Bind RACComand to UIViewController event - ios

Question

I'm implementing RAC with MVVM pattern in my project and now I came into a doubt.
I have many calls to the server, but all of them are associated to an UIButton and handled in my ViewModel; now I need to make a call to the server when the UIViewController is loaded. Before MVVM I just created a signal in the viewDidLoad method an voilá!, but I'm not sure if is ok to put this in the ViewController.
Now I don't know how to bind a RACSignal to an event in my ViewController, and worst of that, I'm not sure if that is the way following the MVVM pattern.
What I'm doing right now when I make a call to server coming from a user action(from a UIButton) is this:
ViewController*
self.someButton.rac_command = viewModel.executeSomeAction
//On success:
self.viewModel.executeLoginCompleted.skip(1).subscribeNextAs {
(isExecuting: Bool) -> () in
//Do something
}
//On error:
self.viewModel.executeSomeActionError.subscribeNextAs {
(error: NSError) -> () in
//Dd something
}
ViewModel*
var executeSomeAction: RACCommand?
var executeSomeActionError: RACSignal!
var executeLoginCompleted: RACSignal
executeSomeAction = RACCommand(enabled: combineValidationSignals) {
(any:AnyObject!) -> RACSignal in
println("ANY: \(any)")
return self.executeLoginRequest()
}
executeSomeActionError = executeLogin!.errors
executeLoginCompleted = executeLogin!.executing
How should I create a RACSignal or RACCommand when the UIView did load? Of course, following the MVVM pattern.
Thanks

Answer 1

You have two options. One more hacky than the other but easier to implement accross your app.
Option 1:
You can write an extension to UIViewController that uses associatedObjects to add a viewDidLoadCommand: RACCommand property to UIViewController. You then swizzle the viewDidLoad() method of UIViewController so that it executes your command on viewDidLoad():
extension UIViewController {
private struct AssociatedKeys {
static var ViewDidLoadCommand: String = "ViewDidLoadCommand"
}
var viewDidLoadCommand: RACCommand? {
get {
return objc_getAssociatedObject(self, &AssociatedKeys.ViewDidLoadCommand) as? RACCommand
}
set {
if let newValue = newValue {
objc_setAssociatedObject(
self,
&AssociatedKeys.ViewDidLoadCommand,
newValue as RACCommand?,
UInt(OBJC_ASSOCIATION_RETAIN_NONATOMIC)
)
}
}
}
func swizzled_viewDidLoad() {
self.swizzled_viewDidLoad()
self.viewDidLoadCommand?.execute(nil)
}
}
// In the appDelegate
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
// Override point for customization after application launch.
method_exchangeImplementations(
class_getInstanceMethod(UIViewController.self, "viewDidLoad"),
class_getInstanceMethod(UIViewController.self, "swizzled_viewDidLoad"))
return true
}
Option 2
You can just subclass UIViewController and implement the viewDidLoadCommandand call it in viewDidLoad()
class ViewControllerSubClass : UIViewController {
var viewDidLoadCommand: RACCommand?
override func viewDidLoad() {
super.viewDidLoad()
self.viewDidLoadCommand?.execute(nil)
}
}
Whichever method you choose all you have to do then is set the command in the your custom viewControllers init method and and it will get executed on viewDidLoad.