I am setting up a Core Data model (UIManagedDocument) in my AppDelegate and was curious about how I might inject a reference to the NSManagedObjectContext into my (storyboards) Initial viewController.
I could access it directly in the viewControllers viewDidLoad using [[[UIApplication sharedApplication] delegate] sampleDatabase] managedObjectContext] and then pass it onto further controllers using prepareForSegue.
I was just wondering if there is an initial segue (or mechanism) that would allow me to pass (or inject) the managedObjectContext into that initial viewController without having to access it using the appDelegates shared instance once inside the controller?
When you use a storyboard, the initial view controller is set as the rootViewController property of your delegate just before application:didFinishLaunchingWithOptions: is called.
You should be able to use a cast on that reference to set a property, assuming your Core Data structure is set up by then.
Typically you would just have a property on the view controller that is a NSManagedObjectContext and just set that property right after you initialize the viewController in your appDelegate. myViewController.managedObjectContext = self.managedObjectContext
Related
I've got an app using Core Data where I'm creating a managedObjectContext in the app delegate.
I want to pass that managedObjectContext to two view controllers on my storyboard so they are using the same managedObjectContext to save and fetch to and from.
I can access the first view controller with:
self.window.rootViewController
But the second view controller I want to access is then after a segue from the first and no reference is returned from it.
I tried:
instantiateViewControllerWithIdentifier:
But that creates a new instance of the view rather than allowing me to access the second view controller that appears after the segue.
So my question is, how can I access the second view controller?
Or (as I'm very new to this) is there a better way to be managing/passing the data between the view controllers?
Thanks in advance.
Or (as I'm very new to this) is there a better way to be managing/passing the data between the view controllers?
It depends on the data you're trying to pass around. In this case, you want to give your view controllers access to your Core Data managed object context. Because this is something you're going to need throughout the lifespan of your app it would be better to have your view controllers access it via your application delegate.
You can do this via [[UIApplication sharedApplication] delegate] - however, you may need to typecast it to avoid compiler warnings, or alternatively you might want to create a macro that returns the managed object context to save you time and make your code a little more readable.
If you told XCode you wanted to use Core Data when you created the project you should have the methods to retrieve your object context already in your app delegate. If not, you'll need to create them.
To create a macro to save you having to write out [[UIApplication sharedApplication] delegate] every time you need to access the managed object context, check out this answer: Short hand for [[UIApplication sharedApplication] delegate]?
You can go through this :-
UINavigationController *navigationController = (UINavigationController *)self.window.rootViewController;
MasterViewController *result;
//check to see if navbar "get" worked
if (navigationController.viewControllers) {
//look for the nav controller in tab bar views
for (UINavigationController *view in navigationController.viewControllers) {
//when found, do the same thing to find the MasterViewController under the nav controller
if ([view isKindOfClass:[UINavigationController class]])
for (UIViewController *view2 in view.viewControllers)
if ([view2 isKindOfClass:[MasterViewController class]])
result = (MasterViewController *) view2;
}
}
I have a simple iOS application with one UIViewController beneath a UINavigationController. The UIViewController has an IBOutlet for an NSManagedObjectContext.
The AppDelegate has an IBOutlet for the nav controller - but not the view controller. The view controller is automatically instantiated ala the XIB process (as a child of the nav controller).
With this setup, how does one cleanly assign or pass the app delegate's NSManagedObjectContext to the view controller's IBOutlet property. There is a nav controller in the way :) and the app delegate doesn't have a direct property for the UIViewController.
It is a weird problem in that, I want to link a property from one XIB component to another component's property. Most of the XIB work I've done takes a property and points it to an object in the XIB which in turn - gets instantiated ala the normal process but in this case, the context is being created correctly in the app delegate, I just want to pass it on to the view controller when it instantiates it.
You don't need to pass it, just grab it from the app delegate as required:
#import "MyAppDleegate.h"
NSManagedObjectContext* moc = [(MyAppDelegate*)[UIApplication sharedApplication].delegate managedObjectContext];
Apple's docs recommend that you pass references to your managed object context to the classes the require them instead of referencing it from your app delegate.
Here's what the application:didFinishLaunchingWithOptions: looks like in one of my Core Data projects.
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
LocationsViewController *lvc = (LocationsViewController *)self.navigationController.topViewController;
lvc.managedObjectContext = self.managedObjectContext;
assert(lvc.managedObjectContext != nil);
[self.window addSubview:self.navigationController.view];
[self.window makeKeyAndVisible];
return YES;
}
You'll see that I also start with a UINavigationController with a single root view controller.
You've got the right idea, but the problem you're wrestling with seems to be entirely of your own creation. You say that your app delegate has an outlet for the navigation controller, but not for the nav controller's root view controller, because you've set up your nib such that the view controller is created when the nib is loaded. There's nothing wrong with that, but there's also no reason that the app delegate shouldn't have an outlet for that controller. Indeed, the entire reason for outlets is to get references to things that are loaded from a nib.
Add an outlet to your app delegate for your root view controller, and connect it. The app delegate can then give the controller a reference to the managed object context.
With respect to your question about multiple view controllers, I wonder what sort of real-world app might have view controller (A), which needs data, load another view controller (B) which doesn't need any data, followed by a third (C) which again needs data? A realistic example might help, if you have one.
Remember that you don't have to pass the entire managed object context to each successive view controller. You can instead pass just the part of the model that the controller will need to do its work by passing a managed object.
How to access a property value of AppDelegate class from someView Controller without creating reference of the delegate in view controller?
I'm not quite sure what you mean - there are multiple ways to get information from your application delegate into a view controller, and the phrase "without creating reference of the delegate" is unclear. Your options basically are:
Reference the application delegate, casting as appropriate. You would write code in your view controller class like: id propertyValue = [(MyAppDelegate *)[[UIApplication sharedApplication] delegate] myProperty];
Pass the property in when creating the view controller. This requires the view controller to have a #property declared and #synthesized for use, then you would have the app delegate just set the property on the view controller instance.
Neither of these options require that you retain a copy of your app's delegate as a #property, but the first does reference the delegate once.
[UIApplication sharedApplication].delegate
You'll also need to include the app delegate header file in your view controller and possibly typecast the delegate from id to your actual app delegate class.
#include "MyAppDelegate.h"
((MyAppDelegate *)[UIApplication sharedApplication].delegate).myProperty;
[UIApplication sharedApplication].delegate;
I have one single MainViewController which has of course it's one main UIView. I have this main view comprised of many different subviews.
Some of these subviews have their very own ViewController.
Lets say the MAIN view (whose delegate is primarily MainViewController) has a container which loads another UIView that uses a separate UIViewController- SecondaryViewController as the delegate for most it's actions.
This container view is of course loaded in MainViewController via
MyContainerViewController *myContainerController =
[[MyContainerViewController alloc] ...];
[self addSubView: myContainerController.view];
the controller for myContainerController.view though is MyContainerViewController. How inside this controller do I access MainViewController properties? Specifically I need to access MainViewController's - self.navigationController property to push a new ViewController? :)
Does this make any sense? I assume there's going to be casting of some sort involved since it seems I need to somehow retain a reference to MainViewController inside SecondaryViewController?
It doesn't make sense to push a new ViewController from the SecondaryViewController in the MainViewController.
This screws up the design of the code. A child object will access its parents method to call a method. By other words: bad code.
Make a delegate call from the SecondaryViewController to the MainViewController that it state has changed. Then the MainViewController can decide to do with the call and the SecondaryViewController will not know anything about the implementation of the MainViewController.
So:
Make a protocol in SecondaryViewController.
Let the MainViewController be SecondaryViewController's delegate.
Implement the delegate method in MainViewController which pushes the new ViewController.
Expose the desired sub-view controllers as properties of the view controller that contains them.
Expose your root view controller(s) as properties of your app delegate, and synthesize them also.
When you want to access a different UIViewController, first obtain a reference to your appDelegate:
MyAppDelegate* myAppDelegate = [[UIApplication sharedApplication] delegate];
Then just use your chain of properties to get access to your desired view controller.
SubSubViewController* ssvc = myAppDelegate.rootViewController.subViewController.subSubViewController;
Some folks frown upon the use of the sharedApplication class method to obtain the reference to a delegate, but I've used it in multiple apps and not suffered for it (yet). The alternative is to pipe your appDelegate through your hierarchy of viewControllers.
i know how to access appdelegate's value inside Viewcontroller like
YourDelegate *appDelegate = (YourDelegate *)[[UIApplication sharedApplication] delegate];
but i want simple method like this when i want to get value from viewcontroller to appdelegate(reverse order).....? any help...?
suppose if i have one method in appdelate. i want to get data value from view controller page,i want to use it in appdelegte.m file.......?
To address this question more generally...If you want to do anything with an object – send it a message (call a method on an object), access some property of an object, pass the object as a parameter to some other method – you need a reference to that object.
That means that, in your case, your AppDelegate needs a reference to the view controller you want to access some property of. If the view controller is allocated and initialized in your app delegate, this is as simple as storing a reference to said view controller in your delegate until you need to use it (using an instance variable or whatever). If it wasn't, then you need to do something else to get your app delegate a reference to the view controller – the steps to do this would depend on where and how the view controller was created. Without more specific details, I can't help you with those steps.
Model-View-Controller (MVC) Sidenote:
If you are following MVC design practices, a view controller (or any other controller class) is not the object that should be storing your state information or other application data. That job is supposed to be performed by a model object.
Make the method be a class method (declared with + (void) MyMethod: (int)myParameter) and call it from your app delegate like this: [MyOtherViewController MyMethod: myParameter].
This to call checkAppTheme method from AppDelegate.m :
[(AppDelegate *)[[UIApplication sharedApplication] delegate] checkAppTheme];
Don't miss to change (checkAppTheme) to your method in your AppDelegate.m
Good luck!