NSButton IBAction Crash unrecognized selector - objective-c

Question

Running into a simple problem and not quite sure what is causing it. Linked a NSButton up to a ViewController xib. The property is referenced and then I linked up the IBAction to the view controllers view. I'm getting a crash whenever I press the button with an unrecognized selector message. I know I'm doing something wrong but on iOS this is pretty standard.
Here is the code:
#import "AppDelegate.h"
#interface AppDelegate ()
#property (weak) IBOutlet NSWindow *window;
#end
#implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Insert code here to initialize your application
IPVLocationViewController *mainViewController = [[IPVLocationViewController alloc]initWithNibName:#"IPVLocationViewController" bundle:nil];
self.window.contentView = mainViewController.view;
}
- (void)applicationWillTerminate:(NSNotification *)aNotification {
// Insert code here to tear down your application
}
#end
#import "MainViewController.h"
#interface MainViewController ()
#property (weak) IBOutlet NSButton *mainButton;
#end
#implementation MainViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do view setup here.
}
- (IBAction)mainClick:(id)sender {
NSLog(#"THE BUTTON WAS CLICKED");
}
#end

Answer 1

In your Nib , it looks like your view controller instance is of type NSViewController instead of MainViewController.
So select the view controller in your Nib (or storyboard), and change its type to MainViewController.
Of course, if this view controller isn't being loaded from a nib or storyboard, then just check where you create it and make sure you created an instance of the correct class.

Answer 2

Solved it:
The accepted answer in this post helped me:
Needed to hold a reference to the view controller in the AppDelegate.
#interface AppDelegate ()
#property (nonatomic, strong) MainViewController *mainViewController;
#property (weak) IBOutlet NSWindow *window;
#end
#implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Insert code here to initialize your application
self.mainViewController = [[MainViewController alloc]initWithNibName:#"MainViewController" bundle:nil];
self.window.contentView = self.mainViewController.view;
}
- (void)applicationWillTerminate:(NSNotification *)aNotification {
// Insert code here to tear down your application
}
#end