passing data between tabs in iOS - objective-c

Question

it is my first app that I am trying to do on my own and I have some questions. I want to have 4 tabs, and in the first one named "HomeView" I am parsing JSON data (this is done so far).
But what I want is some of the data that are being parsed to be visible in other tabs (and not have to parse them again).
So parts of my code of HomeView is here:
#import "HomeView.h"
#interface HomeView ()
#end
#implementation HomeView
//other code
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//data fetched
parsed_date=[res objectForKey:#"date"];
NSLog(#"Date:%#",parsed_date);
[UIAppDelegate.myArray addObject:parsed_date];
}
and I can see the "parsed_date" being printed out correctly.
So I want this parsed_date to be visible in OtherView.
This is my code but I cannot print it out.
OtherView.m
#import "OtherView.h"
#import "HomeView.h"
#import "AppDelegate.h"
#interface OtherView ()
#end
#implementation OtherView
#synthesize tracks_date;
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
//preview value of other class
tracks_date = [UIAppDelegate.myArray objectAtIndex:0];
NSLog(#"Dated previed in OtherView: %#", tracks_date);
}
and (null) is being printed out.
added code of app delegate.h
#import <UIKit/UIKit.h>
#define UIAppDelegate ((AppDelegate *)[UIApplication sharedApplication].delegate)
#interface AppDelegate : UIResponder <UIApplicationDelegate>
#property (strong, nonatomic) UIWindow *window;
#property (nonatomic, strong) NSArray *myArray;
#end
So can you suggest me a sollution?

Answer 1

Add the property to your Application Delegate instead.
When assigning the property do something like:
MyAppDelegate *delegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
delegate.myProperty = #"My Value";
then, in your different tabs, you can retrieve this property in the same manner:
MyAppDelegate *delegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
NSString *valueInTab = delegate.myProperty;

Answer 2

Uh, when you create a HomeView in your last code segment there, you're creating a new object -- a new instance of the class. It will not contain the data from connectionDidFinishLoading unless that method is executed in that instance of the class.
You basically need to use some sort of persistence mechanism to do what you want, either the AppDelegate or static storage along the lines of a "singleton".

Answer 3

While this may not be the best method of doing this, it is easy and effective.
Save your data in your app delegate and retrieve it from there. You can create a shortcut to your app delegate shared application. Then just access the values there.
AppDelegate.h
#define UIAppDelegate ((AppDelegate *)[UIApplication sharedApplication].delegate)
#property (nonatomic, strong) NSArray *myArray;
TabView1.m
#import "AppDelegate.h"
SomeObject *myObject = [UIAppDelegate.myArray objectAtIndex:0];
Like I said, it might not be the best way to organize your data for your application, this method does work for small amounts of data needing to be shared at the application level. Hope this helps.

Answer 4

this happens because you create an instance of HomeView yourself.
it has simply no connections to anything.
your first example works because it is the created and initialized from your nib.
i think the best way is to use an IBOutlet and then connect both 'Views' in InterfaceBuilder.
#interface OtherView ()
IBOutlet HomeView *homeView;
#end
#implementation OtherView
#synthesize tracks_date;
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(#"Dated previed in OtherView: %#", homeView.parsed_date);
}
- (void)dealloc:
{
[homeView release];
}
have a look here, it will demonstrate it much more
In InterfaceBuilder you can manage your Objects and connect them (via IBOutlets and IBAction, ...) together.
I think this video is a good demonstration how this concept work.