I recently started learning Objective-C. I decided to make a class called "Student" with the properties age, name, and importantly, classes. I have put the classes in an NSArray full of NSStrings. My issue is, if I define it as an #property, it automatically creates a setter and getter method for it. I dont want that in my class. How do I define an NSArray as private data in the class, without allowing for the setter and getter?
Here's the header code:
#import <Foundation/Foundation.h>
#interface Student : NSObject
#property NSString * Name;
#property unsigned short age;
#property BOOL isFullTime;
#property NSMutableArray * Classes;
#end
[NSGreeter ThanksGuys];
You have a few popular options. Of course, you can substitute types as you wish:
A:
Place it in the header, and specify #private access.
// Student.h
#interface Student : NSObject
{
#private // << note: protected is the default when declared in this scope.
NSArray * ivar;
}
#end
B:
Place it in the #implementation block. you could specify access, but that is not usually an issue because it is not visible to any other translation.
// Student.m
#implementation Student
{
#private // << note: private is the default when declared in this scope.
NSArray * ivar;
}
#end
C:
Declare it in the class continuation:
// Student.m
#interface Student ()
{
NSArray * ivar;
}
#end
D:
Declare as a property in the class continuation:
// Student.m
#interface Student ()
#property (nonatomic, copy) NSArray * ivar;
#end
#interface Student : NSObject {
#private
NSMutableArray * Classes;
}
#property NSString * Name;
#property unsigned short age;
#property BOOL isFullTime;
#end
Use the keyword #private
#interface Student : NSObject
{
#private
NSMutableArray * Classes;
}
#property NSString * Name;
#property unsigned short age;
#property BOOL isFullTime;
#end
Related
I have the following class interface:
#interface MyClass : NSObject
#property int publicProperty;
#end
then the implementation:
#interface MyClass() // class extension
- (void)privateMethod; // private methods
#end
#implementation MyClass {
int _privateProperty;
}
#property int privateProperty = _privateProperty;
#end
this is what the Apple guy showed in WWDC, but is there any reason for NOT putting _privateProperty in class extension like:
#interface MyClass() // class extension
{
int _privateProperty;
}
- (void)privateMethod; // private methods
#end
Thanks!
I usually "force" private with an extension in the implementation
In your header
#interface MyClass : NSObject
{
}
#property (nonatomic, assign) int publicProperty;
#end
In your implementation file:
#interface MyClass ()
#property (nonatomic, assign) int privateProperty;
#end
#implementation MyClass
#synthesize privateProperty;
#synthesize publicProperty;
#end
You dont have to declare your ivars in both the interface and the implementation.Because you want to make them private you can just declared them in the implementation file like so:
#implementation {
int firstVariable;
int secondVariable;
...
}
//properties and code for your methods
If you wanted to, you can then create getter and setter methods so that you can access those variables.
The person you spoke to was right, though there is not any reason why you would NOT declare them the same way in the interface. Some books actually teach you that the #interface shows the public face of the class and what you have in the implementation will be private.
Do you mean you want to declare private instance variables?
You can do this:
#interface MyClass()
{
#private //makes the following ivar private
int _privateProperty;
}
With the "modern runtime" (64-bit MacOS post-10.5 and all versions of iOS), you don't need to declare instance variables at all.
// MyClass.h
#interface MyClass : NSObject
#property int publicProperty;
#end
// MyClass.m
#implementation MyClass
#synthesize publicProperty = _privateProperty; // int _privateProperty is automatically synthesized for you.
#end
I'm learning the objective C language and i ask a simple question,
when i do that :
// ParentClass.h
#interface ParentClass : NSObject
#property (read, strong) NSString *parentPublicStr;
#end
// ParentClass.m
#interface ParentClass ()
#property (readwrite, strong) NSString *parentPrivateStr;
#end
#implementation ParentClass
#synthesize parentPublicStr;
#synthesize parentPrivateStr;
#end
// Subclass SubClass.h
#interface SubClass : ParentClass
- (void) test;
#end
#implementation SubClass
- (void) test
{
// Its not possible to do that : [self setParentPrivateStr:#"myStrin"]
// And for parentPublicStr, it is public property so not protected, because i can change the value
// in main.c, and it's so bad..
}
#end
I would like create a property that is protected :x
Thx you. (Sorry for my english)
Objective-C does not provide for protected methods/properties. See this question.
Edit: Also see this answer. You can still practice encapsulation by declaring the property in a class extension and including the extension in subclasses.
You can manually create an ivar for the property as long as you use the same name prefixed with an underscore:
#interface ParentClass : NSObject
{
#protected
NSString* _parentPublicStr;
}
#property (read, strong) NSString *parentPublicStr;
#end
That makes the synthesized ivar for the property #protected (default is #private) and subclasses can then use the super class' ivar directly.
I have a hierarchy of model objects which I will be displaying on different type of UITableViewCell subclasses. All decision is made on the fly as to which model object should be used and corresponding UITableViewCell subclass' object is spawned and then set the model object to the UITableViewCell's subclass object so that it can fetch values from it.
My UITableViewCell hierarchy is something like this:
The base class Cell hierarchy:
#interface BaseCell : UITableViewCell
{
Base *baseObj_;
}
#end
The subclass of cell hierarchy:
#interface DerivedCell : BaseCell
{
}
#property (nonatomic, retain) Derived *derivedObject;
#end
#implementation DerivedCell
#synthesize derivedObject = baseObj_;
#end
The base class of Model object:
#interface Base : NSObject
{
NSString *title_;
}
#property (nonatomic, retain) NSString *title;
#end
The subclass of model hierarchy
#interface Derived : Base
{
NSString *detailedText_;
}
#property (nonatomic, retain) NSString *detailedText;
#end
When I do so, I am having errors in this line:
#synthesize derivedObject = baseObj_;
Which reads:
Property 'derivedObject' attempting to use ivar 'baseObj_' declared in super class BaseCell.
Type of property 'derivedObject' (Derived*) does not match type of ivar 'baseObj_' ('Base * __strong')
I want to use properties and synthesize them so that I can leverage the uses of properties (like using dot notation etc.). I have for now used accessors and setters which solves the problem:
#interface DerivedCell : BaseCell
{
}
-(Derived*)derivedObject;
-(void)setDerivedObject:(Derived*)newDerivedObject;
#end
But I was just wondering if I could somehow fix these errors to use the properties only.
Thanks,
Raj
Try the below code I have modified your code a bit as shown below
Since you can assign class Base object to class Derived in #synthesize, it can be achieved by this way, I know you have tried it already, I have tried it with the below code and able to access the variables with dot, try the below code and let me know if it is not working
#interface DerivedCell : BaseCell
{
Derived *derivedObject;
}
#property (nonatomic, retain) Derived *derivedObject;
#end
#implementation DerivedCell
#dynamic derivedObject;
- (void)setDerivedObject:(Base *)baseObj {
if (self.derivedObject == nil) {
derivedObject = [[Derived alloc] init];
}
derivedObject.detailedText = baseObj.title;
}
- (Derived *)derivedObject {
return derivedObject;
}
#interface Derived : Base
{
NSString *detailedText_;
}
#property (nonatomic, retain) NSString *detailedText;
#end
#implementation Derived
#synthesize detailedText = detailedText_;
#end
#interface BaseCell : UITableViewCell
{
Base *baseObj_;
}
#property (nonatomic, retain) Base *baseObj;
#end
#implementation BaseCell
#synthesize baseObj = baseObj_;
#end
#interface Base : NSObject
{
NSString *title_;
}
#property (nonatomic, retain) NSString *title;
#end
#implementation Base
#synthesize title = title_;
#end
Base *b = [[Base alloc] init];
b.title = #"Hello Raj";
BaseCell *bc = [[BaseCell alloc] init];
bc.baseObj = b;
DerivedCell *dc = [[DerivedCell alloc] init];
dc.derivedObject = b;
NSLog(#"Derive dc %#", dc.derivedObject.detailedText);
Another Solution which I have provided has an issue when I checked it
#interface BaseCell : UITableViewCell
{
NSString *baseTitle_;
}
#property (nonatomic, retain) NSString *baseTitle;
#end
#implementation BaseCell
#synthesize baseTitle = baseTitle_;
#end
#interface DerivedCell : BaseCell
{
NSString *derivedTitle_;
}
#property (nonatomic, retain) NSString *derivedTitle;
#implementation DerivedCell
#synthesize derivedTitle = baseTitle;
#end
When I created instance for the class and as shown below
DerivedCell *dCell = [[DerivedCell alloc] init];
dCell.baseTitle = #"Hello";
NSLog(#"%#",dCell.baseTitle);//Output was Hello
NSLog(#"%#",dCell.derivedTitle);//Output was (null)
It didn't assign the value to derivedTitle, If it is working for you please let me know
Another solution with memory referncing
#interface BaseCell : UITableViewCell
{
NSMutableString *baseTitle_;
}
#property (nonatomic, retain) NSMutableString *baseTitle;
#end
#implementation BaseCell
#synthesize baseTitle = baseTitle_;
#end
#interface DerivedCell : BaseCell
{
}
#property (nonatomic, retain) NSMutableString *derivedTitle;
#end
#implementation DerivedCell
#synthesize derivedTitle;
- (id) init
{
if ( self = [super init] )
{
baseTitle_ = [[NSMutableString alloc] init];
derivedTitle = baseTitle_;
}
return self;
}
#end
DerivedCell *dCell = [[DerivedCell alloc] init];
[dCell.baseTitle appendString:#"Hello"];
NSLog(#"baseTitle : %#",dCell.baseTitle);
NSLog(#"derivedTitle :%#",dCell.derivedTitle);
Console Output baseTitle : Hello derivedTitle :Hello
One pattern I've used for situations like this is to re-declare the property in a category on the derived class. The one structural change this approach requires from the code you posted is that it requires a same-named property (or equivalent getter/setter methods) to be defined in the base class. Consider the following snippet:
#interface BaseModel : NSObject
#end
#interface DerivedModel : BaseModel
#end
#interface BaseCell : UITableViewCell
{
BaseModel *baseObj_;
}
#property (nonatomic, retain) BaseModel *modelObject;
#end
#interface DerivedCell : BaseCell
#end
#interface DerivedCell (DowntypedPropertyCategory)
#property (nonatomic, retain) DerivedModel *modelObject;
#end
#implementation BaseModel
#end
#implementation DerivedModel
#end
#implementation BaseCell
#synthesize modelObject = baseObj_;
#end
#implementation DerivedCell
#end
In this pattern, the base class declares the iVar and the base-typed property, and synthesizes the implementation. The derived class declares the downcast-typed property in a category. Being in a category, the compiler won't force you to implement methods for that property. This gets you out of trying to synthesize against a superclass's iVar, instead relying on implementations that exist in the superclass, but declaring them to be of a different type. At runtime, the runtime will just end up calling the superclass methods (since Obj-C method dispatch is based on selector only, and does not have multiple dispatch.) As a result, clients of these properties can do stuff like this without any compile time warnings or errors:
#interface UnrelatedObject : NSObject
#end
#implementation UnrelatedObject
- (void)unrelatedMethod: (DerivedCell*)dc
{
DerivedModel* dm = dc.modelObject;
NSLog(#"dm: %#", dm);
}
#end
Again, the catch/minor difference is that in order for this to work, the base class must define a property of the same name (or equivalent getter/setter methods). That said, the property/methods in the base class could be declared (or in the case of methods, NOT even delayed) and defined in the base class's implementation file only, and thus would not be visible to other files merely including the header.
One other note: by using this approach you're missing out on compile time checks for things like mismatch between the property specifiers ([nonatomic|atomic], [readonly|readwrite], [assign|retain|copy]). I've found this pattern incredibly useful, but there are some potential pitfalls to keep an eye out for.
I hope I understand the question correctly, how about typing the model as id?
#interface BaseCell : UITableViewCell
#property(retain, nonatomic) id model;
#end
#implementation BaseCell
#synthesize model;
#end
Then the derived cells can use whatever model classes they want.
When you initialize an instance variable through synthesize, that variable is not accesible from any class that may inherit it.
It looks like you may have been trying to point synthesize to a public instance variable and I'm not sure if that is possible. It may be trying to declare a new variable with the same name which I'm sure would generate some compiler warnings at the least since that new declaration would hide an existing one and is less accessible.
You could simply write your own getter and setter to expose the instance variable.
- (Base *) baseObj {
return _baseObj;
}
- (void) setBaseObj:(Base *)val {
if( val != _baseObj ) {
[_baseObj release];
_baseObj = [val retain];
}
}
Hope this helps!
I'd like to use the #property syntax to declare a synthesized property that is publicly readonly but has a setter that can be called privately from within the class.
Since it's Objective-C, this basically means that the setFoo: method would be synthesized, but calling it outside of the class itself would result in a warning (unrecognized selector). To trigger the warning I have to declare the property readonly; is there any way to force a synthesized setter that is only available within the class?
I think what you're looking for are called class extensions. You would declare the property read-only in the header:
#interface MyClass : NSObject {
}
#property (readonly, assign) NSInteger myInteger;
#end
Then redeclare in your class extension in the implementation file:
#interface MyClass ()
#property (readwrite, assign) NSInteger myInteger;
#end
#implementation MyClass
#end
For more check out Apple's documentation
I might be late, but without extension i did using the following technique
#interface MyClass : NSObject {
NSString * name;
}
#property (readonly, strong) NSString * name;
#end
on the other hand in implementation file
#implementation MyClass
#synthesize name;
- (id)initWithItems:(NSDictionary *)items {
self = [super init];
if(self)
{
name = #"abc";
}
return self;
}
#end
doing so it will set your value and will be accessible as readonly.
Thanks.
So I have a class with a NSInteger in it and now I want to return the NSInteger value. For some kind of reason, the code for that is not working. I have already declared the #property for the NSInteger class.
#property (readwrite, assign, nonatomic) NSInteger numberFun;
- (NSInteger)sampleMethod {
...
return sample.numberFun;
}
The compiler says "Return from pointer without a cast". I'm pretty sure that means that I'm using a C type for an objective-c method. I want to know the work around for this. (Though I don't want it to return a casted NSInteger as a NSNumber).
Thanks
The following code sample compiles fine. I suggest you present a more complete example of your problem so we can figure out what you are doing wrong.
#interface MyObject : NSObject
{ }
#property (readwrite, assign, nonatomic) NSInteger numberFun;
#end
#implementation MyObject
#synthesize numberFun;
#end
#interface MyObject2 : NSObject
{ }
#property (nonatomic, copy) MyObject* sample;
#end
#implementation MyObject2
#synthesize sample;
- (NSInteger)sampleMethod { return sample.numberFun; }
#end