I have utilized subclassing of PFObject for a few classes in my code including the following classes:
MGRound:PFObject - a class that represents a golf round
MGCurrentRound:MGRound - a singleton class that holds data for the current round being entered. As you can see it is a subclass of MGRound
When I try to instantiate an object of class MGRound using [MGRound object] the object that I am getting is of the class MGCurrentRound.
Has anyone else run into this? Any suggestions?
The issue noted above was not my problem. I had to use the valueForKey method because the objects were PFObjects, not my subclasses. I was trying to use dot notation was which incorrect.
Related
I am using Cocos3D and this function give me a 'may not respond' warning:
[CClayer.CC3scene someFunctionFromCC3scene];
I know one way to resolve this is to have a Function in CCLayer to make CC3scene call someFunctionFromCC3scene. But is there any other way to do this? Thanks!
More likely you're not importing the corresponding header. For example #import "CC3Scene.h". I suppose this can happen if the return type of the CC3scene property is id instead of the actual class.
Or the compiler is correct about this and it will crash with "does not respond to selector" when you run it. In that case CC3Scene does not implement the someFunctionFromCC3scene selector. Check spelling and parameters, and of course that the class actually implements that selector and has it declared in the #interface.
From the look of your example, there are several things that might be going wrong:
You might be confusing CCLayer with CC3Layer. CC3Layer is a subclass of CCLayer that supports displaying a 3D scene. Be sure you are instantiating a CC3Layer.
If you really are using a CC3Layer and the CC3Scene property (which is actually cc3Scene) is returning an instance of CC3Scene, then, as LearnCocos2D indicates, verify that the method you are invoking actually exists in the CC3Scene class. If you provide the specific method name here, then I can provide further help.
If the someFunctionFromCC3Scene is actually defined and implemented in your custom subclass, then you should cast the CC3Scene instance to your custom subclass before invoking that method:
[((MyCC3Scene*)aCC3Layer.cc3Scene) someFunctionFromMyCC3Scene];
...Bill
SquareGeo, TriangleGeo is drived from Geo class.
Each of SquareGeo, TriangleGeo classes have drawMe methods with same parameters but different content.
I wantto call drawMe from the base class is Geo
but, issue Navigator says me a warning:
"Instance method '-drawMe' not found (return type defaults to 'id')"
in conclusion:
How can I call a method from Parent that is only defined all its child Classes.
shall I avoid warning ? should I use protocols ?
looking something like this:
[sub drawMe]; //not super
any idea ? (please do not refer me to java examples.only objectC knowhow)
Thats the beautiful thing about inheritance, you declare the method in the parent, and implement it in the children, and the underlying system handles calling the "correct" version of the method depending on what type of class the instance actually is.
The easiest way to overcome this is to provide an empty implementation in the parent class.
If you want to ensure that subclasses do provide their own implementation then you can add an exception to the base class' method
#implementation Base
- (void)drawMe;
{
[NSException raise:NSInternalInconsistencyException
format:#"You must override %# in a subclass", NSStringFromSelector(_cmd)];
}
I have a problem with creating my own subclass of NSData, which I want to have a custom description method. Even creating a dummy NSData subclass:
#interface MyData : NSData {}
#end
and
#implementation MyData
#end
and using it results in weird bugs (the function that uses it never exits, and control somehow returns to the run loop). I thought that maybe I am responsible for rewriting the designated initializers of NSData (calling the super implementation), but none is mentioned in the doc. So:
what are the designated initializers of NSData?
what is the bare minimum I need to write for a dummy subclass of NSData?
Making an NSData subclass is difficult because (as drewag noted) it is a member of a class cluster. From the Binary Data Programming Guide:
...data objects are not actual instances of the NSData or NSMutableData classes but instead are instances of one of their private subclasses.
When you do [[NSData alloc] initWith...] you don't get back an NSData; you probably get back an NSConcreteData. The extraordinary Cocoa With Love has a discussion and demonstration of subclassing class clusters.
The best (and most idiomatic) option is probably composition: your custom class should simply contain an NSData ivar, and implement a description method that operates on that enclosed object.
While drewag's response is technically correct, this is a dangerous technique to use on Cocoa classes; it will override the description method of every NSData object in the program, whether you create it directly or not.
In the specific case of the description method this may be okay, but for another method more likely to be relied upon by other objects in the framework, it could cause large, hard-to-trace problems. You should only do this if you are sure that there is no other way.
It would be far better to create a category and method with a prefix:
#interface NSData (FX_Description)
- (NSString *)FX_description;
#end
The Apple docs specifically mention this category-override technique and advise against it:
Because the methods declared in a category are added to an existing class, you need to be very careful about method names.
If the name of a method declared in a category is the same as a method in the original class, or a method in another category on the same class (or even a superclass), the behavior is undefined as to which method implementation is used at runtime.
An earlier version of the docs went on to say:
The very presence of some category methods may cause behavior changes across all frameworks. For example, if you override the windowWillClose: delegate method in a category on NSObject, all window delegates in your program then respond using the category method; the behavior of all your instances of NSWindow may change. Categories you add on a framework class may cause mysterious changes in behavior and lead to crashes. [Emphasis mine.]
If all you want is to override a single function "description" consider using a "Category" instead:
#interface NSData (MyData)
-(NSString*)description;
#end
#implimentation NSData (MyData)
-(NSString*)description
{
return #"something";
}
#end
Then, you can use this function on any instance of NSData.
It is very difficult to subclass NSData because it is a "Class Cluster." The public API treats it as one class, but in reality it is a collection of hidden subclasses. You can research overriding a class cluster, but it is almost never needed. Another option is to create your "MyData" class with NSData as a member variable instead of using a subclass.
I have a data model which has two entities in a relationship of one to many.
Each entity has a class that is subclassed from NSManagedObject.
I get the relation set for the one entity and walk it casting each set member to the specific subclass as I enumerate the collection.
When I do
NSLog(#"My Entity: %#", myEntityInstance);
It logs but does not call my subclass's method for:
- (NSString*) description
It does call if I send:
NSLog(#"My Entity: %#", [myEntityInstance description]);
Any ideas what is being called and why description has to be manually called?
Thanks!
If a class instance responds to descriptionWithLocale:, then NSLog will use that instead. Although descriptionWithLocale: does not appear in NSManagedObject's list of instance methods, it could possibly still be implemented.
Try overriding descriptionWithLocale: and see if that makes a difference.
- (NSString *) descriptionWithLocale:(id) locale
{
return #"my description";
}
I've never seen that. I don't think it's a NSManagedObject behavior. You might log the class before making the call to make sure your instance is of the class you think it is.
Might be two years or so late to the game, but for the benefit of others, I had this problem tonight. The cause was that, while I had made NSManagedObject subclasses for my entities, one of the entities in the CoreData Modler had it's "Class" set back to NSManagedObject instead of the custom subclass.
It didn't matter what I put into -description in my subclass files, because the objects were coming out of the Context as NSManagedObjects instead of my custom subclass.
Putting the subclass name back in the Entity Inspector in the Xcode Coredata Model Editor fixed it.
Stuck on what I figure is simple thing here. Basically I need to pass a pointer to an object as an argument into an instance method of another class. Said differently: I have a class that creates "Things" and I have an instance of another class that I want to receive the "Things."
Working with Cocos2D frameworks. The Things are a custom subclass of CCSprite, and the instance that receives them is a CCLayer.
I figure I'm misunderstanding something basic about ivars or maybe properties here. Any pointers in the right direction would be appreciated.
Here's the interface for ThingLayer, which should receive the "thing":
#interface ThingLayer: CCLayer {
CCTextureAtlas *textureAtlas;
ThingLayer *thingLayer;
NSMutableArray *ThingsArray;
}
- moveThingtoLayer:(Thing*)athing;
#end
And here's how I'm trying to message to the instance, from outside the class:
[ThingLayer moveThingtoLayer:thing];
I realize I'm asking the class here, not the instance... which is giving me "may not respond to..." errors. But this isn't working either (asking name of instance)...
[thingLayer moveThingtoLayer:thing];
Any obvious answers?
Looks like you should have
ThingLayer *thingLayer = [[ThingLayer alloc] init];
[thingLayer moveThingtoLayer: thing];
As a side thought, you most likely want to init a new thing in thingLayer so that instance owns the Thing, and release thing after calling moveThingToLayer.