example in .m file, in second case you're inherit from CoreDataClass (you will get access to all public and protected properties)
I've attempted to compile, but every time I do, one method throws a strange "expected a type" error. I have a method in the header:
-(ANObject *)generateSomethingForSomethingElse:(NSString *)somethingElse;
The error points at the return type for this method. I've imported ANObject into the header using #import "ANObject.h" and ANObject is compiling fine..
Why is this happening?
This is to do with the order that the source files are compiled in. You are already probably aware that you can't call a method before it is defined (see below pseudocode):
var value = someMethod();
function someMethod()
{
...
}
This would cause a compile-time error because someMethod() has not yet been defined. The same is true of classes. Classes are compiled one after the other by the compiler.
So, if you imagine all the classes being put into a giant file before compilation, you might be able to already see the issue. Let's look at the Ship and BoatYard class:
#interface BoatYard : NSObject
#property (nonatomic, retain) Ship* currentShip;
#end
#interface Ship : NSObject
#property (nonatomic, retain) NSString* name;
#property (nonatomic, assign) float weight;
#end
Once again, because the Ship class has not yet been defined, we can't refer to it yet. Solving this particular problem is pretty simple; change the compilation order and compile. I'm sure you're familliar with this screen in XCode:
But are you aware that you can drag the files up and down in the list? This changes the order that the files will be compiled in. Therefore, just move the Ship class above the BoatYard class, and all is good.
But, what if you don't want to do that, or more importantly, what if there is a circular relationship between the two objects? Let's increase the complexity of that object diagram by adding a reference to the current BoatYard that the Ship is in:
#interface BoatYard : NSObject
#property (nonatomic, retain) Ship* currentShip;
#end
#interface Ship : NSObject
#property (nonatomic, retain) BoatYard* currentBoatYard;
#property (nonatomic, retain) NSString* name;
#property (nonatomic, assign) float weight;
#end
Oh dear, now we have a problem. These two can't be compiled side-by-side. We need a way to inform the compiler that the Ship* class really does exist. And this is why the #class keyword is so handy.
To put it in layman's terms, you're saying, "Trust me man, Ship really does exist, and you'll see it really soon". To put it all together:
#class Ship;
#interface BoatYard : NSObject
#property (nonatomic, retain) Ship* currentShip;
#end
#interface Ship : NSObject
#property (nonatomic, retain) BoatYard* currentBoatYard;
#property (nonatomic, retain) NSString* name;
#property (nonatomic, assign) float weight;
#end
Now the compiler knows as it compiles BoatYard, that a Ship class definition will soon appear. Of course, if it doesn't, the compilation will still succeed.
All the #class keyword does however is inform the compiler that the class will soon come along. It is not a replacement for #import. You still must import the header file, or you will not have access to any of the class internals:
#class Ship
-(void) example
{
Ship* newShip = [[Ship alloc] init];
}
This cannot work, and will fail with an error message saying that Ship is a forward declaration. Once you #import "Ship.h", then you will be able to create the instance of the object.
I found this error hapenning when there is circular dependency on the headers. Check if the .h file where you declare this method is imported in ANObject.h
You basically add
#class ANObject;
before #interface!
So, for some reason I was getting this error while trying to set a method with an enum type in the parameters. Like so:
- (void)foo:(MyEnumVariable)enumVariable;
I had previously used it like this and never had an issue but now I did. I checked for circular dependency and could find none. I also checked for typos multiple times and no dice. What ended up solving my issue was to adding 'enum' before I wanted to access the variable. Like so:
- (void)foo:(enum MyEnumVariable)enumVariable;
{
enum MyEnumVariable anotherEnumVariable;
}
Usually when I see an error like this it's because I have a typo on a previous line, such as an extra or missing parenthesis or something.
It may sound stupid, but wrong shelling or wrong use of uppercase/lowercase letterwrong case this.
I got this message, when the variable type was misspelled. See below this below
e.g.
-(void)takeSimulatorSafePhotoWithPopoverFrame:(GCRect)popoverFrame {
instead of.....
-(void)takeSimulatorSafePhotoWithPopoverFrame:(CGRect)popoverFrame {
Strangely enough, changing the order of my imports has fixed this in the past... Try moving the import to the bottom after all your other imports.
I solved it by adding #class class_name to the .h file
What is the #private for in the file generated by Core Data below? I know what #private means in Objective-C, but there are not instance variables listed after it, so can't I just take it out?
//
// Event.h
//
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
#interface Event : NSManagedObject {
#private
}
#property (nonatomic, retain) NSDate * timestamp;
#end
//
// Event.m
//
#import "Event.h"
#implementation Event
#dynamic id;
#end
You can safely take it out, it won't change the semantics of your class. If you're not statisfied with what XCode generates for you (though it's a reasonable default), I'd suggest you take a look at https://github.com/rentzsch/mogenerator.
You can, but it doesn't hurt. If you generate the model again it will just put it back.
Xcode now defaults to generating classes with #private for instance variables, which you are supposed to declare in case you need them. You can safely remove that #private since, as you’ve already noticed, there are no instance variables. In fact, that class declaration is equivalent to
#interface Event : NSManagedObject
#property (nonatomic, retain) NSDate * timestamp;
#end
I want to define one protocol with few properties and need to use those properties in another NSObject subclass. Please give me link or example code. I need that to work with 10.5.
Thanks
PLEASE CHECK THE FOLLOWING SAMPLE CODE
#protocol MyProtocol
#property (nonatomic, readonly) id someObject;
#property (nonatomic, getter=isAlive) BOOL alive;
#end
#import "MyProtocol.h"
#interface MyCustomClass : NSObject <MyProtocol>{
}
#end
#import "MyCustomClass.h"
#implementation MyCustomClass
#synthesize someObject,alive;
/*
- (id)someObject {
return nil;
}
- (BOOL)isAlive {
return YES;
}
- (void)setAlive:(BOOL)aBOOL {
}
*/
#end
**Added:
Compling code with x86_64 architecture works fine. But error if i'll change the architecture to i386, then i am getting following warnings:
MyCustomClass.m:13: error: synthesized property 'someObject' must either be named the same as a compatible ivar or must explicitly name an ivar
error: synthesized property 'alive' must either be named the same as a compatible ivar or must explicitly name an ivar
I just want to know why it is working in x86_64 with #synthesize and not in i386.**
#property just says to the compiler that the class is expected to define the methods to match that property.
#protocol MyProtocol
#property (nonatomic, readonly) id someObject;
#property (nonatomic, getter=isAlive) BOOL alive;
#end
Anything implementing that protocol will now need to have
- (id)someObject;
- (BOOL)isAlive;
- (void)setAlive:(BOOL)aBOOL;
I think the things you're dealing with are primarily side effects of the introduction of Objective-C 2.0. It lets you do things like declare properties without also defining instance vars. But (as you have discovered), it is only x86_64 and post-10.5 compatible.