i was wondering how to access "static" vars from a model from different ViewControllers.
Should I go for:
static vars (if yes, how?)
static method
singleton + method
singleton + variable (custom getters)
#import "CategoryModel.h"
#implementation CategoryModel
-(NSArray*) allSelected {
return [[NSArray alloc] initWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:SELECTEDCATEGORIES_DEFAULTSKEY]];
}
-(NSString*) allSelectedAsUrlParams {
NSMutableString *categoryList = [NSMutableString string];
for (NSArray *category in self.allSelected) {
[categoryList appendString:[category valueForKey:#"value"]];
if(![[self.allSelected lastObject] isEqual:category]) {
[categoryList appendString:#","];
}
}
return categoryList;
}
#end
*Edit (working) *
// header
#import <Foundation/Foundation.h>
#interface CategoryModel : NSObject
+ (NSString*)allSelectedAsUrlParams;
#end
// implementation
#import "CategoryModel.h"
#implementation CategoryModel
+ (NSString*)allSelectedAsUrlParams {
return #"somethingGreat";
}
#end
// How to use
CategoryModel.allSelectedAsUrlParams
This is really going to be a matter of architectural preference, but if more than one class is going to need the static vars, this is one approach:
Constants.h
extern BOOL const TEST_MODE;
extern NSString * const SOME_STRING;
Constants.m
BOOL const TEST_MODE = YES;
NSString * const SOME_STRING = #"SomeString";
As an alternative, you can just add the extern NSString * const SOME_STRING; to the header of class that it is specific to (and the corresponding NSString * const SOME_STRING = #"SomeString"; in the .m) and then call that var directly by importing the header of the class with the constant you need and using SOME_STRING to get at it.
Related
macOS 11.5.2
Xcode 13.2.1
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <iostream>
int main(int argc, const char * argv[]) {
#autoreleasepool {
Class clazz = NSClassFromString(#"NSString");
uint32_t count = 0;
objc_property_t* properties = class_copyPropertyList(clazz, &count);
for (uint32_t i = 0; i < count; i++){
const char* name = property_getName(properties[i]);
std::cout << name << std::endl;
}
free(properties);
}
return 0;
}
I will take some snippets of the output：
hash
superclass
description
debugDescription
hash
superclass
description
debugDescription
vertexID
sha224
NS_isSourceOver
hash
superclass
description
debugDescription
...
From the output, we can find that properties such as hash, description, superclass, etc. will appear repeatedly several times, while some properties (such as UTF8String) do not appear in the result list.
How should I get the list of properties correctly?
I would appreciate it.
The reason you're not seeing UTF8String come up as a property is that it's not declared as a property in the main declaration of NSString, but rather in a category. On macOS 12.2.1/Xcode 13.2.1, the declaration of NSString boils down to this:
#interface NSString : NSObject <NSCopying, NSMutableCopying, NSSecureCoding>
#property (readonly) NSUInteger length;
- (unichar)characterAtIndex:(NSUInteger)index;
- (instancetype)init NS_DESIGNATED_INITIALIZER;
- (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
#end
All other properties and methods on NSString are declared in categories immediately afterwards:
#interface NSString (NSStringExtensionMethods)
#pragma mark *** Substrings ***
/* To avoid breaking up character sequences such as Emoji, you can do:
[str substringFromIndex:[str rangeOfComposedCharacterSequenceAtIndex:index].location]
[str substringToIndex:NSMaxRange([str rangeOfComposedCharacterSequenceAtIndex:index])]
[str substringWithRange:[str rangeOfComposedCharacterSequencesForRange:range]
*/
- (NSString *)substringFromIndex:(NSUInteger)from;
- (NSString *)substringToIndex:(NSUInteger)to;
// ...
#property (nullable, readonly) const char *UTF8String NS_RETURNS_INNER_POINTER; // Convenience to return null-terminated UTF8 representation
// ...
#end
When a property is declared in a category on a type like this, it doesn't get emitted as an actual Obj-C property because categories can only add methods to classes, and not instance variables. When a category declares a property on a type, it must be backed by a method and not a traditional property.
You can see this with a custom class, too — on my machine,
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#interface MyClass: NSObject
#property (nullable, readonly) const char *direct_UTF8String NS_RETURNS_INNER_POINTER;
#end
#interface MyClass (Extensions)
#property (nullable, readonly) const char *category_UTF8String NS_RETURNS_INNER_POINTER;
#end
#implementation MyClass
- (const char *)direct_UTF8String {
return "Hello, world!";
}
- (const char *)category_UTF8String {
return "Hi there!";
}
#end
int main(int argc, const char * argv[]) {
#autoreleasepool {
Class clazz = NSClassFromString(#"MyClass");
printf("%s properties:\n", class_getName(clazz));
uint32_t count = 0;
objc_property_t* properties = class_copyPropertyList(clazz, &count);
for (uint32_t i = 0; i < count; i++){
printf("%s\n", property_getName(properties[i]));
}
free(properties);
puts("-----------------------------------------------");
printf("%s methods:\n", class_getName(clazz));
Method *methods = class_copyMethodList(clazz, &count);
for (uint32_t i = 0; i < count; i++) {
SEL name = method_getName(methods[i]);
printf("%s\n", sel_getName(name));
}
free(methods);
}
return 0;
}
outputs
MyClass properties:
direct_UTF8String
-----------------------------------------------
MyClass methods:
direct_UTF8String
category_UTF8String
If you remove the actual implementations of the *UTF8String methods from the class, the property remains declared, but the category method disappears (because it doesn't actually have a synthesized implementation because of how categories work):
MyClass properties:
direct_UTF8String
-----------------------------------------------
MyClass methods:
direct_UTF8String
As for how to adjust to this: it depends on what purpose you're trying to fetch properties for, and why you might need UTF8String specifically.
NSString declares in its interface it implements methods, but it does not actually implement them, that is why when you print at runtime a list of the its methods it does not print what you expect.
The methods are implemented by other private classes, and when you initialize a new instance of NSString, instead of getting an instance of NSString you get an instance of that private class that have the actual implementation.
You can see that by printing the class type of a string, the following prints NSCFString or NSTaggedPointerString, not NSString:
NSString* aString = [NSString stringWithFormat: #"something"];
NSLog(#"%#", [aString class]);
And this prints __NSCFConstantString:
NSLog(#"%#", [#"a constant string" class]);
This pattern is called a class cluster pattern.
If you modify to dump the methods of the NSCFString you will get a "redactedDescription", it seems you are prevented to query these classes.
Suppose that I have a class that holds a mutable array. I want to make sure that if other classes ask for the array they will get a non-mutable type, but in the owning class, it is actually an instance of NSMutableArray, so that I can add and remove items.
#import "Person.h"
#class Asset;
#interface Employee : Person
{
NSMutableArray *_assets;
}
#property (nonatomic,copy) NSArray *assets;
-(void)addAssets:(Asset *)a;
The question is, do I have to modify the accessor methods into something like this, or will it automatically behave like I want?
#import "Employee.h"
#import "Asset.h"
#implementation Employee
/* Accessors for assets properties
-(NSArray *)assets
{
return [_assets copy];
}
-(void)setAssets:(NSArray *)assets
{
_assets = [assets mutableCopy ];
}
*/
-(void)addAssets:(Asset *)a
{
//is assets nil?
if (!_assets) {
//Create Array
_assets = [[NSMutableArray alloc]init];
}
[_assets addObject:a];
}
ppalancica's answer is incorrect. The copy attribute means only that the setter will take a copy when the property is set. The synthesized getter will not return a copy. You must implement that behavior yourself:
- (NSArray *)assets
{
return [_assets copy];
}
You might want to make an internal-only accessor that doesn't make a copy. You could also redeclare the property privately; client code will then be contracted to treat the array it requests as immutable.
This code demonstrates that the synthesized getter returns the uncopied object:
#import <Foundation/Foundation.h>
#interface ArrayReturner : NSObject
#property (copy, nonatomic) NSArray * array;
#end
#implementation ArrayReturner
{
NSMutableArray * _array;
}
- (BOOL)myArrayIsIdenticalTo:(NSArray *)otherArray
{
return _array == otherArray;
}
#end
int main(int argc, const char *argv[])
{
#autoreleasepool {
ArrayReturner * a = [ArrayReturner new];
[a setArray:#[#1, #2]];
NSArray * returnedArray = [a array];
// Does not throw
NSCAssert([a myArrayIsIdenticalTo:returnedArray],
#"Returned array is a separate instance.");
}
return 0;
}
Because you already specified the attribute "copy" for the array property, there is no need to override the getter and setter. The compiler will do all the heavy work for you.
If you specify "strong" instead, the getter and setter would look like:
-(NSArray *)assets
{
return _assets;
}
-(void)setAssets:(NSArray *)assets
{
_assets = assets;
}
And that may be a problem.
There is actually a WWDC conference that explains all these details. For NSString properties it is more recommended to use copy, and you can see it a lot like that in the iOS SDK frameworks.
I'm steadily getting the hang of Objective-C, but am still very much a beginner and have a beginner-level question hopefully someone could shed some light on:
If I have a very simple project and want to set a constant that I'll use throughout—say, a NSDictionary with keys being month names and values being days in that month—how is this done? (I.e., what command form and where to put it?)
NOTE: If this example is already possible using built-in functions, perhaps we could just pretend it isn't for the purposes of this question ;)
The answer depends on the type of your constant. If all you need is an int or a double, you can use preprocessor and the #define CONST 123 syntax. For Objective C classes, however, you need to do a lot more work.
Specifically, you would need to hide the constant behind a class method or a free-standing function. You will also need to add a prototype of that method or function in the header file, provide a function-scoped static variable to store the constant, and add code to initialize it.
Here is an example using a simple NSDictionary:
Header: MyConstants.h
#interface MyConstants
+(NSDictionary*)getConstDictionary;
#end
Implementation: MyConstants.m
+(NSDictionary*)getConstDictionary {
static NSDictionary *inst = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
inst = #{
#"key1": #"value1",
#"key2": #"value2",
#"key3": #"value3"
};
});
return inst;
}
Usage:
NSString *val = [[MyConstants getConstDictionary] objectForKey:#"key2"];
The accepted answer is correct, but if you prefer operate with variable (not trough method). I can suggest this pattern:
#implementation MyClass
static NSSet *mySetOfObjects;
+ (void)initialize {
mySetOfObjects = [[NSSet alloc] initWithObjects:#"one", #"two", #"three", nil];
}
// Example usage:
+ (BOOL)isRecognizedString:(NSString *)searchItem {
return [mySetOfObjects containsObject:searchItem];
}
#end
As for me - it looks better.
For more details the source is here.
Let's assume you want to declare an NSString constant in your class that holds a url. In your header .h file you will need the following:
#import
extern NSString * const BaseURL;
#interface ClassName : NSObject {
You will then need to set it's value in your main .m file as follows:
#import "ClassName.h"
NSString * const BaseURL = #"http://some.url.com/path/";
#implementation ClassName
You can now access this constant throughout your class or subclasses. Here's an example of usage:
NSString *urlString = [NSString stringWithFormat:#"%#%#", BaseURL, #"filename.html"];
If your constants are strings then you can use this form:
MyObject.h:
extern NSString *const kJanuary;
....
extern NSString *const kDecember;
#interface MyObject : NSObject
{
...
}
#end
MyObject.m:
NSString *const kJanuary = #"January";
....
NSString *const kDecember = #"December";
#implementation MyObject
....
#end
You can then use the constant kJanuary, for example, from anywhere when using your class.
I'm only starting with Objective-C and it's still hard for me to do some pretty basic things. Here's what I want to achieve - I need to create a class that would hold all static data of my application which I guess could be represented with a number of NSString ** arrays, such as this one:
NSString *animalNames[NUM_ANIMALS] = {#"fox", #"wolf", #"elephant", #"giraffe"};
I want to be able to access these arrays in a static way from anywhere in my application. Something like this:
StaticData.animalNames[1]
How would I accomplish this in terms of #property, #interface, #synthesize and all this stuff?
I need to create a class that would hold all static data of my application
Here's an example of what you are talking about. It's a basic singleton class with a static array of your animals.
#import <Foundation/Foundation.h>
#interface Foo:NSObject
+ (id)sharedFoo;
- (NSArray *)animals;
#end
#implementation Foo
static NSArray *animals;
+ (void)initialize {
animals = [NSArray arrayWithObjects:#"fox",#"wolf",#"giraffe",#"liger",nil];
}
+ (id)sharedFoo {
static dispatch_once_t pred;
static Foo *cSharedInstance = nil;
dispatch_once(&pred, ^{ cSharedInstance = [[Foo alloc] init]; });
return cSharedInstance;
}
- (NSArray *)animals {
return animals;
}
#end
int main(int argc, char *argv[]) {
NSLog(#"Animals = %#",[[Foo sharedFoo] animals]);
}
This application logs the following to the console:
2012-10-08 10:01:46.814 Untitled[77085:707] Animals = (
fox,
wolf,
giraffe,
liger )
EDIT:
If you favor the dot syntax/property notation, you could just implement the following in the class interface:
#property (readonly) NSArray *animals;
which would let you write:
[Foo sharedFoo].animals
etc.
I have the following class in my iOS application (it is like an abstract class from the Java world).
#implementation WSObject
static NSDictionary* _dictionary = nil;
+(NSDictionary*) dictionary {
if (_dictionary == nil) {
_dictionary = [NSKeyedUnarchiver unarchiveObjectWithFile:[self localStorePath]];
}
return _dictionary;
}
...
#end
I then have multiple classes which implement this above WSObject with the class method dictionary. The problem is, that each of these classes should have their own _dictionary, but they are all sharing the same object from the super class. I could, of course, copy to all the subclasses, but that would break the reusability. Besides this getter, there are other class methods in WSObject which mutate the dictionary. Because of this, there would be a several class methods which should be in every subclass.
How can I solve this in a smart way? Please tell me if my description is insufficient.
Associative references seem like they'll do the trick. You can essentially tack some storage on to the class object itself. (I'm using NSStrings here, in place of the dictionaries you want to use, just for demonstration.)
Superclass:
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#interface Stuper : NSObject
// Accessor method for the "class variable"
+ (NSString *) str;
// Analog to your +localStorePath
+ (NSString *) quote;
#end
#import "Stuper.h"
// The doc suggests simply using the address of a static variable as the key.
// This works fine, even though every class is (as in your problem) using
// the same key, because we are associating to a different class each time.
static char key;
#implementation Stuper
+ (NSString *) str {
NSString * s = objc_getAssociatedObject(self, &key);
if( !s ){
s = [self quote];
// You'll probably want to use OBJC_ASSOCIATION_RETAIN for your dictionary.
// self inside a class method is the class object; use that as
// the associator. The string is now tied to the associator, i.e.,
// has the same lifetime.
objc_setAssociatedObject(self, &key, s, OBJC_ASSOCIATION_COPY);
}
return s;
}
+ (NSString *) quote {
return #"It was the best of times, it was the worst of times.";
}
#end
Subclass:
#import "Stuper.h"
#interface Stub : Stuper #end
#import "Stub.h"
#implementation Stub
+ (NSString *) quote {
return #"Call me Ishmael.";
}
#end
Trying this out:
#import <Foundation/Foundation.h>
#import "Stuper.h"
#import "Stub.h"
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSLog(#"%#", [Stuper str]);
NSLog(#"%#", [Stub str]);
[pool drain];
return 0;
}
Each class object now has its own string, associated with it.
2011-12-05 23:11:09.031 SubClassVariables[36254:903] It was the best of times, it was the worst of times.
2011-12-05 23:11:09.034 SubClassVariables[36254:903] Call me Ishmael.
The only downside here is that you'll have to call the accessor method every time you want the object; you don't have a pointer you can use directly. You can call objc_getAssociatedObject in the superclass as an accessor, too, of course, since it has access to key.
In order to give each subclass its own dictionary, store a second dictionary object in your primary dictionary using the class name as the key. For example:
static NSMutableDictionary *_dictionary = nil;
+ (NSDictionary*)dictionary
{
if (_dictionary == nil)
_dictionary = [[NSKeyedUnarchiver unarchiveObjectWithFile:[self localStorePath]] mutableCopy];
NSString *key = NSStringFromClass( [self class] );
if ( [_dictionary objectForKey:key] == nil )
[_dictionary setObject:[NSMutableDictionary dictionary] forKey:key];
return [_dictionary objectForKey:key];
}
Perhaps you can return a copy of the dictionary
#implementation WSObject
static NSDictionary* _dictionary = nil;
+(NSDictionary*) dictionary {
if (_dictionary == nil) {
_dictionary = [NSKeyedUnarchiver unarchiveObjectWithFile:[self localStorePath]];
}
return [_dictionary copy];
}
...
#end
Keep in mind that if you modify _dictionary you will get a copy of that modified dictionary which may differ from what is on disk.
How often is this being called? is it really necessary to cache the file contents in this static _dictionary object?
Why not just fetch it every time form disk, assuming it isn't too often that performance comes into question.
#implementation WSObject
+(NSDictionary*) dictionary {
return [NSKeyedUnarchiver unarchiveObjectWithFile:[self localStorePath]];
}
...
#end