I have created a very basic Objective-C class.
MyClass.h
#interface MyClass: NSObject
#end
MyClass.m
#import "MyClass.h"
#interface MyClass()
#end
#implementation MyClass: NSObject {
NSMutableArray* _myArray;
}
#end
Xcode is showing the following warning on the #implementation line:
Class implementation may not have super class
The warning goes away if I remove the NSMutableArray* _myArray; line.
What does this warning mean? What am I doing wrong?
Delete NSObject in the implementation part. The super class has to be specified only in the interface.
#implementation MyClass {
NSMutableArray* _myArray;
}
#end
#implementation MyClass: NSObject
You're not supposed to inherit from NSObject in the implementation.
you already got it in the #interface MyClass: NSObject
Related
I have a class written in Swift where I've defined a protocol:
protocol PhotoIngestionDelegate {
func pictureTaken()
}
I am trying to have a class (CameraViewController) written in Objective-C conform to this protocol.
CameraViewController.h:
#import <GSSDK/GSSDK.h>
#protocol PhotoIngestionDelegate;
#interface CameraViewController : GSKCameraViewController <PhotoIngestionDelegate>
#end
CameraViewController.m:
#import "CameraViewController.h"
#import <GSSDK/GSSDK.h>
#import "EditFrameViewController.h"
#import "Scan.h"
#interface CameraViewController<PhotoIngestionDelegate> ()
#property (nonatomic, strong) UIView *toolbar;
#property (nonatomic, strong) UIButton *cameraButton;
#end
#implementation CameraViewController
...
The implementation in CameraViewController.m continues, but I cut it off to keep it brief. I know that I need to define the function pictureTaken() in CameraViewController.m, but I can't seem to get the delegate hookup to work. In CameraViewController.h I am getting that it Cannot find protocol definition for 'PhotoIngestionDelegate'.
Try this
#objc protocol PhotoIngestionDelegate {
}
I want to inherit my base class properties and methods which will be used by my several derived classes. I want these properties and methods to be exactly protected so that they will only be visible in derived class and not to any external class. But it always gives me some errors.
#interface BasePerson : NSObject
#end
#interface BasePerson ()
#property (nonatomic, strong) NSMutableArray<Person*>* savedPersons;
#property (nonatomic) BOOL shouldSavePerson;
#end
#interface DerivedPerson1 : BasePerson
#end
#implementation DerivedPerson1
- (instancetype)init
{
if (self = [super init]) {
self.savedPersons = [NSMutableArray array];
self.shouldSavePerson = NO;
}
return self;
}
It always gives me an error that
Property 'savedPersons' not found on object of type 'DerivedPerson1 *'
Property 'shouldSavePerson' not found on object of type 'DerivedPerson1 *'
How i can make use of inheritance in Objective C, I don't want savedPersons and shouldSavePerson properties to be visible to external classes. I only want them to visible in my base class and all the derived classes.
Any help will be great. Thanks
This is not something that the objectiveC really support. There are some ways though. So lets see.
If you put a property in the source file class extension then it is not exposed and you can not access it in the subclass either.
One way is to put all of the subclasses into the same source file as the base class. This is not a good solution at all as you do want to have separate files for separate classes.
It seems logical to import the BaseClass.m in the SubClass source file but that will produce a linker error saying that you have duplicate symbols.
And the solution:
Separate the extension into a separate header. So you have a MyClass
Header:
#import <Foundation/Foundation.h>
#interface MyClass : NSObject
#end
Source:
#import "MyClass.h"
#import "MyClassProtected.h"
#implementation MyClass
- (void)foo {
self.someProperty = #"Some text from base class";
}
#end
Then you create another header file (only the header) MyClassProtected.h which has the following:
#import "MyClass.h"
#interface MyClass ()
#property (nonatomic, strong) NSString *someProperty;
#end
And the subclass MyClassSubclass
Header:
#import "MyClass.h"
#interface MyClassSubclass : MyClass
#end
And the source:
#import "MyClassSubclass.h"
#import "MyClassProtected.h"
#implementation MyClassSubclass
- (void)foo {
self.someProperty = #"We can set it here as well";
}
#end
So now if the user MyClassSubclass he will not have the access to the protected property which is essentially what you want. But the downside is the user may still import MyClassProtected.h after which he will have the access to the property.
Objective-C doesn't have member access control for methods, but you can emulate it using header files.
BasePerson.h
#interface BasePerson : NSObject
#property (strong,nonatomic) SomeClass *somePublicProperty;
-(void) somePublicMethod;
#end
BasePerson-Private.h
#import "BasePerson.h"
#interface BasePerson ()
#property (nonatomic, strong) NSMutableArray<Person*>* savedPersons;
#property (nonatomic) BOOL shouldSavePerson;
#end
BasePerson.m
#import "BasePerson-Private.h"
...
DerivedPerson1.h
#import "BasePerson-Private.h"
#inteface DerivedPerson1 : BasePerson
...
#end
Now any class that #imports BasePerson.h will only see the public methods. As I said though, this is only emulating access control since if a class #imports *BasePerson-Private.h" they will see the private members; this is just how C/Objective-C is.
We can achieve using #protected access specifier
#interface BasePerson : NSObject {
#protected NSMutableArray *savedPersons;
#protected BOOL shouldSavePerson;
}
DerivedPerson1.m
#implementation DerivedPerson1
- (instancetype)init
{
if (self = [super init]) {
self->savedPersons = [NSMutableArray array];
self->shouldSavePerson = NO;
}
return self;
}
#end
OtherClass.m
#import "OtherClass.h"
#import "BasePerson.h"
#implementation OtherClass
- (void)awakeFromNib {
BasePerson *base = [[BasePerson alloc]init];
base->savedPersons = #[];//Getting Error. Because it is not a subclass.
}
#end
I'm trying to migrate some code from Objective-c to Swift, but i have problems at the beggining when i want to conform a Swift class with a Objective-c protocol and access this class from a objetive-c class. I'm doing something wrong, but i don't see it.
Objective-c protocol and obj-c class for testing (test_class.h)
#import <Foundation/Foundation.h>
#protocol test_delegate
-(void)returnData:(NSString*)data InMethod:(NSString*)method;
#end
#interface test_class : NSObject
#property (weak, nonatomic) id<test_delegate> delegate;
-(void)sendData:(NSString * )data;
#end
Objective-c implementation
#import "test_class.h"
#implementation test_class
-(id) init{
self = [super init];
if (self != nil){
self.delegate= nil;
}
return self;
}
-(id) initWithDelegate:(id<test_delegate>) delegate{
self = [super init];
if (self != nil){
self.delegate = delegate;
}
return self;
}
-(void)sendData:(NSString *)data{
[self.delegate returnData:data InMethod:#"method test"];
}
#end
Objetive-c brigde file
//
// Use this file to import your target's public headers that you would like to expose to Swift.
//
#import "test_class.h"
Swift file (FirstViewController.swift)
import UIKit
class FirstViewController: UIViewController, test_delegate {
var test : test_class!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
test = test_class()
test.delegate=self
test.sendData("show in log")
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func returnData(data: String!, inMethod method: String!) {
NSLog(data)
}
}
Finally the error compile gives me
2015-01-27 08:21:05.787 Test[4566:51164] -[Test.FirstViewController returnData:InMethod:]: unrecognized selector sent to instance 0x7fa6abd0aa20
2015-01-27 08:21:05.792 Test[4566:51164] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Test.FirstViewController returnData:InMethod:]: unrecognized selector sent to instance 0x7fa6abd0aa20'
This code, using only Obj-c classes works fine. What I'm doing wrong?
Using Xcode 6.1.1 and deployment target iOS 8.0
Thank you in advance.
UPDATE:
Swift has a weird behaviour when implement some method from a objective-c protocol: param's name must start with a tiny letter at the the begginig, else, compiler give you a compile-time error, and if not, give you a runtime error.
The unique solution I've found, is modify objective-c protocol method definition this way:
#protocol test_delegate
-(void)returnData:(NSString*)data InMethod:(NSString*)method;
#end
to:
#protocol test_delegate
-(void)returnData:(NSString*)data inMethod:(NSString*)method;
#end
Doing this change, it runs perfectly.
If anyone has an answer for this behaviour, is welcome to post and explain why this happens.
UPDATE 2:
Thank you to #Adam Freeman to point out another weird issue of Swift with classes names and variables names. Copied (with his permission) the code here:
Another thing to watch out for that is if your protocol delegate method takes its class as one of its parameters. Using this example:
#import <Foundation/Foundation.h>
#class TestClass;
#protocol TestDelegate
-(void)TestClass:(TestClass*)TestClass returnData:(NSString*)data inMethod:(NSString*)method;
#end
#interface TestClass : NSObject
#property (weak, nonatomic) id<TestDelegate> delegate;
-(void)sendData:(NSString * )data;
#end
This will cause problems with TestClass being found in your Swift code. The fix is:
#import <Foundation/Foundation.h>
#class TestClass;
#protocol TestDelegate
-(void)testClass:(TestClass*)testClass returnData:(NSString*)data inMethod:(NSString*)method;
#end
#interface TestClass : NSObject
#property (weak, nonatomic) id<TestDelegate> delegate;
-(void)sendData:(NSString * )data;
#end
Incidentally the Swift spec states that such things as classes and delegates should start with an upper case letter and methods and parameter names should start with a lower case letter.
Change:
func returnData(data: String!, inMethod method: String!) {
to
func returnData(data: String!, InMethod method: String!) {
and it should work. You use a capital letter in inMethod.
Another thing to watch out for that I ran into and this post helped me fix (thanX!) and that others may run into is if your protcol delegate method takes its class as one of its parameters. Such as ==>
#import <Foundation/Foundation.h>
#class TestClass;
#protocol TestDelegate
-(void)TestClass:(TestClass*)TestClass returnData:(NSString*)data inMethod:(NSString*)method;
#end
#interface TestClass : NSObject
#property (weak, nonatomic) id<TestDelegate> delegate;
-(void)sendData:(NSString * )data;
#end
This will cause problems with TestClass being found in your Swift code. The fix is:
#import <Foundation/Foundation.h>
#class TestClass;
#protocol TestDelegate
-(void)testClass:(TestClass*)testClass returnData:(NSString*)data inMethod:(NSString*)method;
#end
#interface TestClass : NSObject
#property (weak, nonatomic) id<TestDelegate> delegate;
-(void)sendData:(NSString * )data;
#end
Incidentally the Swift spec states that such things as classes and delegates should start with an upper case letter and methods and parameter names should start with a lower case letter. I know this is nit-picky but test_class really should be TestClass according to Apple's spec.
//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 want to use a custom method in a custom class in my viewcontroller
//Viewcontroller.h
#import "Class1.h"
//Class1.h
//#import "Class1+Category.h" // Deemed unnecessary in comments below.
#interface Class1: NSObject
-(void)doSomething;
#end
//Class1.m
#import "Class1.h"
#implementation Class1
-(void)doSomething{
NSLog("In doSomething");
}
#end
Now I want a category method of Class1.
//Class1+Category1.h
#import "Class1.h"
#interface Class1 (Category1) // ERROR : Cannot find interface declaration
-(void)doAnotherThing;
#end
//Class1+Category1.m
#import "Class1+Category.h"
#implementation Class1 (Category1)
-(void)doAnotherThing{
NSLog(#"Did Another thing");
}
#end
Finally - in my viewcontroller.m I see the doSomething method, but not the doAnother thing
//viewcontroller.m
Class1 *myClass1 = [[Class1 alloc]init];
[Class1 doSomething]; //Works great!
[Class1 doAnotherThing]; //Not recognized
I have added the -all_load to my target settings. I am out of ideas..do I use the #class? I get 'Cannot find interface declaration' error
Your class and category seems correct at first glance but your controller needs to import Class1+Category.h. Perhaps that's what you missed?