guys.
How can I access the variable which I made by #property instruction?
I learned that prefix _ makes possible to access when I use my own getter/setter in an objective-c course.
//Person.h
#import <Foundation/Foundation.h>
#interface Person : NSObject
#property NSInteger age;
// getter
- (NSInteger)age;
// setter
- (void)setAge:(NSInteger)age;
#end
// Person.m
#import "Person.h"
#implementation Person
// getter
- (NSInteger)age {
return _age;
}
// setter
- (void)setAge:(NSInteger)age {
_age = age;
}
#end
But that code gave me errors Use of undeclared identifier '_age'.
How can I fix that?
Thanks!
You should add explicit synthesize for ivar, as below
#implementation Person
#synthesize age=_age;
I understand how to subclass PFObject, but I am not certain how to perform additional custom code in an accessor, while still calling the generic implementation of that accessor as defined and #dynamic-ally added by Parse (which does the proper thing depending on the property's type, e.g. PFRelation, and so forth).
For instance...
// MyPFObjectSubclass.h
#import <Parse/Parse.h>
#interface MyPFObjectSubclass.h : PFObject<PFSubclassing>
#property (retain, nonatomic) id myProperty;
+ (NSString *)parseClassName;
#end
// MyPFObjectSubclass.m
#import "MyPFObjectSubclass.h"
#import <Parse/PFObject+Subclass.h>
#implementation MyPFObjectSubclass
#dynamic myProperty;
+ (NSString *)parseClassName {
return #"MyPFObjectSubclass";
}
- (void)setMyProperty:(id)someProperty {
// insert some custom code here, e.g. for validation...
// call the generic, dynamic implementation of setMyProperty, but how?
// obviously, you cannot call [super setMyProperty:someProperty];
}
#end
Any help is appreciated.
All you need to do is implement your own accessors and skip #dynamic
I'm new to ObjectiveC and Xcode and I'm having a strange behavior:
This is the Packet class header: Packet.h
#import <Foundation/Foundation.h>
#interface Packet : NSObject
{
short index;
NSData *packetData;
short totalChunks;
}
#property (nonatomic) short index;
#property (strong, nonatomic) NSData *packetData;
#property (nonatomic) short totalChunks;
#end
And this is Packet.m
#import "Packet.h"
#implementation Packet
#synthesize index;
#synthesize packetData;
#synthesize totalChunks;
-(id)init
{
self = [super init];
return self;
}
#end
The problem is i can't use getter and setter although it seems to me that properties are declared and synthesized correctly!
for example:
#import "TransferManager.h"
#implementation TransferManager
-(void)sendAckPacket
{
Packet *packet = [[Packet alloc] init];
packet.index; //ERROR HERE: Property not found on object of type Packet *
}
#end
I know there is no TransferManager.h attached becaues I don't want to write useless stuff, but it imports "Packet.h". Otherwise i should have error during the initialization of *packet.
I'm stuck... Any Help? :)
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.
I came across a library written in Objective C (I only have the header file and the .a binary).
In the header file, it is like this:
#interface MyClass : MySuperClass
{
//nothing here
}
#property (nonatomic, retain) MyObject anObject;
- (void)someMethod;
How can I achieve the same thing? If I try to declare a property without its corresponding ivar inside the interface's {}, the compiler will give me an error. Ultimately, I want to hide the internal structure of my class inside the .a, and just expose the necessary methods to the header file. How do I declare instance variables inside the .m? Categories don't allow me to add ivar, just methods.
For 64 bit applications and iPhone applications (though not in the simulator), property synthesis is also capable of synthesizing the storage for an instance variable.
I.e. this works:
#interface MyClass : MySuperClass
{
//nothing here
}
#property (nonatomic, retain) MyObject *anObject;
#end
#implementation MyClass
#synthesize anObject;
#end
If you compile for 32 bit Mac OS X or the iPhone Simulator, the compiler will give an error.
You may use of the same idiom used in Cocoa classes. If you have a look to NSString class interface in NSString.h you'll see that there is no instance variable declared. Going deeper in GNUstep source code you'll find the trick.
Consider the following code.
MyClass.h
#interface MyClass : NSObject
// Your methods here
- (void) doSomething;
#end
MyClass.m
#interface MyClassImpl : MyClass {
// Your private and hidden instance variables here
}
#end
#implementation MyClass
+ (id) allocWithZone:(NSZone *)zone
{
return NSAllocateObject([MyClassImpl class], 0, zone);
}
// Your methods here
- (void) doSomething {
// This method is considered as pure virtual and cannot be invoked
[self doesNotRecognizeSelector: _cmd];
}
#end
#implementation MyClassImpl
// Your methods here
- (void) doSomething {
// A real implementation of doSomething
}
#end
As you can see, the trick consist in overloading allocWithZone: in your class. This code is invoked by default alloc provided by NSObject, so you don't have to worry about which allocating method should be used (both are valid). In such allocWithZone:, you may use the Foundation function NSAllocateObject() to allocate memory and initialize isa for a MyClassImpl object instead of MyClass. After that, the user is dealing with a MyClassImpl object transparently.
Of course, the real implementation of your class shall be provided by MyClassImpl. The methods for MyClass shall be implemented in a way that considers a message receiving as an error.
You can use a class extension. A class extension is similar as category but without any name. On the Apple documentation they just define private methods but in fact you can also declare your internal variables.
MyClass.h
#class PublicClass;
// Public interface
#interface MyClass : NSObject
#property (nonatomic, retain) PublicClass *publicVar;
#property (nonatomic, retain) PublicClass *publicVarDiffInternal;
- (void)publicMethod;
#end
MyClass.m
#import "PublicClass.h"
#import "InternalClass.h"
// Private interface
#interface MyClass ( /* class extension */ )
{
#private
// Internal variable only used internally
NSInteger defaultSize;
// Internal variable only used internally as private property
InternalClass *internalVar;
#private
// Internal variable exposed as public property
PublicClass *publicVar;
// Internal variable exposed as public property with an other name
PublicClass *myFooVar;
}
#property (nonatomic, retain) InternalClass *internalVar;
- (void)privateMethod;
#end
// Full implementation of MyClass
#implementation MyClass
#synthesize internalVar;
#synthesize publicVar;
#synthesize publicVarDiffInternal = myFooVar
- (void)privateMethod
{
}
- (void)publicMethod
{
}
- (id)init
{
if ((self = [super init]))
{
defaultSize = 512;
self.internalVar = nil;
self.publicVar = nil;
self.publicVarDiffInternal = nil; // initialize myFooVar
}
return self;
}
#end
You can give MyClass.h to anyone with just your public API and public properties. On MyClass.m you declare your member variable private and public, and your private methods, on your class extension.
Like this it's easy to expose public interfaces and hide detail implementation. I used on my project without any troubles.
According to the documentation I've been looking at there is no problem. All you have to do to hide instance variables is to declare them at the start of the #implementation section, inside { ... }. However, I'm a relative newcomer to Objective C and there's a chance I have misunderstood something - I suspect that the language has changed. I have actually tried this system, using XCode 4.2, building code for the iPad, and it seems to work fine.
One of my sources for this idea is the Apple developer documentation at http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/objectivec/Chapters/ocDefiningClasses.html, which gives this pattern:
#implementation ClassName
{
// Instance variable declarations.
}
// Method definitions.
#end
Two possibilities:
It could be taking advantage of the modern runtime's ability to synthesize instance variables, as bbum suggested.
The property might not have an underlying instance variable in that class. Properties do not necessarily have a one-to-one mapping with instance variables.
No you can't. But you can do this if you're not using #property:
.h
#interface X : Y {
struct X_Impl* impl;
}
-(int)getValue;
#end
.m
struct X_Impl {
int value;
};
...
#implementation X
-(void)getValue {
return impl->value * impl->value;
}
#end
How about a macro trick?
Have tested code below
have tested with dylibs - worked fine
have tested subclassing - Warning! will break, I agree this makes the trick not that useful, but still I think it tells some about how ObjC works...
MyClass.h
#interface MyClass : NSObject {
#ifdef MYCLASS_CONTENT
MYCLASS_CONTENT // Nothing revealed here
#endif
}
#property (nonatomic, retain) NSString *name;
#property (nonatomic, assign) int extra;
- (id)initWithString:(NSString*)str;
#end
MyClass.m
// Define the required Class content here before the #import "MyClass.h"
#define MYCLASS_CONTENT \
NSString *_name; \
int _extra; \
int _hiddenThing;
#import "MyClass.h"
#implementation MyClass
#synthesize name=_name;
#synthesize extra=_extra;
- (id)initWithString:(NSString*)str
{
self = [super init];
if (self) {
self.name = str;
self.extra = 17;
_hiddenThing = 19;
}
return self;
}
- (void)dealloc
{
[_name release];
[super dealloc];
}
#end
DON'T do this, but I feel it should be noted that the runtime has the ability to add ivars whenever you want with class_addIvar
I was able to do the following in my library:
myLib.h:
#interface MyClass : SomeSuperClass <SomeProtocol> {
// Nothing in here
}
- (void)someMethods;
#end
myLib.m
#interface MyClass ()
SomeClass *someVars;
#property (nonatomic, retain) SomeClass *someVars;
#end
#implementation MyClass
#synthesize someVar;
- (void)someMethods {
}
#end
The protocol is optional of course. I believe this also makes all your instance variables private though I'm not 100% certain. For me it's just an interface to my static library so it doesn't really matter.
Anyway, I hope this helps you out. To anyone else reading this, do let me know if this is bad in general or has any unforeseen consequences. I'm pretty new to Obj-C myself so I could always use the advice of the experienced.
I don't think the following code written in another answer is working as expected.
The "SomeClass *someVars" defined in the extension class is not an instance variable of MyClass. I think it is a C global variable. If you synthesize someVars, you will get compile error. And self.someVars won't work either.
myLib.h
#interface MyClass : SomeSuperClass <SomeProtocol> {
// Nothing in here
}
- (void)someMethods;
#end
myLib.m
#interface MyClass ()
SomeClass *someVars;
#property (nonatomic, retain) SomeClass *someVars;
#end
#implementation MyClass
#synthesize someVar;
- (void)someMethods {
}
#end