如何将另一个视图控制器的数组保存到应用程序委托中的文件中？

Question

I have an array in my root view controller that I need to save (using core data) whenever applicationDidEnterBackground is called. How can I send a message to an instance of the root view controller within the delegate?

I was thinking about giving the delegate a reference to view controller when it's set as the root, but that feels inefficient. Is there a better way to do this?

Answer 1

In your root view controller register to receive the ApplicationWillEnterBackground notification. The root view controller can then perform a save when it receives this notification.

Your initial instinct to reduce coupling between controllers was a good one.

Answer 2

1) In your RootViewController .h file,

+ (RootViewController *) sharedStore;

2) In your RootViewController .m file,

+ (RootViewController *) sharedStore
{
    static RootViewController *myStore = nil;

    if (!myStore) {
        myStore = [[RootViewController alloc] init];
    }
    return myStore;
}

3) Go to your AppDelegate.m file and import your RootViewController

#import RootViewController.h

4) In your AppDelegate.m file, go to the ApplicationDidEnterBackground method and type:

[[RootViewController sharedStore] saveChanges];

5) Implement the saveChanges method in RootViewController.

Answer 3

AJ112's answer makes:

• A singleton from a UIViewController , which is not a good practice.
• Creates coupling with your UIApplication , which is something to avoid as much as possible.

There are some UIApplication notifications that you can observe from whatever class you need to handle multitasking. Check the answer on this SO question:

iphone 4 sdk : detect return from background mode

You can check all the notifications that UIApplication posts in here:

http://developer.apple.com/library/ios/DOCUMENTATION/UIKit/Reference/UIApplication_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006728-CH3-DontLinkElementID_4