I want to create a new object, one of the property is (readonly).
Here is my code:
1/ My class (.h + .m)
#import <Foundation/Foundation.h>
#interface MyClass : NSObject
#property (readonly) NSString* myProperty;
#end
#import "MyClass.h"
#implementation MyClass
#end
2/ My class extension (.h)
#import "MyClass.h"
#interface MyClass ()
#property (readwrite) NSString* myProperty;
#end
3/ MyClassCategory (.h + .m)
#import "MyClass.h"
#interface MyClass (MyClassCategory)
+ (MyClass*) creatNewObject:(NSString*) mypro;
#end
#import "MyClass+MyClassCategory.h"
#import "MyClass_MyClassExtension.h"
#implementation MyClass (MyClassCategory)
+ (MyClass*) creatNewObject:(NSString*) mypro {
MyClass* newObject = [[MyClass alloc] init];
newObject.myProperty = mypro;
NSLog(#"New object have been created%#", newObject);
return newObject;
}
#end
#import <Foundation/Foundation.h>
#import "MyClass.h"
#import "MyClass+MyClassCategory.h"
int main(int argc, const char * argv[]) {
#autoreleasepool {
// insert code here...
NSLog(#"Hello, World!");
MyClass* newObject1 = [MyClass creatNewObject:(#"I am the new object!")];
NSLog(#"New object have been created%#", newObject1);
}
return 0;
}
after running the code in the main method, I got
2014-09-25 21:53:52.204 MyClass[2811:303] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MyClass setMyProperty:]: unrecognized selector sent to instance 0x100109e10'
014-09-25 22:36:05.746 MyClass[2989:303] -[MyClass setMyProperty:]: unrecognized selector sent to instance 0x100200130
I want to be enables edits to the properties of an existing class instance from category.
Can you help me please?
Thank you.
In MyClass.m, you also need to include the extension header.
#import "MyClass_MyClassExtension.h"
Otherwise the compiler won't see myProperty is redeclared as a read-write property while generating the implementation of MyClass.
Related
I wonder if it is possible to use #synthesize on a private #property so that the get/set methods have public access.
Right now my code looks something like this
SomeClass.h
#import <Foundation/Foundation.h>
#interface SomeClass : NSObject
{
#private
int somePrivateVariable;
}
#end
SomeClass.m
#import "SomeClass.h"
#interface SomeClass ()
#property int somePrivateVariable;
#end
#implementation
#synthesize somePrivateVariable;
#end
Then in some outside function I want to be able to write:
#import "SomeClass.h"
SomeClass *someClass = [[SomeClass alloc] init];
[someClass setSomePrivateVariable:1337]; // set the var
NSLog("value: %i", [someClass getSomePrivateVariable]); // get the var
I know that I can just create my own get/set methods in the header file but I would enjoy using the #synthesize very much more.
If you want a public property to mirror a private one, just override the public property's getter and setter and return the private one.
#interface Test : NSObject
#property NSObject *publicObject;
#end
Then, in the implementation:
#interface Test ()
#property NSObject *privateObject;
#end
#implementation Test
- (NSObject *)publicObject
{
return self.privateObject;
}
- (void)setPublicObject:(NSObject *)publicObject
{
self.privateObject = publicObject;
}
#end
I just started out programming in Objective C. This is very simple stuff but im wondering what im missing on my knowledge of properties, as far as I understand this should work but it gives me the error:
Property 'score' not found on object of type 'Player *'
I have a Player class and the code as follows below, each bolded is a separate file
Player.h has:
#import <Foundation/Foundation.h>
#interface Player : NSObject
#property int score;
#end
Player.m has:
#import "Player.h"
#implementation Player
- (id)init {
self = [super init];
if (self){
_score = 5000;
}
return self;
}
#end
main.m has
#import <Foundation/Foundation.h>
#import "Player.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
Player *firstPlayer = [[Player alloc] init];
NSLog(#"The default score is %i", [firstPlayer score]);
}
return 0;
}
Player.h is missing the following line which should go between the #import and #property lines:
#interface Player : NSObject
Where NSObject may be a different class, but needs to be whatever you intend to be subclassing.
I'm learning Objective-C.
I'm at the point of creating a simple class but when compiling, after the expected result, I get this errors.
2014-05-08 10:15:47.998 ClassCreation[978:903] This is a method call in the new object!
2014-05-08 10:15:48.007 ClassCreation[978:903] -[Employee setName:]: unrecognized selector sent to instance 0x10010c850
...
terminate called after throwing an instance of 'NSException'
(gdb)
Here it is the Employee.h
#import <Foundation/Foundation.h>
#interface Employee : NSObject
// properties
#property NSString *name;
#property NSDate *hireDate;
#property int employeeNumber;
-(void) someMethod;
#end
Here it is the Employee.m
#import "Employee.h"
#implementation Employee
// matching the method definition that is defined in the interface
-(void) someMethod {
NSLog(#"This is a method call in the new object!");
}
#end
Here it is the main.m
#import <Foundation/Foundation.h>
#import "Employee.h"
int main (int argc, const char * argv[])
{
#autoreleasepool {
// inside here, I instantiate a new object of my new employee class
Employee *fred = [[Employee alloc] init];
// call a method of our new object
[fred someMethod];
// change a property of new object
[fred setName:#"Fred Smith"];
}
return 0;
}
I'm on 10.6.8 with Xcode 4.2
With XCode 4.2 you need to add the line
#synthesize name,hireDate,employeeNumber;
to your Employee.m file after the #implementation line
Auto synthesis of properties only became available with XCode 4.4 - http://useyourloaf.com/blog/2012/08/01/property-synthesis-with-xcode-4-dot-4.html
You should look at upgrading your XCode version
I need to have property in class that is excluded from public framework headers, but it is available for use internally in other framework classes.
What I did right now is:
MyClass.h:
#interface MyClass: NSObject
#end
MyClass+Internal.h
#interface MyClass (Internal)
#property (nonatomic, copy) NSString *mySecretProperty;
#end
MyClass.m
#import "MyClass.h"
#import "MyClass+Internal.h"
#interface MyClass ()
#property (nonatomic, copy) NSString *mySecretProperty;
#end
#implementation MyClass
#end
And I can use private property like:
MyOtherClass.m:
#import "MyClass.h"
#import "MyClass+Internal.h"
#implementation MyOtherClass
- (void)test {
MyClass *myClass = [MyClass new];
NSLog(#"%#", myClass.mySecretProperty)
}
#end
But what I don't like about this setup is that I have duplicate declaration of property in my Internal Category and inside of anonymous Category.
Is there a way to improve this setup?
I think you could do with the class extension only, there is no need to use a category. The quick fix would be to remove the category name from the parenthesis, transforming it into the class extension, then remove the class extension declaration from the .m file.
After this you only import the extension header in your framework classes and you make sure it is a private header of your framework.
MyClass.h
#interface MyClass: NSObject
#end
MyClass+Internal.h
#import "MyClass.h"
#interface MyClass ()
#property (nonatomic, copy) NSString *mySecretProperty;
#end
MyClass.m
#import "MyClass.h"
#import "MyClass+Internal.h"
#implementation MyClass
#end
MyOtherClass.m:
#import "MyClass.h"
#import "MyClass+Internal.h"
#implementation MyOtherClass
- (void)test {
MyClass *myClass = [MyClass new];
NSLog(#"%#", myClass.mySecretProperty)
}
#end
The key is understanding the difference between categories and class extensions, see here: https://stackoverflow.com/a/4540582/703809
I am really new to Objective-C and when I was practicing the book exercises, I really am stuck here. Please help me solve this and I have been thinking what could cause this error for more than three hours. Still I didn't get it!
Best regards,
Raj.
Thanks in advance !
main.m
#import <Foundation/Foundation.h>
#import "XYZPerson.h"
#import "XYZShout.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
//XYZPerson *some = [[XYZPerson alloc]init];
XYZShout *some = [[XYZShout alloc]init];
[some sayHello];
// insert code here...
// NSLog(#"Hello, World!");
}
return 0;
}
XYZPerson.h
#import <Foundation/Foundation.h>
#interface XYZPerson : NSObject
#property NSString *firstName;
#property NSString *secondName;
#property NSDate *dob;
-(void) saySomething;
-(void) sayHello;
#end
XYZPerson.m
#import "XYZPerson.h"
#implementation XYZPerson
-(void) sayHello {
[self saySomething:#"Hello all"];
}
-(void) saySomething:(NSString *)greet {
NSLog(#"%#", greet);
}
#end
XYZShout.h
#import "XYZPerson.h"
#interface XYZShout : XYZPerson
// -(void) saySomething;
#end
XYZShout.m
#import "XYZShout.h"
#implementation XYZShout
-(void) saySomething:(NSString *)greet {
NSString *upperGreet = [greet uppercaseString];
[super saySomething:upperGreet]; // this is where I get the error mentioned above
}
#end
Got it working ! Thanks to #MatthewD , #trojanfoe , #JFS for your big help :)
It looks like you are testing inheritance so I will assume that XYZShout is supposed to be derived from XYZPerson. If so follow the suggestion from #JFS and make sure it does actually derive:
XYZShout.h:
#import <Foundation/Foundation.h>
#import "XYZPerson.h"
#interface XYZShout : XYZPerson
- (void)saySomething:(NSString *)greet;
#end
And also correct the definition of saySomething in XYZPerson (you missed off the parameter):
XYZPerson.h:
#import <Foundation/Foundation.h>
#interface XYZPerson : NSObject
#property NSString *firstName;
#property NSString *secondName;
#property NSDate *dob;
- (void)saySomething:(NSString *)greet;
// ^^^^^^^^^^^^^^^^^
- (void)sayHello;
#end
(Moved from comments into an answer...)
MatthewD: What happens if you change - (void) saySomething; in XYZPerson.h to - (void) saySomething:greet;?
Raj0689: Why does it run when I change it to saySomething:greet and not saySomething ? Since greet is defined only along with saySomething !!
When you call a method, the compiler needs to locate the signature of that method so it can verify that the method is being called correctly. The signature includes the method name and the number and types of parameters. The usual way of providing method signatures is by importing the header file that defines those signatures.
So, in XYZShout.m where you call:
[super saySomething:upperGreet];
The compiler searches XYZShout.h, which is imported by XYZShout.m, and XYZPerson.h, which is imported by XYZShout.h. In XYZShout.h, the following method was being found:
-(void) saySomething;
This matches the called method in name, but not in parameters, so the compiler does not consider this a match. No other definitions of saySomething are found anywhere, so it gives an error instead.
Please make sure to set the XYZShout.h interface to #interface XYZShout : XYZPerson?