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
Related
I have read in iOS Programming Fundamentals by Matt Neuberg that instance variables are protected, meaning that other classes, except for subclasses of this one, can't see them.
I have a parent class A where I define an ivar list.
(A.m)
#interface A ()
#end
#implementation A
{
NSArray *list;
}
#end
Class B extends A (B.h)
#import "A.h"
#interface B:A
#end
(B.m)
#interface B ()
#end
#implementation B
list =
...
#end
I want to use ivar list in child class B but the compiler doesn't see that the was reference declared in the parent class. I have tried explicitly using #protected but that doesn't work. I don't want to expose ivar list on the public interface. It's an internal structure that is a common element of all subclasses. How can I do this?
Instance variables that are declared outside a class's public interface (in other words, the #interface section) are private by default. You can add a visibility modifier to the declaration to change the visibility of one or more ivars like so:
#implementation A
{
NSNumber *_ivarWithDefaultVisibility;
#protected
NSArray *_list;
NSString *_anotherIvarWithProtectedVisibility;
}
(Note that according to Apple's Cocoa coding guidelines, ivar names should be prefixed with an underscore.)
This is not the usual way to implement protected properties in ObjC. (#protected and #private are very seldom used in Cocoa.) First, use a property, not an ivar. It will make it much cleaner. Declare it this way:
A.h
#interface A : NSObject
// Public interface goes here
#end
A.m
// Declare the property in a class extension inside the implementation file.
// This is the idiomatic way to create a "private" property.
#interface A ()
#property (nonatomic, readwrite, strong) NSArray *list;
#end
A+protected.h
// Enumerated any methods that should be accessible to subclasses here.
// Properties are just a special way of defining methods.
// The word "Protected" is just a category name.
#interface A (Protected)
#property (nonatomic, readwrite, strong) NSArray *list;
#end
B.h
#import "A.h"
#interface B : A
...
#end
B.m
#import "B.h"
#import "A+protected.h"
// ... now you can use self.list ...
This approach allows you to create any kind of "protected" method, not just properties, and is also the technique used to create "friend" classes.
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 want to access super class iBoutlets objetcs in my subclass. Is that possible?. I am trying in the following way but am always getting nil.
Here is my code:
My super class
#import <UIKit/UIKit.h>
#interface SuperClassA : UIViewController {
}
#property (weak, nonatomic, getter=getDummyView) IBOutlet UIView *dummyView;
#end
#implementation SuperClassA
- (void)viewDidLoad {
[super viewDidLoad];
SubClassB *obj = [SubClassB new];
[obj printSuperClassiBouletObject];
}
#end
my subclass:
#import <UIKit/UIKit.h>
#interface SubClassB : SuperClassA {
}
#end
#implementation SubClassB
-(void)printSuperClassiBouletObject
{
NSLog(#"view: %#", [self getDummyView]);
}
#end
The above code gives me nil value always. Any idea how to get the actual iBoutlet object?. But when i pass the iBoutlet as an function argument then the object was not nil. In the super class i tried strong property, using #synthesize in implementation file but no helps. Any help that really might be appreciated.
My guess is that the problem is here:
SubClassB *obj = [SubClassB new];
[obj printSuperClassiBouletObject];
New will use default initializer, that will try to load nib with your class name, which is SubClassB. Do you have SubClassB.xib that set the outlet your project? If not, then SubClassB will be initialized with empty properties, by the default objc initializer.
Try this:
SubClassB *obj = [[SubClassB alloc] initWithNibName:#"SuperClassA"]; //or xib name that SuperClassA uses to initialize
There's nothing special about IBOutlet relative to the scope rules. You can inherit any property from super by including its declaration in the subclass. The simple way to do this is by placing those property declarations in the superclass's public interface (in superclass.h). Since we know that the subclass must import that, we know that everything in there will be available to the subclass.
A more complicated arrangement is required if you'd like the subclass to access the property but not other classes. These "protected" declarations need to go into a third header file that only the super and subclass import.
In other words... (simple case):
// MySuper.h
#interface MySuper : NSObject
#property (weak,nonatomic) IBOutlet UIView *someOutlet;
#end
// MySub.h
#import "MySuper.h"
#interface MySub : MySuper
// stuff for my sub
#end
Now both MySuper and MySub can refer to someOutlet
For "protected", something like this:
// MySuper.h
#interface MySuper : NSObject
// only public stuff here
#end
// MySuper-protected.h
#interface MySuper ()
#property (weak,nonatomic) IBOutlet UIView *someOutlet;
#end
// MySuper.m
#import "MySuper.h"
#import "MySuper-protected.h"
// MySub.h
// same as simple case
// MySub.m
#import "MySub.h"
#import "MySuper-protected.h"
Finally, i was able to achieve this by using this way!!!!
In my subclass i changed the method to:
-(void)printSuperClassiBouletObject:(SuperClassA*)superClassObj
and in my super class i am calling this way:
SubClassB *obj = [SubClassB new];
[obj printSuperClassiBouletObject:self];
And in my subclass i was access the super class objects and its variable from the super class instance it self.
Thanks for all the help !!!!!! :-)
I have a UIView subclass called NumberPickerView. I'm writing a delegate method for it. The compiler won't let me pass an instance of NumberPickerView as an parameter in that method. What am I missing?
#protocol NumberPickerViewDelegate
-(void) numberPickerDidChangeSelection:(NumberPickerView *)numberPickerView;
//error: expected a type
#end
#interface NumberPickerView : UIView <UIScrollViewDelegate> {
id <NumberPickerViewDelegate> delegate;
}
Actually it CAN. At that point compiler doesn't know about NumberPickerView class
#class NumberPickerView;
add it over protocol declaration to let compiler know about that class... It's called forward declaration.
For better understanding check this out:
iPhone+Difference Between writing #classname & #import"classname.h" in Xcode
OR
move protocol declaration below the class NumberPickerView definition but in that case you should also add at top:
#protocol NumberPickerViewDelegate;
Not to get warnings using id<NumberPickerViewDelegate>delegate
You can change parameter type to id instead of NumberPickerView * and pass any class object afterword as bellow
#protocol NumberPickerViewDelegate
-(void) numberPickerDidChangeSelection:(id)numberPickerView;
#end
#interface NumberPickerView : UIView <UIScrollViewDelegate> {
id <NumberPickerViewDelegate> delegate;
}
I am attempting to create an abstract class and inherit some of its properties in a subclass. If I leave the properties in the abstract class' header file, all of the properties are accessible. The problem is that the instance of the subclass can also access those properties, which is not always desirable in my case.
For instance, I have a delegate in my abstract class that sends down button presses to its sub class. I realize that this may not be the best way of structuring inheritance, so other suggestions are welcome. However, I would still like to know how my subclass can inherit some properties from its superclass without making all of those properties available in its instance. Thanks in advance!
Here is some example code below:
#interface AbstractClass : UIView
#property (nonatomic, strong) id<ButtonDelegate>buttonDelegate;
#end
…
#protocol ButtonDelegate
#required
- (void) buttonWasPressed;
#end
…
#interface SubClass() <ButtonDelegate>
- (id)init {
self = [super init];
if (self) {
self.buttonDelegate = self;
}
return self;
}
-(void) buttonWasPressed {
[self doSomething];
}
…
#implementation ViewController
- (void)viewDidLoad {
SubClass *subClass = [[SubClass alloc] init];
subClass.buttonDelegate = self; // THIS IS NOT DESIRABLE
}
Do like UIGestureRecognizer does.
All public properties and methods goes into UIGestureRecognizer.h
All protected properties and methods goes into UIGestureRecognizerSubclass.h.
Only import this in the *.m-files. Never include it in any public header.
All private properties and methods goes into *.m-files. Use the #interface ClassName ()
Example https://gist.github.com/hfossli/8041396
how to my subclass can inherit some properties from its superclass
without making all of those properties available in its instance
What is the problem with this?
#import <Foundation/Foundation.h>
#interface Animal : NSObject
{
#protected
NSString *name; // default access. Only visible to subclasses.
}
#end
#implementation Animal
-(NSString*)description {
return name;
}
#end
#interface Cow : Animal
#end
#implementation Cow
-(id)init {
self=[super init];
if (self){
name = #"cow";
}
return self;
}
#end
int main(int argc, char *argv[]) {
#autoreleasepool {
Cow *cow = [Cow new];
NSLog(#"%#", cow); // prints the name through internal access
// error accessing from the outside: NSLog(#"%#", cow.name);
Animal *animal = [Animal new];
// error accessing from the outside: NSLog(#"%#", animal.name);
}
}
Maybe I misunderstood the question, you say
Creating properties only visible to subclass in Objective-C
and then
The problem is that the instance of the subclass can also access those
properties
Which one is it?
Create an empty category on top of your implementation file (.m):
#interface AbstractClass()
#property (nonatomic, strong) id<ButtonDelegate>buttonDelegate;
#end
In that way, your subclass will inherit and can access that property, but not other external classes because it's not in the header.
I don't think there is any way to achieve this using property declaration.
Either a property be visible for all (declared in .h file) or it will be invisible for all (declared in .m file using category)
I guess one way is declaring public/protected variable in .h file class declaration:
#interface AbstractClass : UIView {
...
id<ButtonDelegate>buttonDelegate;
...
}
#end
I am not sure about this, but give a try.
I see one approach that can fit your problem, however, it is pretty rude. Use Antonio's suggestion and create the private category with the property. As you've mentioned, it's scope is limited to the .m file. So you can put your subclasses into that file. This will be hard to read the code if subclasses are huge, but this is the only way for you as far as I understand.
EDIT: well, I have another solution. Copy
#property (nonatomic, strong) id<ButtonDelegate>buttonDelegate;
to all your subclasses. This will give you a warning about the absence of the property's #synthesize, but should work. I'd prefer this, if subclasses wont be changed or added often.
Let me describe how it would work.
We add a property into the Abstract class, and it is hidden for all (even for subclasses):
// .m file
#interface Abstract ()
#property (nonatomic, strong) id<ButtonDelegate> buttonDelegate;
#end
#implementation Abstract
#synthsize buttonDelegate;
#end;
But due to runtime features of Objective-C we still can call for that property, and there will not be any runtime error, only compiler warning.
To get rid of that warning and to add an ability to autocomplete, we add property without #synthsize into all subclasses:
#interface MySubclass : Abstract
#property (nonatomic, strong) id<ButtonDelegate> buttonDelegate;
#end
This will tell the compiler that there is such a property somewhere. There will be also one warning about the absence of #synthesize, but Xcode will still could autocomplete if you write something like
MySubclass *subclass = ...
subclass.butto...
It can not be done. There is no private or protected in objective-c. Stuff declared in the .m file "private" interface is only visible to that class and not in any subclass. Also you can always use your "private" properties/methods from outside if you want, although it would be bad practice to do so.