iPhone UITableView trigger a parent method?

Question

Okay, so I'm working on an iPhone app with a preferences-esque section where there's a base TableView, which has one section, and several rows of customized cells to hold a name and a value label. Clicking on a row brings up another View, which allows the user to pick from a list (another TableView), and select an item.

All of these TableViews are done programatically. The base TableView has a property that holds a Controller instance for each of the "pick from the list" Views. Each of the "pick from the list" views has a property called chosenValue that has the currently-selected option. I've gotten the UI to handle the didSelectRowAtIndexPath to update the chosenValue property and then "pop" the view (going back to the main TableView). But, even though the main TableView's cellForRowAtIndexPath method references the chosenValue property of the subview that's held in a property, the view doesn't update when an item is selected. In short, how can the sub-view trigger a reloadData on the parent object, after it "pops" and unloads?

Answer 1

You should define a delegate for that. In the child TableView define a protocol:

@protocol ChildViewControllerDelegate
- (void) somethingUpdated;
@end

Also define a property for a delegate implementing this protocol:

id <ChildViewControllerDelegate> delegate;

Then in Parent all you need to do is to define a method somethingUpdated, assign itself (parent) to a delegate property in Child and call this method in Child view when you need to update it. Implementation of somethingUpdated in Parent can be different based on what you're trying to accomplish.

Answer 2

You could realize this using the notifications or delegation, for example.

Using notifications your first view controller has to register for a notification like this:

…

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

…

- (void)methodToBeCalled:(NSNotification *)notification { 
    [self.tableView reloadData];
    // do something else
}

Then you can raise a notification in your second view controller like this:

[[NSNotificationCenter defaultCenter] postNotificationName:@"myNotification" object:nil];

Using delegation you could implement a property for a delegate on the second view, set that to self before pushing the second view controller and call a method on the delegate when needed.