Updating Favorites List in Realtime iPhone

Introduction

As a developer, have you ever found yourself in a situation where you need to update data in real-time across different parts of an application? In this article, we’ll explore how to achieve this using notifications on an iPhone. We’ll take the example of updating a favorites list when the user switches between two tabs.

Background

In iOS development, notifications are a powerful tool for communicating between objects and sending events across the app domain. The NSNotificationCenter class is the foundation of notification services in iOS. When you post a notification, it’s received by any object that has subscribed to it using the addObserver:selector:name:object: method.

In our case, we have two tabs: one with a table view and another with an editor. We want to update the table view whenever new data is added to Core Data storage from the editor tab.

The Problem

Currently, the table view only updates when the app relaunches. This is because we’re getting the data in the viewDidLoad method of the table view controller. When we switch between tabs, their views are already loaded, so how can we update the table view in real-time?

Solution: Using Notifications

To solve this problem, we’ll use notifications to send updates from the editor tab to the table view when new data is added.

Adding Notification Service to Table View Controller

First, let’s add the notification service to our table view controller. We’ll start by adding an observer for notifications in the viewDidLoad method:

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(receiveAddNotification:) 
                                             name:@"AddNotification"
                                           object:nil];

This line tells the notification center to call the receiveAddNotification: method when it receives a notification with the name "AddNotification".

Receiving Notification in Table View Controller

Next, let’s define the receiveAddNotification: method:

-(void) receiveAddNotification: (NSNotification *)notification{
    if ([[notification name] isEqualToString:@"AddNotification"]){
        NSLog (@"Successfully received the add notification!");
        [self tableView reloadData]; // Reload the table view with new data
    }
}

This method checks if the notification is for the "AddNotification" name and, if so, logs a message to the console. It then reloads the table view using the reloadData method.

Posting Notification from Editor Tab

Now that we have the notification service set up, let’s post a notification from the editor tab when new data is added:

[[NSNotificationCenter defaultCenter] postNotificationName:@"AddNotification" object:self];

This line posts a notification with the name "AddNotification" and sends it to all observers, including our table view controller.

Putting It All Together

Here’s an example of how the code might look in both tabs:

Table View Controller

- (void)viewDidLoad {
    [super viewDidLoad];

    bList = [[NSMutableArray alloc] init];

    self.navigationItem.leftBarButtonItem = self.editButtonItem;

    // Some code to get data from Core Data storage and put them in the bList array.

    [[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(receiveAddNotification:) 
                                             name:@"AddNotification"
                                           object:nil];
}

-(void) receiveAddNotification: (NSNotification *)notification{
    if ([[notification name] isEqualToString:@"AddNotification"]){
        NSLog (@"Successfully received the add notification!");
        [self tableView reloadData]; // Reload the table view with new data
    }
}

Editor Tab

- (IBAction) addSomething {

    [[NSNotificationCenter defaultCenter] postNotificationName:@"AddNotification" object:self];
        // Some code to store an object in Core Data.
}

Conclusion

In this article, we explored how to update a favorites list in real-time across different parts of an iPhone app using notifications. We set up notification service in the table view controller and posted notifications from the editor tab when new data is added.

By following these steps, you can achieve similar results in your own apps. Remember to always keep your code organized and maintainable, and don’t hesitate to ask for help if you’re stuck!

Last modified on 2024-11-25