I am very much new to objective-c and I'm struggling with this problem for a while! Here is my class prototype:
#interface YoCatchModel : NSObject
/**
Name of the Yo user. Currently this is local
*/
#property (nonatomic, strong) NSString* username;
/**
History of the messages sent with Yo
*/
#property (nonatomic, strong, readonly) NSMutableArray* historyArray;
/*
implement init method
*/
+ (instancetype) initmethod;
I should allocate memory for my history mutable array in this method which is read only.
I want to make another init method that takes a username string parameter. This new initWithUsername method should call init within its definition.
And here is implementation which I am trying to implement an init method using instancetype as the return type. But I am not really sure how to
Allocate memory for the array.
Call another init method for the user name.
#implementation YoCatchModel
+ (instancetype)initmethod {
return [[[self class] alloc] init];
}
I appreciate if anyone can give me some hint how to do this. So far I have read these pages to get to here:
http://www.techotopia.com/index.php/An_Overview_of_Objective-C_Object_Oriented_Programming#Declaring.2C_Initializing_and_Releasing_a_Class_Instance
https://developer.apple.com/library/ios/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/DefiningClasses/DefiningClasses.html#//apple_ref/doc/uid/TP40011210-CH3-SW7
https://developer.apple.com/library/ios/releasenotes/ObjectiveC/ModernizationObjC/AdoptingModernObjective-C/AdoptingModernObjective-C.html#//apple_ref/doc/uid/TP40014150-CH1-SW11
The initWithUsername method becomes the designated initializer of your class and would look something like:
- (instancetype)initWithUsername:(NSString *)username
{
self = [super init];
if (self) {
_username = [username copy];
_historyArray = [NSMutableArray new];
}
return self;
}
You should make the default init method use the designated initializer:
- (instancetype)init
{
return [self initWithUsername:nil];
}
and note that this code works on the property backing instance variables, which start with _, rather than using self. (which won't work with a readonly property anyway), and this is to avoid possible KVO side-effects of the property setter methods.
Related
I'm trying to learn about delegation in Objective-C, and am having a minor issue with a variable losing it's data in the transfer process. I have Class1 that contains an NSMutableArray. The array gets populated, then I would like to transfer the array's values to Class2, and display it. Here is the relevant code in Class1:
//Class1.h
#class Class1;
// define the protocol for the delegate
#protocol Class1Delegate
#required
-(void)sayHello:(Class1 *)customClass withAntArray:(NSMutableArray *)antArray;
#end
#interface Class1 : MySuperClassName
#property (nonatomic, assign) id delegate;
-(void)helloDelegate;
#end
//Class1.m:
#interface Class1 ()
#property (nonatomic, strong) NSMutableArray *antOccurenceTimes;
#end
#implementation Class1
#synthesize antOccurenceTimes;
-(void)helloDelegate
{
// send the message to the delegate
[_delegate sayHello:self withAntArray:self.antOccurenceTimes];
}
Now, this is what I have in Class2:
#import "Class1.h"
#interface Class2 : UIView <Class1Delegate>
#end
// Class2.m:
- (void)appropriateTimeToCallMethod {
Class1 *initAntMarks = [[Class1 alloc] init];
initAntMarks.delegate = self;
[initAntMarks helloDelegate];
}
-(void)sayHello:(Class1 *)customClass withAntArray:(NSMutableArray *)antArray {
NSLog(#"Hello! %#", antArray.description);
}
The antArray.description reads as "NULL". Now, I figured that obviously it will be null, because I just created an entirely new instance of the class right before calling upon the needed method. I feel like I may have something mixed up, and being so new to delegation, I'm not sure exactly what. Does anyone know what I need to tweak to utilize Delegation?
I forgot to add that I did initialize it in Class1, and it gets populated just fine. It's only in class2 that this is occurring.
I initalize antOccuranceTimes in a separate method in ClassA in the snippet below, and the NSLog fires twice...
NSLog(#"Array initalized in class A");
antOccurenceTimes = [NSMutableArray new];
Change this line:
#property (nonatomic, assign) id delegate;
to:
#property (nonatomic, weak) id <Class1Delegate> delegate;
assign should only be used for C primitives, not Objective-c object references. You should also be checking if your object actually conforms to the delegate before messaging the delegate.
Edit:
I think you may be confused about the purpose of delegation.
Class1 *initAntMarks = [[Class1 alloc] init];
initAntMarks.delegate = self;
[initAntMarks helloDelegate];
Why are you calling a method on an object which in turn calls a delegate method when you could simply create a method that returns the NSMutableArray? The way you have your code currently set up requires that before the call to -helloDelegate you have to have filled the array with the appropriate objects. The purpose of delegation in MVC is to inform an object about an event that took place inside of another object. You are "delegating" the task off to another object, or you could say, that another object if responsible for the fulfillment of the task. Read the Apple Docs on Delegation. Delegation in your code is not the correct pattern to implement, as I stated you can simply return that array with a method call.
Edit 2:
There are two ways you can achieve this, through property methods or through an explicit method that returns your array. If you choose to use property methods, the property declaration must be in the public interface i.e. the .h file so that your class can all the accessors when the object is being implemented.
//Inside the .h
#property (nonatomic, strong) NSMutableArray *antOccurenceTimes;
This will automatically provide you with two accessor methods for the antOccurenceTimes property. These are the getter -antOccurenceTimes and setter -setAntOccurenceTimes: methods. Now after you initialize the class and fill your array you can call -antOccurenceTimes to return the array.
You can also create an explicit method that return the array:
- (NSMutableArray *)hello{
//Do something here
return _antOccurenceTimes;
}
You have not yet initialized the antOccurenceTimes. Of cause it is nil. There are many options depending on what you need. You can, for example, initialize it in a init function:
- (instancetype)init {
self = [super init];
if( self ) {
antOccurenceTimes = [NSMutableArray array];
[antOccurenceTimes addObject:#"Hello World"];
}
}
Or maybe initialize it before you call the delegate the function.
-(void)helloDelegate
{
// send the message to the delegate
self.antOccurenceTimes = [NSMutableArray array];
[self.antOccurenceTimes addObject:#"Hello World"];
[_delegate sayHello:self withAntArray:self.antOccurenceTimes];
}
I think you get my point.
Very simple question. Is it possible to create a class which is a list by it self? I mean:
I do
taskList *taskList1 = [[taskList alloc] init];
And than simply:
taskList1 addObject:[task1]
May seem stupid, but I'm totally new to O-C syntax
I'd need two methods:
-(instancetype) init;
which just initialize as an empty list
+(instancetype)taskList;
to allocate taskList instance
and last thing:
In interface i use:
#interface taskList : NSObject
or
#interface taskList : NSMuttableArray
I got stuck on something specific, didn't I? I'm sorry that I bother you with my programming level.
Alright, I gave up, just last question, because I have to finish it very soon.
I changed my approach I added
#property NSMutableArray *list;
Why does this:
taskList *TL1 =[taskList initTaskList];
task *task1 = [[task alloc] init];
task *task2 = [[task alloc] init];
TL1.list addObject:[task1];
doesn't work, I have "Expected identifier" Error
If you read the subclassing notes on NSArray / NSMutableArray you'll see that Apple recommend against subclassing them because they are a class cluster. (i.e. what you really get when you ask for one is an undocumented subclass, and the initialiser decides which undocumented subclass to return to you based on some undocumented qualifiers..
So just make an NSObject subclass which owns a (private) strong property of type NSMutableArray, and publish an api to access that array..
eg
#import "modelList.h"
//dont worry header is empty, its up to you to do that.. this is a subclass on NSObject
#interface modelList()
#property (strong, nonatomic) NSMutableArray *backingArray;
#end
#implementation modelList
#synthesize backingArray = _backingArray;
-(instancetype )init{
if (self = [super init]) {
[self setBackingArray:[[NSMutableArray alloc]init]];
}
return self;
}
//public API (the stuff that is prototyped in the header..)
-(id)objectAtIndex:(NSUInteger )index{
return [self.backingArray objectAtIndex:index];
}
-(BOOL )containsObject:(id)object{
return [self.backingArray containsObject:object];
}
-(void )addObject:(id)object{
//example application, qualifying object..
if ([object conformsToProtocol:#protocol(NSCoding)]) {
[self.backingArray addObject:object];
}
}
-(NSUInteger )count{
return [self.backingArray count];
}
//etc etc declare publicly the things you need to get the job done
#end
so far this is just a face for a mutable array obviously, but it gives you a place for whatever other model logic you need. good luck
I want to do something like this:
#property (nonatomic, retain) NSObject *obj1;
#property (nonatomic, retain) NSObject *obj2;
- (id)init {
if ((self = [super init])) {
[SomeClass someFuncWithParam1:*(self.obj1) param2:*(self.obj2)];
}
}
#implementation SomeClass
+ (void)someFuncWithParam1:(NSObject **)param1 param2:(NSObject **)param2 {
//init obj1;
...
//init obj2;
...
}
#end
I haven't found any example how to pass objective-C properties into a function for initialization. I know that it is possible with usual variables but there are no examples about what to do with properties.
You cannot pass an argument by reference in (Objective-)C. What you probably mean is to
pass the address of a variable as an argument to the method, so that the method can
set the value of the variable via the pointer.
However, this does not work with properties.
self.obj1 is just a convenient notation for the method call [self obj1], which returns
the value of the property. And taking the address of a return value is not possible.
What you can do is
Pass the address of the corresponding instance variables:
[SomeClass someFuncWithParam1:&_obj1 param2:&_obj2];
The disadvantage is that the property accessor methods are bypassed. That may or may not be
relevant in your case.
Pass the address of temporary local variables:
NSObject *tmpObj1;
NSObject *tmpObj2;
[SomeClass someFuncWithParam1:&tmpObj1 param2:&tmpObj2];
self.obj1 = tmpObj1;
self.obj2 = tmpObj2;
Both solutions are not very nice. Alternatively, you could pass the entire object (self) to the helper method, which then initializes both properties.
Or you define a custom class with just the properties obj1 and obj2, and make the helper method return an instance of this custom class.
I want to create a class in objective-c with its methods, so that for accessing the data I don't want to instantiate the class. how can I do it?
Either you can use singleton, or if you are planning to use only static methods, you can just add it in the class and use it directly with class name.
Create methods as static,
+(void)method;
then use it as,
[MyClass method];
This is helpful only if you are creating some utility classes which has only some utility method like processing an image or so. If you need to have property variables, you will need singleton.
For eg:-
Go to new file and create MySingleton class which will create MySingleton.h and MySingleton.m files.
In .h file,
#interface MySingleton : NSObject
{
UIViewController *myview;
}
#property (nonatomic, retain) UIViewController *myview;
+(MySingleton *)sharedSingleton;
In .m file,
+ (MySingleton*)sharedSingleton {
static MySingleton* _one = nil;
#synchronized( self ) {
if( _one == nil ) {
_one = [[ MySingleton alloc ] init ];
}
}
return _one;
}
- (UIViewController *)myview {
if (!myview) {
self.myview = [[[UIViewController alloc] init] autorelease]; //you can skip this, but in that case you need to allocate and initialize the first time you are using this.
}
return myview;
}
Then use it as,
[[MySingleton sharedSingleton] myview] anywhere in your project. Remember to import MySingleton.h though. Similarly you can create any object in singleton and use it. Just implement the getter or setter method accordingly.
One thing you have to be careful is that the object created in a singleton has only a single memory space allocated and hence it is the same object whenever you are using anywhere in your project. The above code will not create multiple copies of myview object in the class. So whenever you are modifying a property of myview that will be reflected everywhere. Use this approach only if it is absolutely needed and you need to have access to a single object from all over the project. Normally we use this only for situations like storing a sessionID which needs to be accessed from different classes etc..
You may use singleton pattern, check this question.
Like this:
+(MySingleton *)sharedInstance {
static dispatch_once_t pred;
static MySingleton *shared = nil;
dispatch_once(&pred, ^{
shared = [[MySingleton alloc] init];
shared.someIvar = #"blah";
});
return shared;
}
Or if you want to just access methods, you may use factory methods (those with +, not with -)
#interface MyClass
#property (nonatomic, assign) NSInteger value;
+ (void) factoryMethod;
- (void) instanceMethod;
...
// then in code
[MyClass factoryMethod]; // ok
[[MyClass sharedInstance] instanceMethod]; // ok
[MyClass sharedInstance].value = 5; // ok
UPDATE:
You may add a property to appDelegate
// in your app delegate.h
#property (nonatomic, retain) UIViewController* view;
// in your app delegate.m
#synthesize view;
and get appDelegate from almost any place like:
myapp_AppDelegate* appDelegate = [[UIApplication sharedApplicaton] delegate];
appDelegate.view = ...; // set that property and use it anywhere like this
Note, that you'll need to #import your UIViewController subclass and your appDelegate.h to make autocomplete work and sometimes avoid warnings.
// someFile.m
#import "appDelegate.h"
#import "myViewController.h"
...
myapp_AppDelegate* appDelegate = [[UIApplication sharedApplicaton] delegate];
appDelegate.view.myLabel.text = #"label text";
Does the following code call an accessor "set" function or does it modify the pointer myMember directly?
aClass.h
#interface MyClass : NSObject {
NSArray *myMember;
}
#property (nonatomic, retain) NSArray *myMember;
aClass.c
#implementation GameplayScene
#synthesize myMember;
- (id) init {
if ( (self = [super init]) )
{
myMember = [NSArray array];
}
}
In other words, I would like to know if the method setMyMember is being called, or if the pointer of myMember is being modified directly.
Likewise, is myMember = [NSArray array] identical to self.myMember = [NSArray array]?
Without the self. notation, the instance variable is modified directly. With it, the property setter is called (and since you made it a retain property, the new pointer that it's being set to will be sent a retain message).
See Apple's documentation on declaring and accessing properties.