How to implement Child's delegates in Parent?
Parent.h:
#interface Parent : NSObject
Child.h
#import "Parent.h"
#protocol ChildDelegate <NSObject>
- (void)someMethod;
#end
#interface Child : Parent
I cannot declare Parent's interface to be:
#interface Parent : NSObject<ChildDelegate>
since it need to import "Child.h" and it will be circular import.
How can i solve this?
You should declare protocol conformance in source files (with .m extension).
You can declare Parent class in Parent.h without conformance to ChildDelegate protocol.
#interface Parent : NSObject
And in your Parent.m file you can write something as following.
#import "Child.h"
#interface Parent() <ChildDelegate>
#end
#implementation Parent
// Your implementation code here
#end
Related
I just got started working with delegates.
from some reason I cannot do it, and I see errors.
I tried to do the next code on a new project and it was OK, but when i'm moving this code to my main project I have a few issues.
my NSObject class .h:
#protocol myNSObjectClassDelegate <NSObject>
#required
-(void)doSomething;
#end
#interface GeneralMethods : NSObject
#property (nonatomic,strong) id<myNSObjectClassDelegate> delegate;
#end
my NSObject class .m:
#synthesize delegate;
-(void)SomeMethod {
if ([delegate respondsToSelector:#selector(doSomething)]) {
[delegate doSomething];
}
}
my UIViewController .h
#import "GeneralMethods.h"
#interface view : UIViewController<UIGestureRecognizerDelegate,
UINavigationControllerDelegate,
 UIImagePickerControllerDelegate,
myNSObjectClassDelegate>
The error is here at .h - Cannot find protocol declaration for 'myNSObjectClassDelegate'
my UIViewController .m
-(void)doSomething{
}
What am I doing wrong?
EDIT : I figure it out:
For some reason, at my NSObject class, if I'm moving the #import myUIViewcontroller after this:
#protocol myNSObjectClassDelegate <NSObject>
#required
-(void)doSomething;
#end
the problem solved.
We can't see all the code but after reading some more of the exchanges it looks like dependencies are maybe added out of order. I recommend moving the protocol into its own file and #import'ing it to all the places that use it. This way you definitely will be importing things in the order you expect.
In addition to that, the following property declaration:
#property (nonatomic,strong) id<myNSObjectClassDelegate> delegate;
Delegates should be declared as weak, not strong.
#property (nonatomic,weak) id<myNSObjectClassDelegate> delegate;
The reason is to avoid retain cycles/memory leaks. Typically, though not always the relationship looks like this:
Parent Object (usually Controller) -----STRONG-----> Child (View often)
View Thing ----WEAK--------> delegate (actually the Parent Object)
Now if the relationship is STRONG both ways, releasing the parent from all who own it will not be sufficient to release it since its child also holds an owning relationship to it.
Also you can omit the:
#synthesize delegate;
Auto property synthesis renders this obsolete.
Make sure to import your NSObject class .h. file into your UIViewController's .h file (or wherever you declare the protocol). As it stands, you haven't imported the header that declares the protocol so your view controller has no way of knowing that it exists.
Ex:
#import "FileWithProtocol.h"
#interface MyClass <MyProtocol>
...
#end
In the view controller .h file, try adding this line:
#protocol MyNSObjectClassDelegate;
before
#interface ...
I have following header:
#protocol AttachmentsViewDelegate <NSObject>
#required
- (void)spaceRequestedWithSize:(CGSize)size sender:(AttachmentsView*)sender;
#end
#interface AttachmentsView : UIView
#property id<AttachmentsViewDelegate> delegate;
#property NSArray *attachments;
- (void)takePicture;
- (void)deletePictures;
#end
Doesn't work because inside #protocol I reference to AttachmentsView and it's not declared yet.
If I move #protocol below #interface - I have another problem, because delegate property doesn't know about #protocol.
I know I can use id, UIView for types, but to keep it "strongly typed", what can I do? I really prefer not to break it down into 2 files. Any other options/suggestions?
Use #class to forward-declare AttachmentsView like so:
#class AttachmentsView;
#protocol AttachmentsViewDelegate <NSObject>
// Protocol method declarations...
#end
Alternatively, use #protocol to forward-declare the protocol:
#protocol AttachementsViewDelegate
#interface AttachmentsView : UIView
// Ivar, method, and property declarations...
#property id<AttachmentsViewDelegate> delegate;
#end
just write:
#class AttachmentsView;
on top of the file.
In case you wish to declare the class first, and then the protocol, write first:
#protocol AttachmentsViewDelegate;
on top of the file.
//Super class .h file
#interface MySuperClass : NSObject
#end
//Super class .m file
#interface MySuperClass ()
#property (nonatomic, strong) UITextField *emailField;
#end
#implementation MySuperClass
-(void)accessMyEmailField {
NSLog(#"My super email: %#", self.emailField.text);
}
#end
// ********** my subclass *******
//Subclass .h file
#interface MySubClass : MySuperClass
#end
//SubClass .m file
#interface MySubClass ()
#end
#implementation MySubClass
-(void)myEmail {
NSLog(#"My subclass email: %#", self.emailField.text);
}
-(void)setMyEmailFromSubclass{
self.emailField.Text = #"email#gmail.com"
}
#end
How do i access emailField in -(void)myEmail method.
How do i set email in Subclass -(void)setMyEmailFromSubclass; , and access it in super class accessMyEmailField
You can put accessors to these properties in a second header file, and import that file on a 'need-to-know' basis..
eg
mySuperClass+undocumentedProperties.h
#import "mySuperClass.h"
#interface mySuperClass(undocumentedProperties)
#property (nonatomic, strong) UITextField *emailField;
#end
mySuperClass.m
#import "mySuperClass+undocumentedProperties.h"
#interface mySuperClass()
///stuff that truly will be private to this class only
// self.emailField is no longer declared here..
#end
#implementation mySuperClass
#synthesize emailField; //(not really needed anymore)
/// etc, all your code unaltered
#end
mySubclass.h
#import "mySuperClass.h"
#interface mySubclass:mySuperClass
///some stuff
#end
mySubclass.m
#import "mySubclass.h"
#import "mySuperClass+undocumentedProperties.h"
#implementation
//off you go, this class is now 'aware' of this secret inherited property..
#end
obviously MySuperClass.m will have to import this .h file as well as its default one (or actually instead of, the default one is built in to this one), but your subclasses can import it too (directly into their .m file, so these properties remain private to the class. This is not a proper category because there is no corresponding mySuperClass+undocumentedProperties.m file (if you tried that you could not synthesize the backing iVars for these secret properties. Enjoy :)
Copy the private interface portion of the methods you want from your superclass - or in other words, in your Subclass.m file you would put:
#interface MySuperClass ()
#property (nonatomic, strong) UITextField *emailField;
#end
( place it above the existing #interface MySubClass () code )
Now your subclass knows that method exists in the superclass and can use it, but you are not exposing it to anyone else.
The whole point of private properties is exactly that and you should not want to access them. Because they are private they can change or be removed thus breaking the subclass that relies on them.
That being said they are not really private, just not "published". The can be called because Objective-C is a run-time dynamic language.
i've worked with delegation before. i know how to create delegation from a superview to a subview class. however, i'm trying to do it the opposite way using the same approach but it's not working! is delegation meant only to work one way or is there a way/trick to use it as a two way communication between the classes? I'm receiving an error at the parent/superview .h class which is:
Cannot find protocol definition for 'SubViewControllerDelegate'
my code goes like this:
subview.h
#import <UIKit/UIKit.h>
#import "SuperViewController.h"
#protocol SubViewControllerDelegate <NSObject>
- (void)someMethod:(NSData *)data;
#end
#interface SubViewController : UIViewController
#property (weak, nonatomic) id <SubViewControllerDelegate> delegate;
#end
subview.m:
[self.delegate someMethod:data];
SuperView.h
#import <UIKit/UIKit.h>
#import "SubViewController.h"
#interface SuperViewController : UIViewController <SubViewControllerDelegate>
#end
SuperView.m:
#pragma mark - SubView Controller Delegate Methods
- (void)someMethod:(NSData *)data{
NSLog(#"%#", data);
}
am i doing anything wrong or missing out anything?
You have an "import-cycle", because "SuperViewController.h" imports "SubViewController.h" and vice versa.
Removing the #import "SuperViewController.h" in "SubViewController.h"
should solve the problem.
If you really need that class to be declared in "SubViewController.h", use
#class SuperViewController; to avoid the import-cycle.
Remark: The <SubViewControllerDelegate> protocol declaration is probably not
needed in the public interface "SuperViewController.h" at all.
In "SuperViewController.h", declare the class as
#interface SuperViewController : UIViewController
In "SuperViewController.m", define a class extension with the protocol:
#interface SuperViewController () <SubViewControllerDelegate>
#end
I have started new iOS project and have added only one property in ViewControler header file. but it gives me error:
expected specifier-qualifier-list before 'property'
here is the code:
#import <UIKit/UIKit.h>
#interface QuoteGenViewController : UIViewController {
#property (retain) NSArray *myQuotes;
}
#end
Here the general structure of a class interface
#interface Class : Superclass
{
// Instance variable declarations.
// Theirs definition could be omitted since you can declare them
// in the implementation block or synthesize them using declared properties.
}
// Method and property declarations.
#end
Since a property provides a simple way to declare and implement an object’s accessor methods (getter/setter), you need to put them in the Method and property declarations section.
I really suggest to read ocDefiningClasses doc for this.
Hope that helps.
Your code should look like this:
#import <UIKit/UIKit.h>
#interface QuoteGenViewController : UIViewController {
}
#property (retain) NSArray *myQuotes;
#end