When I declare a property in objective-C, I also add the synthesize clause to get accessors
#interface StoreManager ()
#property (nonatomic, copy) NSString *writeStoresTimer;
#implementation StoreManager
#synthesize writeStoresTimer
I usually use the following syntax to set value to a property
[self setWriteStoresManager:#"Data"];
Is the above statement same as self.writeStoresTimer = #"Data" ? Will this also call the set-accessor
Is the above statement same as self.writeStoresTimer = #"Data"?
Yes, it is exactly the same.
Indeed, if you want to override the default setter method that is automatically synthesized, you define:
- (void)setWriteStoresTimer:(NSString *)string;
and then your custom implementation will be called through the dot-syntax.
From Apple reference:
You can think of a property declaration as being equivalent to declaring two accessor methods. Thus
#property float value;
is equivalent to:
- (float)value;
- (void)setValue:(float)newValue;
Yes. They both do the same thing.
From Apple's Documentation:
Objective-C provides a dot (.) operator that offers an alternative to
square bracket notation ([]) to invoke accessor methods. Dot syntax
uses the same pattern that accessing C structure elements uses:
You can see the full documentation in The Objective C Programming Language
Yes self. and set uses accessors
only time you dont is when your within the same class and just use the pointers name
Related
I have class A, which exposes a way of getting and setting an object of type Foo. In property parlance, I generally declare this in the interface:
#property (nonatomic, strong) Foo * foo;
This (in modern ObjC) generates both the accessors and an ivar, _foo for storage.
If I want to do custom work in the accessors, I can implement one or both of them myself. But what if I not only want to do custom work, I actually don't want the ivar? In other words, I'm doing something else with the Foo object, like handing it back and forth to another internal object that I'm composed with. I don't actually need to keep storage for foo in the instance of A at all.
It seems like I have two choices:
Declare the property, implement both accessors, and simply ignore the fact that the compiler creates storage for _foo, and never use it.
Declare my accessors explicitly: - (Foo *)foo and - (void)setFoo:(Foo *)foo in the interface, like I used to in pre-modern ObjC.
The first seems inelegant at runtime, and the second seems inelegant in the declaration (where I'd probably now have a mix of properties and property-like accessors).
Is there a way to declare a property and have it serve as purely a declaration?
Use the #dynamic keyword in the implementation file. The usual discussion of #dynamic describes it as not creating the accessors at compile time. Not usually mentioned is that is also has the effect of doing nothing to create storage for the property, which is exactly what is desirable in this case.
#implementation A
#dynamic foo;
- (Foo *)foo
{
// get a Foo from somewhere and return it.
}
- (void)setFoo:(Foo *)foo
{
// do something with foo
}
#end
(Note: answered my own question since I discovered this while writing up the question and it seemed interesting and nonobvious.)
If you override both the setter and getter and don't use the variable within the setter and getter, a variable will not be created.
For example, if you have a class for which you want a firstName and lastName property, but perhaps also a setter and getter for a fullName property, if your fullName setter simply parses a string into firstName and lastName and sets these properties to that (and never stores the full string into a fullName variable), and your fullName getter simply returns the concatenated firstName + lastName and never uses a fullName variable, one will never be created.
This is according to Apple's official documentation. Scroll down to "You Can Implement Custom Accessor Methods"
#dynamic is probably the way to go.
However, there are two other ways you can do this as well:
An Unimplemented Category
You can use an un-implemented category to declare a property, but not get the backing storage:
#interface Foo : NSObject
#end
#interface Foo (UnimplementedProperties)
#property (strong) id bar;
#end
#implementation Foo
#end
By not declaring the implementation of the category (#implementation Foo (UnimplementedProperties)), the properties won't be synthesized.
A Protocol
You can declare the properties on a protocol, and then make your class conform to that protocol. This has the same effect as the unimplemented category: the methods are declared, but the properties are not synthesized.
#protocol FooProperties <NSObject>
#property (strong) id bar;
#end
#interface Foo : NSObject <FooProperties>
#end
I have this property:
#property (nonatomic, getter = getSolutionsCount, setter = setSolutionsCount:) NSInteger solutionsCount;
and implementation
- (NSInteger)getSolutionsCount {
return self.solutionsCount;
}
and I get EXC_BAD_ACCESS on this method - (NSInteger)getSolutionsCount.
What am I doing wrong here?
dot syntax is basically a shortcut for calling the getter. You have infinite recursion in your getter method.
What you need to do is return the instance variable directly:
- (NSInteger)getSolutionsCount {
//latest xcode makes variables with _property name automatically
return _solutionsCount;
//older versions of xcode or having written #synthesize solutionsCount
//will necessitate
//return solutionsCount;
}
Also just FYI objective-c convention is to have the getter method be defined as just the variable name. A getter which is the same as the property name is assumed if you don't write a getter in the property declaration
EDIT:
also i'm assuming this isnt the whole implementation for your getter because if it is let the compiler make it for you automatically, you don't need to write anything. (or by writing #synthesize propertyName = _propertyName in your implementation block with older versions of xCode)
The line self.solutionsCount is translated to [self getSolutionCount]. You are making a recursive call.
If you simply want to return the synthesized ivar then don't even implement this method. But if you do then simply call return _solutionCount;.
The problem is that self.solutionsCount is identical to [self getSolutionsCount], so your getter is directly recursive. You probably want to access the underlying ivar directly, to do so use self->_solutionsCount. Or, if you prefer not to explicitly use self, simply _solutionsCount.
There are several problems here:
According to the naming convention getters should not start with get. To read the value you need to use self.solutionsCount. Hence, you do not need to specify the name of the getter method in the property declaration.
You do not need to specify the name of the setter for it will be automatically generated.
The property should look like this:
#property (nonatomic, assign) NSInteger solutionsCount;
You do not need to write a custom getter implementation to make it work. Ask the compiler to synthesize the methods for you:
#synthesize solutionsCount;
If you want to have a direct access to the instance variable, ask compiler to sythesize it for you:
#synthesize solutionsCount = _solutionsCount;
Read objective-c and naming convention docs first. They will help enormously.
Good luck!
I'm currently using the iOS 5 SDK trying to develop my app.
I'm trying to make an NSString a property, and then to synthesize it in the .m file (I have done this before with no issues). Now, I came across this: "Semantic Issue: Property's synthesized getter follows Cocoa naming convention for returning 'owned' objects."
This is my code:
.h
#interface ViewController : UIViewController {
NSString *newTitle;
}
#property (strong, nonatomic) NSString *newTitle;
.m
#synthesize newTitle;
Does anyone have a clue how I could fix this?
Thanks!!
My guess is that the compiler version you’re using follows the memory management rules for declared properties, too — more specifically, for declared properties’ accessors:
You take ownership of an object if you create it using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy”.
A property named newTitle, when synthesised, yields a method called -newTitle, hence the warning/error. -newTitle is supposed to be a getter method for the newTitle property, however naming conventions state that a method whose name begins with new returns an object that’s owned by the caller, which is not the case of getter methods.
You can solve this by:
Renaming that property:
#property (strong, nonatomic) NSString *theNewTitle;
Keeping the property name and specifying a getter name that doesn’t begin with one of the special method name prefixes:
#property (strong, nonatomic, getter=theNewTitle) NSString *newTitle;
Keeping both the property name and the getter name, and telling the compiler that, even though the getter name starts with new, it belongs to the none method family as opposed to the new method family:
#ifndef __has_attribute
#define __has_attribute(x) 0 // Compatibility with non-clang compilers
#endif
#if __has_attribute(objc_method_family)
#define BV_OBJC_METHOD_FAMILY_NONE __attribute__((objc_method_family(none)))
#else
#define BV_OBJC_METHOD_FAMILY_NONE
#endif
#interface ViewController : UIViewController
#property (strong, nonatomic) NSString *newTitle;
- (NSString *)newTitle BV_OBJC_METHOD_FAMILY_NONE;
#end
Note that even though this solution allows you to keep newTitle as both the property name and the getter name, having a method called -newTitle that doesn’t return an object owned by the caller can be confusing for other people reading your code.
For the record, Apple have published Transitioning to ARC Release Notes, in which they state:
You cannot give a property a name that begins with new or copy.
They’ve already been notified that their statement is not quite accurate: the culprit is the getter method name, not the property name.
Edit 17 Jan 2015: I’ve just noticed a recent commit to Clang that suggests option 3 above (using objc_method_family(none)), including a fix-it, for the general case where a property name matches one of the special method family prefixes. Xcode will likely incorporate this change eventually.
Unacceptable Object Names
newButton
copyLabel
allocTitle
Acceptable Object Names
neueButton
mCopyLabel
_allocTitle
#arc #auto-synthesized #xcode-4.6.1
** EDIT **
Apparently you can't use mutableCopy either.
The name of the member starting with new is what triggers the warning. Change the name to editedTitle and the warning will go away. I was unable to find documentation confirming this but through testing was able to determine that member variables that begin with 'new' aggravate the compiler.
ARC does not allow to use "New...." in property name. but you can use "newTitle" by changing getter name.
#property (nonatomic, strong, getter=theNewTitle) NSString *newTitle;
It doesn't look like what Bavarious was suggesting was what you wanted to do. All you want to do is declare an instance variable NewTitle and then synthesize the property. We used to have to declare the instance variable and property. No more.
Now, I believe the right way of doing this is the following:
.h
#interface ViewController : UIViewController
#property (nonatomic, strong) NSString *newTitle;
.m
#synthesize newTitle = _newTitle; // Use instance variable _newTitle for storage
The instance variable for the property newTitle is synthesized. You don't want your instance variable to be the same as your property - too easy to make mistakes.
See Example: Declaring Properties and Synthesizing Accessors
In CoreData if you use "new..." in attribute (compile normally) it will crash randomly with a "bad access" exception.
There is no crash log and the line shown with the "All Exceptions Breakpoint" will not help you at all.
Writing a setter manually with the name same as the property's removed this warning.
NS_RETURNS_NOT_RETAINED is used to solve the naming problem.
#property (nonatomic, copy) NSString *newTitle NS_RETURNS_NOT_RETAINED;
We can find its definition as follows:
#define NS_RETURNS_NOT_RETAINED __attribute__((ns_returns_not_retained))
The 'ns_returns_not_retained' attribute is the complement of 'ns_returns_retained'. Where a function or method may appear to obey the Cocoa conventions and return a retained Cocoa object, this attribute can be used to indicate that the object reference returned should not be considered as an "owning" reference being returned to the caller. The Foundation framework defines a macro NS_RETURNS_NOT_RETAINED that is functionally equivalent to the one shown below.
Besides the issue that you should/can't use "new" in front of you property names, let say one more thing: Try to avoid "new" in front of names in general. "New" is dependent on time. Currently it is new for you, but some time later you maybe want to implement something new again. So using "new" in names is always bad. Try to think this way: In the programming world, "new" is always creating something: a new instance of something.
In your case when you want to assign a different title then the current name your property titleReplacement.
One more thing: Try to name functions and methods with the verb first, like setSomething or getSomething.
But in properties try to name the object first, like heightMinimum, heightMaximum, etc. -> when you use your inspector when you are coding, you always looking for objects. Try it out. ;-)
try this:-
#property (nonatomic,retain) NSString *newTitle;
How to declare an array of characters so that all the functions that has been defined inside the class can use it with the updated values.
Getting errors when defining the char data[4096] in the #synthesize definition.
#interface A: NSObject
{
char data[4096];
}
#property(nonatomic,retain)char data;
#end
#implementation A
#synthesize data
#end
I am getting "No declaration of the property 'pData' found in the interface"
Not sure why you get that error, but several things are clearly wrong in your code:
data instance variable and property for it have different types. Property declaration should be
#property(nonatomic) char[4096] data;
You must use retain attribute only for obj-c types properties, for plain c-types use assign (or don't specify anything as assign is used by default)
Exposing your pointer to char directly to changes may be not a good idea - better make your property readonly and make special method to change its contents:
#property(nonatomic, readonly) char[4096] data;
- (void) changeData:...//some parameters here
P.S. May be consider using NSString* (or NSMutableString*) instead of char[]?
P.P.S. Or if you just store some random byte data consider using NSData/NSMutableData for that. (Thanks #bbum for suggesting that)
I take for example the UIButton interface.
Here the first rows of #private definition :
#private
CFMutableDictionaryRef _contentLookup;
UIEdgeInsets _contentEdgeInsets;
UIEdgeInsets _titleEdgeInsets;
And here 2 of these ivar, that are defined as properties:
#property(nonatomic) UIEdgeInsets contentEdgeInsets;
#property(nonatomic) UIEdgeInsetstitleEdgeInsets;
However these 2 properties are not defined on the ivars i found in private method (which have suffix _).
I'm not sure to understand how could be implemented setter and getter for these 2 properties to refer to the private ivars.
And a second question... i used to create properties for ivar, thus, if i have an ivar FOO i can create a #property for FOO. Is it a normal behavior create property for a non existing ivar ? (in this case contentEdgeInsets is not an attribute for this class... on the contrary _contentEdgeInset is defined in #interface and this's a valid ivar). Ok what i missed with this argument ?
When you #synthesize these properties you do so like
#synthesize contentEdgeInsets = _contentEdgeInsets;
^property name ^iVar name
Check out the Property Implementation Directives section in the documentation.
By default, a property will use the ivar whose name is the same as that of the property, but it's also possible to specify an ivar of a different name. Do this in your #synthesize statement in the class implementation.
In the modern runtime, used pretty much everywhere at this point, you don't actually have to declare the ivar at all -- if you synthesize accessors for a property and there's no matching ivar, the runtime will provide one.
Finally, properties with #dynamic rather than #synthesized accessors don't necessarily need an ivar at all -- you're providing the accessors in this case, so you're free to derive the value of the property however you like.