iOS passing Data from AppDelegate to UITabBarController

robbieduncan said:

Do it the other way round. Any instance can get a pointer to the app delegate so simply provide an accessor method for the data model there.

Or make the "root" of your data model a singleton object and access it that way.

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// MyController.h

@class MyModel;

@interface MyController : UITableViewController {
  MyModel *model;
}
@property (nonatomic, retain) MyModel *model;
@end

// MyController.m

#import "MyModel.h"

@implementation MyController
@synthesize model;
@end

// YourAppDelegate.m

- (void)applicationDidFinishLaunching:(UIApplication *)application 
{
  Model *someModelInstance = [[MyModel alloc] init];
  MyController *controller = [[MyController alloc] initWithStyle:UITableViewStylePlain];
  controller.model = someModelInstance;
  [someModelInstance release];
  [window addSubview:controller.view];
  [controller release];
  [window makeKeyAndVisible];
}

Luke Redpath said:

Mmm, whilst sometimes necessary, making everything singletons or accessing the app delegate all over the place seems like a code smell to me.

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Luke Redpath said:

Mmm, whilst sometimes necessary, making everything singletons or accessing the app delegate all over the place seems like a code smell to me.

If you need to pass data into your controller from your app delegate, just add an accessor (or a property) to your own subclass of UITableViewController, e.g.:

Code:

// MyController.h

@class MyModel;

@interface MyController : UITableViewController {
  MyModel *model;
}
@property (nonatomic, retain) MyModel *model;
@end

// MyController.m

#import "MyModel.h"

@implementation MyController
@synthesize model;
@end

// YourAppDelegate.m

- (void)applicationDidFinishLaunching:(UIApplication *)application 
{
  Model *someModelInstance = [[MyModel alloc] init];
  MyController *controller = [[MyController alloc] initWithStyle:UITableViewStylePlain];
  controller.model = someModelInstance;
  [someModelInstance release];
  [window addSubview:controller.view];
  [controller release];
  [window makeKeyAndVisible];
}

Of course, I'm making assumptions about where your instance of your model comes from and where the controler is initialized (it might be loaded from a nib into an instance variable/property of your app delegate).

Click to expand...

Luke Redpath said:

Mmm, whilst sometimes necessary, making everything singletons or accessing the app delegate all over the place seems like a code smell to me.

Click to expand...

samsonsu said:

Saving & initializing model in view controller could be a problem if you have multiple views in your app. Upon low memory warning, view controller might re-init (if it's not the current view controller), and that causes your data model to re-create and you lose all the state.
.

Click to expand...

firewood said:

And for a small app with a countably small number of objects and models, wasting a users memory and battery life by using layers of properties, subclasses, and notification handlers seems like an even smellier waste of resources to me.

Just stick a pointer to the model in a global. Or if the apps total state data is small enough, just put them all in global variables. One less level of indirection to potentially trash your CPU cache.

Not every class needs to be designed to scale to 1000's of instances collaborating remotely. Remember that all this dynamic OOP stuff, while good for the developer, can be bad for the users battery life. Spend some time thinking about them.

imho

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