I want to make a singleton containing information "title, comments, Two picture" and it saves all the information in an array
I want to do is these objects in my application I use it All The Time
#interface CarteManager : NSObject {
NSMutableArray *carteMan ;
}
#property(nonatomic,retain) NSMutableArray *carteMan;
+(CarteManager*)sharedInstance;
-(void)ajouttitre:(NSString*)txt;
-(void)ajoutcom:(NSString*)com;
-(void)ajoutimage1:(UIImage*)img;
-(void)ajoutimage2:(UIImage*)img;
#end
In order to create a Singleton you will need a static instance.
#implementation CarteManager
static CarteManager *_carteManager = nil;
+(CarteManager*)sharedInstance {
if (!_carteManager) {
_carteManager = [[CarteManager alloc] init];
}
return _carteManager;
}
// your other codes
#end
And before creating a Singleton, make sure that you really need a Singleton. Please pay special attention to Singleton: How should it be used.
You didn't state your problem. If it's how to make the object a singleton, you can find several possible implementations in the question What does your Objective-C singleton look like?.
Related
I have a small function which I want to rewrite, so that function is valid for every class.
At the moment I have 10 of the same functions which all work same but every function is for another class.
I know, that I have to do it with reflections, but I am not so sure how to do it.
I already read this link:
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html
The functions I am talking about are:
-(NSCountedSet *)MissionGetReferecedNested:(id)modelObject
{
setOfObjects = [[NSCountedSet alloc]initWithArray:modelObject.MissionSectionList];
return setOfObjects;
}
-(NSCountedSet *)MissionGetSectionReferecedNested:(id)modelObject
{
setOfObjects = [[NSCountedSet alloc]initWithArray:modelObject.DamageAccountList];
return setOfObjects;
}
MissionSectionList and DamageAccountList are both NSMutableArrays from two different classes.
Is it possible to see if a class consists a NSMutableArray and if yes then it should call the .... modelObject.MyMutableArray?
You can use reflection like this:
- (NSCountedSet *)MissionGet:(id)modelObject
{
SEL propertySelector = NULL;
if ([modelObject respondsToSelector:#selector(MissionSectionList)]) {
propertySelector = #selector(MissionSectionList);
} else if ([modelObject respondsToSelector:#selector(DamageAccountList)]) {
propertySelector = #selector(DamageAccountList);
}
if (!propertySelector) {
[NSException raise:#"Invalid modelObject value" format:#"Model object %# does not contain any recognised selectors", modelObject];
}
return [[NSCountedSet alloc] initWithArray:[modelObject performSelector:propertySelector]];
}
But a more common technique among cocoa programmers would be:
- (NSCountedSet *)MissionGet:(id <MyCustomProtocol>)modelObject
{
return [[NSCountedSet alloc] initWithArray:[modelObject missionArray]];
}
Where you would accept any object which confirms to the protocol MyCustomProtocol. The protocol is defined in a header files somewhere, using:
#protocol MyCustomProtocol
#property (readonly) NSArray *missionArray;
#end
And then in each of your classes, declare it as implementing the protocol:
#interface MissionSectionListClass <MyCustomProtocol>
And add a method implementation:
#implementation MissionSectionListClass <MyCustomProtocol>
- (NSArray *)missionArray
{
return self.MissionSectionList;
}
#end
Using protocols is a bit more code, but it's the "right" way to go. It allows you to add support for new classes, without any change to your MissiongGet... method.
More info about protocols: http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProtocols.html
EDIT : Cleared all my answer to this :
I think it's not possible to check if a class has a member variable of specified type. You can only check if a class has a specified method.
So, in this case it will be best if you make all your NSMutableArray list the same name, and then create a declared property for this list, and then do a respondsToSelector in your ...GetReferencedNested method.
So, for example, in all of your class create this property :
#property (nonatomic, retain) NSMutableArray * list;
and then in the ..MissionGetReferencedNested method :
if ([modelObject respondsToSelector:#selector(list)])
...
Correct me if i'm wrong...
In terms of style I'd also follow Abhi's suggestion.
But if you really want to inspect a class that you are stuck with and, for example build a NSCountedSet with the first NSMutableArray variable you can find, you could do it like this:
#import "Utilities.h"
#import <Foundation/Foundation.h>
#import <objc/objc-runtime.h>
#implementation Utilities
+ (NSCountedSet*)initCountedSetWithFirstArrayinObject:(id)someObject {
unsigned int c;
Ivar *ivar_arr = class_copyIvarList([someObject class], &c);
for (unsigned int i = 0; i < c; i++) {
if ([#"#\"NSMutableArray\"" isEqualToString:
[NSString stringWithCString:ivar_getTypeEncoding(ivar_arr[i]) encoding:NSUTF8StringEncoding]
]) {
return [[NSCountedSet alloc] initWithArray:object_getIvar(someObject, ivar_arr[i])];
}
}
return nil;
}
#end
Of course this has very limited real world use because it depends on you knowing that the first array will be the one you're interested in.
I think I have to go with the runtime type editing.(http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html)
The idea with the protocols was good but there I have to change a lot of things in the classes.(which is not possible/allowed) for me. My intension was only to change the functions so that I have only one function for all classes.
I think with the runtime type editing I can check what classes and attributes I have (?) Am I right?
Did somebody already work with runtime type editing?
From documentation, the MKMapView property, Annotations, is a NSArray and not a NSMutableArray. So Annotations is supposed to be "immutable". But MKMapView's instant methods : addAnnotation and removeAnnotation are capable of changing the Annotations array. So on the surface there seems to be some inconsistencies. There must be something I have missed. Hope that somebody knowledgable could shed some light on this.
By declaring the annotations property an NSArray, code that accesses the array through that property cannot safely modify it and must treat it as an immutable NSArray. However, that doesn't mean that the array itself is immutable.
Here's an example of how something like this might work:
#interface MyObject
{
// instance variables
NSMutableArray* internalArrayRepresentation;
}
// properties
#property (nonatomic, readonly) NSArray* immutableAccessor;
// methods
-(void)addItem:(NSObject*)object;
#end
#implementation MyObject
#synthesize immutableAccessor=internalArrayRepresentation;
-(id)init
{
if ((self = [super init]))
{
// create the mutable array
internalArrayRepresentation = [[NSMutableArray alloc] init]
}
}
-(void)addItem:(NSObject*)object
{
[internalArrayRepresentation addObject:object];
}
...
#end
In this example, you can see that internalArrayRepresentation is a mutable array, and that its accessible outside of MyObject as immutableAccessor. But because the property definition says that immutableAccessor is an NSArray, callers need to treat it that way and can't manipulate it.
There are other implementations that can accomplish this as well.
The typical reason to use a pattern like this is because you want MyObject to maintain control over the contents of the array: maybe only certain objects can be added, maybe objects need to be modified or cloned on the way in, maybe anything can be added but nothing can be removed, etc.
You're meant to use addAnnotation and removeAnnotation to add/remove annotations instead of manipulating the annotations array directly.
I assume both those functions do some processing as well as adding/removing annotations from the array.
Here is a simple one for you guys . I'm defining a class to store variables in so I can reuse those variables in different ViewControllers .
Here is how I do it, it`s obviously not working ( that's why I'm asking a question ... ):
I declare a class :
VariableStore.h
#interface VariableStore : NSObject {
int evTe;
}
#property (nonatomic) int evTe;
+ (VariableStore *)shareInstance;
#end
VariableStore.m
#implementation VariableStore
#synthesize evTe;
+ (VariableStore *)sharedInstance {
static VariableStore *myInstance = nil;
return myInstance;
}
#end
Now in my FirstViewController I want to set the value for evTe :
[[VariableStore sharedInstance] setEvte:2];
NSLog(#"value testing, %i", evTe);
And this keeps on returning 0 unfortunately, Im obviously missing something important here but I can't figure out what it is .
Later on Id like to set the value for evTe here in the FirstViewController and then reuse it back in the SecondViewController ..
You are setting your shared instance to nil and then returning it:
static VariableStore *myInstance = nil;
return myInstance;
A nil instance won't hold your variable. It's nil.
First off you shouldn't be using a singleton to pass around variables. If you're going to do that then you might as well just use global variables instead (don't do that either by, the way). Second, if you insist on using a singleton, you need to read up on how to use them.
Finally, if you want to pass variables between view controllers, you either need another view controller that is a parent to the two to facilitate passing data between them, or one needs to call the other and take the first one or its data as a parameter.
Well, you're asking for the value of evTe without calling the object to which it belongs. Try this:
NSLog(#"value testing, %i", [[VariableStore sharedInstance] evTe]);
If you keep using the singleton for a number of times, you might want to do:
VariableStore *vStore = [VariableStore sharedInstance];
so you can do:
[vStore setEvTe:2];
NSLog(#"value testing, %i", [vStore evTe]);
And look out for what Matt said about nilling your singleton ;)
I think in nslog you should output not just evTe, but [[VariableStore sharedInstance] evTe].
First, you have to declare the static variable outside the function, in a way both controllers can access.
static VariableStore* myInstance = nil;
The singleton sharedInstance should be:
if(myInstance == nil)
{
myInstance = [[VariableStore] alloc] init];
}
return myInstance;
Hey all. I know this sounds simple, but I can't find a way to do it. I have a method in Obj-C that takes in a NSString and then should create a new class with the String as its title.
-(DataModel *)createDataModel:(NSString *)dataModel_name {
DataModel *[initWithString:dataModel_name] = [[DataModel alloc] init];
}
I know I have some problems in this. For starters, I don't know how to define a return on an object whose name could change. Second, I know this doesn't compile considering the initWithString method is wrong. I just don't know what to do or what method to use so that I can create this DataModel object with the specified name...
If your title is setup correctly, as a property:
-(DataModel *)createDataModel:(NSString *)dataModel_name {
DataModel *model = [[DataModel alloc] init];
model.title = dataModel_name;
return model;
}
That would require in your datamodel.h:
#interface DataModel {
NSString *title;
}
#property (nonatomic, retain) NSString *title;
#end
And in your .m:
#implementation DataModel
#synthesize title;
#end
But your question isn't clear if your real purpose is trying to instantiate different classes based on the dataModel_name or if you just have a single generic class with a title that should be set to dataModel_name.
Depending on what you want to do, there are different answers. If you really want different classes based on the name, then you should do things differently. You can use the Cocoa specific type: id, to return any object from a method. Then the method, NSClassFromString() to create the object:
- (id)createDataModel:(NSString *)dataModel_name {
id model = [[NSClassFromString(dataModel_name) alloc] init];
[model setTitle:dataModel_name];
return model;
}
Or you can define a Protocol (Interface in java parlance) that declares the features of your data model. Your method would return that instead.
NSClassFromString() will do what you want. Also, initially declaring variables as type id allows you to set their explicit type later on. So:
id dataModel = [[NSClassFromString(dataModel_name) alloc] init];
To locate or create a new class:
Class arbitraryClass = NSClassFromString(dataModel_name);
if ( nil == arbitraryClass ) arbitraryClass = objc_allocateClassPair( [DataModel class] , [dataModel_name UTF8String] , 0 );
To create a new instance of an object with your newly created class:
DataModel *modelWithArbitratyClassName = [[arbitraryClass alloc] init];
Creating new classes at runtime is not usually a good idea.
So, it seems you want to dynamically add an Instance variable to an object at runtime. You don't get this for free. CALayer and CAAnimation can do something similar to this, you can read about it here
You could add similar functionality to your own objects using Key-value-coding, and more specifically the method valueForUndefinedKey. There will be some KVC specific caveats so you should really make sure you are familiar with and understand KVC. Take a look at this, it might be just want you want.
A dictionary is used to store the value and key, and to retrieve the value when you try to access it.
I have a class that contains a few instance methods which need to be called from another class. I know how to do that -
TimeFormatter *myTimeFormatter = [[TimeFormatter alloc] init];
[myTimeFormatter formatTime:time];
However, I don't want to have to alloc and init TimeFormatter every time I need to call one of its methods. (I need to call TimeFormatter's methods from various methods in another class).
I tried putting
TimeFormatter *myTimeFormatter = [[TimeFormatter alloc] init];
"by itself", or not in any blocks, but when I compile, I get an "initializer element is not constant" error.
Any input is greatly appreciated!
You can use the singleton pattern. You can read more about it here.
Specifically, you'd do something like:
static TimeFormatter* gSharedTimeFormatter = nil;
#implementation TimeFormatter
+ (TimeFormatter*)sharedTimeFormatter {
if (!gSharedTimeFormatter) {
#synchronized(self) {
if (!gSharedTimeFormatter) {
gSharedTimeFormatter = [[TimeFormatter alloc] init];
}
}
}
return gSharedTimeFormatter;
}
...
#end
Notice that we check if the variable is null, and if it is, we take a lock, and check again. This way, we incur the locking cost only on the allocation path, which happens only once in the program. This pattern is known as double-checked locking.
However, I don't want to have to alloc and init TimeFormatter every time I need to call one of its methods. (I need to call TimeFormatter's methods from various methods in another class).
I think it's worth clarifying some OOP terminology here.
The reason you need to alloc and init TimeFormatter is because your methods are instance methods. Because they're instance methods, you need an instance, and that's what alloc and init provide. Then you call your methods on (send messages to) the instance ([myTimeFormatter formatTimeString:…]).
The advantage of allowing instances is that you can keep state and settings in each instance, in instance variables, and make the latter into publicly-visible properties. Then you can deliberately have multiple instances, each having its own settings configured by whatever's using that instance.
If you don't need that functionality, you don't need to make these instance methods. You can make them class methods or even C functions, and then you don't need a TimeFormatter instance. With class methods, you send messages directly to the class ([TimeFormatter formatTimeString:…]).
And if you do want settings shared among all instances (and you don't have any state to keep), then you're right that you can just have one instance—a singleton.
The reason for that parenthesis is that shared state is bad, especially if two threads may use the time formatter concurrently. (For that matter, you could say that about settings, too. What if one thread wants seconds and the other doesn't? What if one wants 24-hour and the other wants 12-hour?) Better to have each thread use its own time formatter, so that they don't get tripped up by each other's state.
(BTW, if TimeFormatter is the actual name of your class: You are aware of NSDateFormatter, right? It does let you only format/parse the time.)
Here's a detail example of a sharedMethod. Credit goes here
#implementation SearchData
#synthesize searchDict;
#synthesize searchArray;
- (id)init {
if (self = [super init]) {
NSString *path = [[NSBundle mainBundle] bundlePath];
NSString *finalPath = [path stringByAppendingPathComponent:#"searches.plist"];
searchDict = [[NSDictionary alloc] initWithContentsOfFile:finalPath];
searchArray = [[searchDict allKeys] retain];
}
return self;
}
- (void)dealloc {
[searchDict release];
[searchArray release];
[super dealloc];
}
static SearchData *sharedSingleton = NULL;
+ (SearchData *)sharedSearchData {
#synchronized(self) {
if (sharedSingleton == NULL)
sharedSingleton = [[self alloc] init];
}
return(sharedSingleton);
}
#end
A very nice, and easy, way to setup a Singleton is to use Matt Gallager's SYNTHESIZE_SINGLETON_FOR_CLASS.
It sounds like you want to make TimeFormatter a singleton, where only one instance can be created. Objective-C doesn't make this super easy, but basically you can expose a static method that returns a pointer to TimeFormatter. This pointer will be allocated and initialized the first time in, and every time after that same pointer can be used. This question has some examples of creating a singleton in Objective-C.
You are trying to declare your variable outside the class? If to do it the way you want to do it you gotta declare it as static so
static TimeFormatter *myFormatter=...
From the name of the class though i dont see why you would wnat to keep one instance of your class... you can also do this with a singleton as described above, that is if you want to keep one instance of your class for the app as a whole.