CODEWITHSUNDEEP
iosobjective-c
BluGeni
BluGeni

Reputation: 3454

How to tell a viewcontroller to update its UI from another class

I am trying to understand how updating of a viewController that is currently visible works. I have ViewControllerA and ClassA. I want to tell ViewControllerA to reloadData on the tableview from ClassA. What is the best way to go about doing this?

I have found this question and answer but I dont think this will work in my situation or I am not understanding it correctly.

Upvotes: 3

Views: 1298

Answers (3)

Zeeshan
Zeeshan

Reputation: 4244

Key value Coding , NSNotificationCentre and Delegates are preferred. But NSNotificationCentre is easiest in your case.

The UIViewController that contains UITableView must add observer like this : Init :

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

In delloc method :

  [[NSNotificationCenter defaultCenter] removeObserver:self];

Post it from any XYZ class like on any UIButton action :

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

Advantage of NSNotificationCentre is that they can add observers in multiple classes ..

Upvotes: 1

danh
danh

Reputation: 62686

Answers here about using NSNotificationCenter are good. Be aware of a few other approaches:

A common one is the delegate pattern (see here and here).

Another is that the view controller observes the model change using KVO. (see here and here).

Another good one, often overlooked, which can probably be used in your case is the "do almost nothing" pattern. Just reloadData on your table view when viewWillAppear.

Upvotes: 2

random
random

Reputation: 8608

The easiest way without knowing your setup would be to use NSNotificationCenter. Here is what you could do:

In ViewControllerA add in hooks for NSNotificationCenter:

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];

    //Register for notification setting the observer to your table and the UITableViewMethod reloadData. So when this NSNotification is received, it tells your UITableView to reloadData
    [[NSNotificationCenter defaultCenter] addObserver:self.table selector:@selector(reloadData) name:@"ViewControllerAReloadData" object:nil];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    //Need to remove the listener so it doesn't get notifications when the view isn't visible or unloaded.
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

Then in ClassA when you want to tell ViewControllerA to reload data just post the NSNotification. 

- (void)someMethod {
    [[NSNotificationCenter defaultCenter] postNotificationName:@"ViewControllerAReloadData" object:nil];
}

Upvotes: 3

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