Objective-C: How to properly set didSelectViewController method for TabBarController, so I can refresh the VC everytime it is tapped

Question

Trying to accomplish

Tap on the tabbaritem and it will called the respective method on the tabbaritem VC.

Issue

When I

Answer 1

So the TabBarController can only have one delegate at a time. In the code you posted you're setting the tabBarController.delegate = self in each respective view controllers lifecycle method of viewDidLoad (called once when the view is first loaded). So whatever the last view controller is to load will be the final tabBarControllerDelegate.

Here's a very simple example to show what I mean:

FirstViewController

#import "FirstViewController.h"

@interface FirstViewController () <UITabBarControllerDelegate>

@end

@implementation FirstViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.tabBarController.delegate = self;
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"Who's my tab bar controller delegate = %@", self.tabBarController.delegate);
}

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController {
    NSLog(@"Delegate called on %@", NSStringFromClass([self class]));
}


@end

SecondViewController

#import "SecondViewController.h"

@interface SecondViewController () <UITabBarControllerDelegate>

@end

@implementation SecondViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.tabBarController.delegate = self;
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"Who's my tab bar controller delegate = %@", self.tabBarController.delegate);
}

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController {
    NSLog(@"Delegate called on %@", NSStringFromClass([self class]));
}

@end

If I run this and start by selecting the FirstViewController's tab, then select the SecondViewController's tab, then go back to selecting the FirstViewController's tab this is the log result I get:

First Tab Selected:
Who's my tab bar controller delegate = <FirstViewController: 0x7ff9eb406970>
Delegate called on FirstViewController

Second Tab Selected:
Who's my tab bar controller delegate = <SecondViewController: 0x7fa33ac0a540>
Delegate called on FirstViewController (this is still FirstViewController here because the tab bar selection occurred prior to setting the SecondViewController to the tabBarControllerDelegate)

First Tab Selected:
Who's my tab bar controller delegate = <SecondViewController: 0x7fa33ac0a540>
Delegate called on SecondViewController

Second Tab Selected:
Who's my tab bar controller delegate = <SecondViewController: 0x7fa33ac0a540>
Delegate called on SecondViewController

...
 and it continues on that the SecondViewController will remain the delegate

So my recommendation would be to use a different pattern that just maintains one coordinator to handle the TabBarDelegation.

Edit in response to your comment about other recommendations

A rather standard idiom in iOS is loading your data from the server once (usually in viewDidLoad of the respective view controllers then storing it), then having a pull to refresh control which allows users to refresh the data on command: https://medium.com/ios-os-x-development/ios-tips-pull-to-refresh-in-less-than-30-seconds-ef884520f0df If you definitely require the tab bar delegate to do something on each view controller selection, I'd recommend having one central object that is the only tab bar delegate and having it handle what tasks to do based on the view controller passed in through the delegate method tabBarController:didSelectViewController: as one additional example.