How to save data to NSMutableDictionary and load data from NSMutableDictionary - ios

Question

I am trying to create shopping cart. I want to put all data NSMutableDictionary from NSDictionary with Bar-code number which has DataItem variable as key. I have created NSMutableDictionary with that code block;
- (void)viewDidLoad {
[super viewDidLoad];
DataItem = [[[_response objectForKey:#"Data"] objectForKey:#"Items"] objectForKey:#"Item"];
NSMutableDictionary *CartItems = [[NSMutableDictionary alloc]init];
for(NSDictionary *transaction in DataItem)
{
[CartItems setValue:transaction forKey:[transaction objectForKey:#"BarcodeNumber"]];
}
}
When I push another viewController for selection another item to put cart. Once again,push that viewController, it deletes before item from CartItems variable.
I know I have putted that code block NSMutableDictionary *CartItems = [[NSMutableDictionary alloc]init]; inside of viewDidLoad. That's why, It generates new CartItems variable. If I want to put it .h file, it returns nil. I did not find any solution.
Is there any way to load data to NSMutableDictionary for reusing? or Is there another way to create same logic? Thanks.

Answer 1

use a singleton class to store you data like this tutorial

Answer 2

Make a singleton class for data which returns same object with first time initialization and use that for storing your data.
+ (id)getBE {
static MyBEClass *objMyBEClass = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
objMyBEClass = [[self alloc] init];
});
return objMyBEClass;
}
Make CarItems dictionary a property of BE class so you can get this from your view controller.
#property(strong)NSMutableDictionary *CartItems;
In init method of BE class initialize your array/dictionary.
CartItems = [[NSMutableDictionary alloc]init];

Answer 3

You can manage this by using NSUserDefaults. Here is viewDidLoad-
- (void)viewDidLoad {
DataItem = [[[_response objectForKey:#"Data"] objectForKey:#"Items"] objectForKey:#"Item"];
NSUserDefaults *prefrence=[[NSUserDefaults alloc]init];
if ([[NSUserDefaults standardUserDefaults]objectForKey:#"cartItems"]!=nil) {
NSMutableDictionary *CartItems=[[NSUserDefaults standardUserDefaults]objectForKey:#"cartItems"];
for(NSDictionary *transaction in DataItem)
{
[CartItems setValue:transaction forKey:[transaction objectForKey:#"BarcodeNumber"]];
}
[prefrence setObject:CartItems forKey:#"cartItems"];
}else{
NSMutableDictionary *CartItems = [[NSMutableDictionary alloc]init];
for(NSDictionary *transaction in DataItem)
{
[CartItems setValue:transaction forKey:[transaction objectForKey:#"BarcodeNumber"]];
}
[prefrence setObject:CartItems forKey:#"cartItems"];
}
}
whenever you want to clear your cart that time also clear NSUserDefaults using [[NSUserDefaults standardUserDefaults]removeObjectForKey:#"cartItems"].

Answer 4

I would not suggest to use a Singleton for such a thing except if your building a huge app with many controllers, and you need your chart everywhere.
If it's not the case, I would suggest you to pass the char as parameter from one controller to the other one, and pass it back with a delegate as in this guide.
if you have an application built with a single navigation controller, remember that it is not deallocated, so you can save data there. Just make getters and setters of your variable visible (.h file) or the variable itself, but remember that that is not a very good practise because it looks like it will be modified by many controllers, and thats another reason why you should avoid using singletons.
Hope it helps!