I have the following snippet and a call to the method is not working!
#interface myVM(){
NSArray *results;
}
#property (nonatomic, strong) MyModel *model;
#end
#implementation myVM
- (instancetype)initWithItems{
self = [super init];
if (!self) return nil;
**[self.model loadInfo];**
_DeviceNameArray = self.model.DeviceNames;
}
What is the reason for the method being not called?
You have to allocate and initialize it first:
- (instancetype)initWithItems{
self = [super init];
if (!self) return nil;
self.model = [MyModel new]; // like this
[self.model loadInfo];
_DeviceNameArray = self.model.DeviceNames;
return self;
}
self.model is not initialized. If you debug it, you will see it is nil.
By the time you are calling [self.model loadInfo];, the model property has not been set yet and is nil. You probably want something like:
- (instancetype)initWithModel:(MyModel *)aModel {
self = [super init];
if (!self) return nil;
self.model = aModel;
[self.model loadInfo];
_DeviceNameArray = self.model.DeviceNames;
return self;
}
You should structure your custom init methods like this for better readability.
- (instancetype)initWithItems
{
self = [super init];
if (self) {
[self.model loadInfo];
_DeviceNameArray = self.model.DeviceNames;
}
return self;
}
The problem is that self.model has not been initialised anywhere. It is just a property that contains no information - it is nil. You need to assign something to it somewhere.
E.g., pass a model object as parameter like so, initWithItem:(MyModel *)model, then assign it to self.model.
Related
I am trying to add objects to a NSMutableArray from another class and it won't work. It works perfectly for the other attribute.
I looked at similar questions but couldn't find a suitable answer.
The object iPack :
#interface IPack : NSObject
#property float price;
#property NSMutableArray *cocktails;
#end
In the class of my collection view :
- (void)viewDidLoad {
[super viewDidLoad];
self.iPack = [[IPack alloc] init];
self.iPack.cocktails = [[NSMutableArray alloc] init];
In the class of my cell :
self.collectionView.iPack.price = self.price //perfectly works
NSArray* cock = [NSArray arrayWithObjects:c1,c2,c3,c4,c5, nil];
[self.collectionView.iPack.cocktails addObjectsFromArray:cock]; //line won't work
You haven't shown the [IPack init] method, but I strongly suspect you are not allocating the cocktails array. Simply defining it as a property does not mean it's automatically allocated:
#implementation IPack
- (instancetype)init
{
self = [super init];
if (self) {
_price = 0.0f;
_cocktails = [NSMutableArray new];
}
return self;
}
#end
EDIT
I've just seen this line in your question:
self.iPack.cocktails = [[NSMutableArray alloc] init];
Which would suggest my answer is wrong (despite it being the better way of doing the same thing). Sorry about that; I cannot see why your code doesn't work. Are you sure you are checking correctly?
try this,
in IPack class add a method
#interface IPack : NSObject
#property float price;
#property NSMutableArray *cocktails;
- (instancetype)initWithPrice:(float)price cocktails:(NSMutableArray *)cocktails;
#end
and in implementation
#implementtion IPack
- (instancetype)initWithPrice:(float)price cocktails:(NSMutableArray *)cocktails {
self = [super init];
if (self) {
self.price = price;
self.cocktails = cocktails;
}
}
#end
In the class of my collection view :
remove alloc init in viewDidLoad
that is remove the following lines
self.iPack = [[IPack alloc] init];
self.iPack.cocktails = [[NSMutableArray alloc] init];
In the class of my cell :
NSArray* cock = [NSArray arrayWithObjects:c1,c2,c3,c4,c5, nil];
IPack *ipack = [[IPack alloc] initWithPrice:self.price cocktails:[NSMutableArray arrayArray:cock]];
self.collectionView.iPack = ipack;
Just want to ask if this method initWithNibName ends, will the logInIDArray and passwordArray property become nil again?
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
//sharedLogInDataBase returns singleton
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
BNRLogInDataBase *logInDatabase = [BNRLogInDataBase sharedLogInDataBase];
logInDatabase.logInIDArray = [[NSMutableArray alloc]init];
logInDatabase.passwordArray = [[NSMutableArray alloc]init];
}
return self;
}
here's the singleton method
+(instancetype)sharedLogInDataBase
{
static BNRLogInDataBase * database = nil;
if (!nil) {
database = [[BNRLogInDataBase alloc]initPrivate];
}
return database;
}
-(instancetype)init
{
#throw [NSException exceptionWithName:#"Singleton" reason:#"use sharedLogInDataBase" userInfo:nil];
}
-(instancetype)initPrivate
{
self = [super init];
return self;
}
Your method should be:
+ (instancetype)sharedLogInDataBase
{
static dispatch_once_t once;
static id sharedInstance;
dispatch_once(&once, ^{
sharedInstance = [[self alloc] init];
});
return sharedInstance;
}
Currently your if (!nil) is not doing what you expect it to...
Then, your init method should call your initPrivate method.
They cannot become nil because you instantiated them. Though they will be empty.
It will depends on:
How you implemented your BNRLogInDataBase singleton, if you use a strong reference to keep the singleton instance logInDatabase will stay, if not it will be deallocated
How you declared logInIDArray and passwordArray properties, if strong they will remain as long as logInDatabase exists, if weak they will become nil
if (!nil) {
database = [[BNRLogInDataBase alloc]initPrivate];
}
Check your test, nil is always false, so !nil is always true, each time you call your singleton you get a different object !
So I know my problem is that my transfer array is not being initialized correctly. Where should I put transfer = [[NSMutableArray alloc] init];?
#interface PictureViewController (){
Poi *labelPoi;
}
#end
#implementation PictureViewController
#synthesize imageX;
#synthesize imageY;
#synthesize name;
#synthesize transfer;
- (id)init
{
self = [super init];
if(self) {
transfer = [[NSMutableArray alloc] init];
}
return self;
}
-(id)initWithLabel:(double)imageX andY:(double)imageY withName:(NSString *)name{
self = [super init];
if(self){
// transfer = [[NSMutableArray alloc] init];
self.imageX = imageX;
self.imageY = imageY;
self.name = name;
}
return self;
}
/*-(id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if(self){
transfer = [[NSMutableArray alloc] init];
self.imageX = imageX;
self.imageY = imageY;
self.name = name;
NSLog(#"imageX: %f", self.imageX);
NSLog(#"imageY: %f", imageY);
NSLog(#"name: %#", name);
}
return self;
}*/
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
NSLog(#"transfer count: %lu",(unsigned long)transfer.count);
for(int i = 0; i < transfer.count; i++){
UILabel *label = [[UILabel alloc] initWithFrame: CGRectMake([[transfer objectAtIndex:i] imageLocationX], [[transfer objectAtIndex:i] imageLocationY], 200, 50)];
label.text = [[transfer objectAtIndex:i] name];
label.font = [UIFont systemFontOfSize:14];
label.backgroundColor = [UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.0];
[self.view addSubview:label];
NSLog(#"asdfasdsd");
}
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (id)display:(double)imageXX andY:(double)imageYY withName:(NSString *)namee{
NSLog(#"%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%");
NSLog(#"imageX: %f",imageXX);
NSLog(#"imageY: %f", imageYY);
NSLog(#"name: %#", namee);
labelPoi = [[Poi alloc] init];
//transfer = [[NSMutableArray alloc] init];
labelPoi.imageLocationX = imageXX;
labelPoi.imageLocationY = imageYY;
labelPoi.name = namee;
[transfer addObject:labelPoi];
NSLog(#"label.x: %f should be: %f", labelPoi.imageLocationX, imageXX);
NSLog(#"label.y: %f should be: %f", labelPoi.imageLocationY, imageYY);
NSLog(#"label.name: %# should be: %#",labelPoi.name,namee);
NSLog(#"transssssfer: %lu", (unsigned long)transfer.count);
NSLog(#"asfddfsaasfdfdsfsd %f", [[transfer objectAtIndex:0] imageLocationX]);
return self;
}
#end
The Poi object is made up of an imageLocationX, imageLocationY, and name and I am trying to put the Poi object into an array named transfer however, whenever I try to access transfer elements, I receive 0 or null. The (id)display function is being called several times from a different view NSMutable alloc in that function, the array gets reset.
Here is the output:
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] %%%%%%%%%%%%%%%%%%%%%%%%
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] imageX: 224.485718
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] imageY: 116.353401
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] name: Beutel Student Health Center
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] label.x: 224.485718 should be: 224.485718
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] label.y: 116.353401 should be: 116.353401
2013-07-19 11:22:06.736 AR_UAV_App[12466:11303] label.name: Beutel Student Health Center should be: Beutel Student Health Center
2013-07-19 11:22:06.737 AR_UAV_App[12466:11303] transssssfer: 0
2013-07-19 11:22:06.737 AR_UAV_App[12466:11303] asfddfsaasfdfdsfsd 0.000000
2013-07-19 11:22:06.737 AR_UAV_App[12466:11303] #############################################################
EDIT: .h file
#interface PictureViewController : UIViewController{
NSMutableArray *transfer;
}
#property (nonatomic) double imageX;
#property (nonatomic) double imageY;
#property (nonatomic) NSString *name;
#property (nonatomic,retain) NSArray *transfer;
- (IBAction)backView:(id)sender;
- (IBAction)load:(id)sender X:(double)imageX andY:(double)imageY withName:(NSString *)name;
-(id)initWithLabel:(double)imageX andY:(double)imageY withName:(NSString *)name;
-(id)display:(double)imageX andY:(double)imageY withName:(NSString *)name;
#end
This init method should become the "designated" initializer:
-(id)initWithLabel:andY:withName:(NSString *)name
(by the way, it's not named correctly according the naming conventions)
The designated initializer shall initialize the instance properly (that is, in your case it may initialize the array transfer, unless you use a lazy accessor ).
The "designated initializer" is most often the "most specialized" initializer - that is, that one with the most parameters. Most often, there is only one and easily identifiable designated initializer.
The "designated initializer" has the canonical form:
-(id)initWithLabel:(double)imageX andY:(double)imageY withName:(NSString *)name{
self = [super init];
if(self){
// initialization
...
}
}
Other init methods like the init method shall invoke the designated initializer like:
- (id)init {
return [self initWithLabel:0 andY:0 withName:#""];
}
I guess one problem can be that when you are creating this controller you are calling to:
-(id)initWithLabel:(double)imageX andY:(double)imageY withName:(NSString *)name
In case you do that, you are calling to [super init] what will never go through the init method of your class (where you allocated the array). In case you have different methods to init a controller I recommend you to have a:
commonInit{
_transfer = [[NSMutableArray] alloc] init];
}
Then call this method for every init method that you have in your controller so you ensure that array is allocated.
Other thing is just allocate your array in the viewDidLoad of your controller.
Just for making know, you can "allocated" an array without having to take care about release the object by calling to [NSMutableArray arrayWithCapacity:0];
Are you initializing your PictureViewController with -(id)initWithLabel:(double)imageX andY:(double)imageY withName:(NSString *)name? If so, I can tell you what the problem is...
-(id)initWithLabel:(double)imageX andY:(double)imageY withName:(NSString *)name
{
self = [super init]; // <--- You are likely confused about this line
.....
}
[super init] does not pass a message to your custom -(id)init method. It instead is referring to PictureViewController's superclass, which is likely UIViewController.
Your problem should be fixed by uncommenting transfer = [[NSMutableArray alloc] init]; in the initWithLabel: custom init method.
make a property (synthesize it #synthesize transfer=_transfer;), use lazy instantiation like:
-(NSMutableArray*)transfer
{
if (!_transfer)
{
_transfer=[NSMutableArray array];
}
return _transfer;
}
and take it out of your init
I have a #property (nonatomic,retain) NSMutableArray *transfer_array; in .h file and in my .m I have
#synthesize transfer_array = _transfer_array;
- (id)init
{
self = [super init];
if(self) {
self.transfer_array = [[NSMutableArray alloc] init];
}
return self;
}
and I add objects to the array in this function
- (id)display:(double)imageXX andY:(double)imageYY withName:(NSString *)namee{
//if((self == [super init])){
NSLog(#"````````````````````````````````````````````````````````");
NSLog(#"imageX: %f",imageXX);
NSLog(#"imageY: %f", imageYY);
NSLog(#"name: %#", namee);
labelPoi = [[Poi alloc] init];
labelPoi.imageLocationX = imageXX;
labelPoi.imageLocationY = imageYY;
labelPoi.name = namee;
[self.transfer_array addObject:labelPoi];
The objects add successfully bu whenever I try to access the array elements in another instance such as:
- (void)viewDidLoad{
[super viewDidLoad];
NSLog(#"transfer_array count: %lu",(unsigned long)self.transfer_array.count);
Then the array is empty.
Any help would be appreciated!
Instances are independent objects. Changing the internal state of one doesn't affect the internal state of others.
I have created a single ton like this for ARC,
+ (MyClass *)sharedInstance {
static MyClass *sharedSpeaker = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedSpeaker = [[self alloc] init];
});
return sharedSpeaker;
}
- (id)init {
if (self = [super init]) {
}
return self;
}
But here I am creating instances like this:
id speaker3 = [[MyClass alloc] init];
id speaker = [MyClass sharedInstance];
id speaker2 = [[MyClass alloc] init];
NSLog(#"Speaker 1= %# \n speaker 2 = %#\n Speaker3 = %#",speaker,speaker2,speaker3);`
I got output as:
Speaker 1= <MyClass : 0xa45f5e0>
speaker 2 = <MyClass : 0xa461740>
Speaker3 = <MyClass : 0xa4529e0>
This is looking like a desired behaviour. How to stop this when I am giving singleton in library to user. I need to block him from creating new instance. Do I need to make static global if I make it global he cant create the global variable of the same name there will be conflict right. So any memebers can give solution on this?
For example using an assert in the init method.
- (id)init {
static int maxInstances = 1;
assert(maxInstances > 0);
maxInstances--;
...
}
Because you are creating new instances of your singleton class using alloc, init.
You will get the singleton instance using the sharedInstance class method. Like:
id speaker = [MyClass sharedInstance];
If you don't want to create the instances with alloc or init. Override those methods.
You can write static MyClass *sharedSpeaker = nil; as a static global variable and remove it from the sharedInstance method.
in .h file
#import <Foundation/Foundation.h>
#interface Singleton : NSObject
{
///......
}
+ (Singleton *)sharedSingleton;
in .m file
#import "Singleton.h"
#implementation Singleton
static Singleton *singletonObj = NULL;
+ (Singleton *)sharedSingleton
{
#synchronized(self)
{
if (singletonObj == NULL)
singletonObj = [[self alloc] init];
}
return(singletonObj);
}
and use this in another file
#import "Singleton.h"
//.....
Singleton *sinObj = [Singleton sharedSingleton]; // not alloc and init. use direct
create instance like this it will always return you singlton
static testSinglton *myinstance = nil;
+ (testSinglton *) sharedInstance {
if (!myinstance) {
myinstance = [[testSinglton alloc] init];
}
return myinstance;
}
- (id) init {
if (myinstance) {
return myinstance;
}
if (self = [super init]) {
//new object now will be created...
myinstance = self;
}
return self;
}
NSLog(#"%#",[[testSinglton alloc] init]);
NSLog(#"%#",[testSinglton sharedInstance]);
NSLog(#"%#",[[testSinglton alloc] init]);