Calling swift animation from completion event? - ios

Question

I am trying to call an animation event on a FBSDKLoginButton in swift. I can tell the animation is being call, because the elements that are changing alpha values function correctly. For some reason though, the button will not move in the same call.
If I touch another button, calling the exact same function, the button then moves. Not sure why calling a function from a completion event vs. another location would affect whether or not the object actually moves?!
Under the BTN_Animate, that where the call works. After the
LocalProfile.sharedInstance.updateFromFacebook(updateFromFacebook_Complete:
call you can see the same function, and the argument being passed is assumed true.
#IBAction func BTN_Animate(_ sender: Any) {
animateScreen(loggedIn: true) //Call that works
}
public func loginButton(_ BTN_facebookLogin: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {
print("> Attempting Login from Main View Controller")
if ((error) != nil)
{
print("Error: ")
// Process error
print(error)
}
else if result.isCancelled {
// Handle cancellations
print("Request cancelled")
print(result)
}
else {
// If you ask for multiple permissions at once, you
// should check if specific permissions missing
LocalProfile.sharedInstance.updateFromFacebook(updateFromFacebook_Complete: {
self.LBL_Name.text = LocalProfile.sharedInstance.firstName
self.IMG_ProfilePicture.image = LocalProfile.sharedInstance.profilePicture
LocalProfile.sharedInstance.printAllData()
self.animateScreen(loggedIn: LocalProfile.sharedInstance.loggedIn) //Call that doesn't work
})
}
}
public func animateScreen(loggedIn: Bool) {
if(loggedIn) {
//Animating screen objects
print("> Animating screen objects")
UIView.animate(withDuration: 0.7, delay: 1.0, options: UIViewAnimationOptions.curveEaseOut, animations: {
self.BTN_facebookLogin.frame = CGRect(x: self.BTN_facebookLogin.frame.origin.x, y: (self.view.bounds.height - self.BTN_facebookLogin.frame.size.height) - 50, width: self.BTN_facebookLogin.frame.size.width, height: self.BTN_facebookLogin.frame.size.height)
self.IMG_ProfilePicture.alpha = 1
self.LBL_Name.alpha = 1
self.view.layoutIfNeeded()
}, completion: { finished in
print("> Done animating screen objects")
})
}
else {
//Not animating
print("> Not animating screen objects")
}
}
Any help here would be appreciated! Thanks
EDIT: Below code returns that it IS the main thread...
LocalProfile.sharedInstance.updateFromFacebook(updateFromFacebook_Complete: {
self.LBL_Name.text = LocalProfile.sharedInstance.firstName
self.IMG_ProfilePicture.image = LocalProfile.sharedInstance.profilePicture
LocalProfile.sharedInstance.printAllData()
self.animateScreen(loggedIn: LocalProfile.sharedInstance.loggedIn)
let notString = Thread.isMainThread ? "" : "not "
print("This is " + notString + "the main thread")
})

Answer 1

Work around:
Try to update your buttons frame in the main queue. In swift 3.0 you can do as bellow:
DispatchQueue.main.async
{
self.BTN_facebookLogin.frame = CGRect(x: self.BTN_facebookLogin.frame.origin.x, y: (self.view.bounds.height - self.BTN_facebookLogin.frame.size.height) - 50, width: self.BTN_facebookLogin.frame.size.width, height: self.BTN_facebookLogin.frame.size.height)
self.IMG_ProfilePicture.alpha = 1
self.LBL_Name.alpha = 1
self.view.layoutIfNeeded()
}

Answer 2

As others have said, you must make UI calls from the main thread. I'm not familiar with Facebook's APIs, so I don't know if the completion block you're using is called on the main thread or not. You can check with code like this:
let notString = Thread.isMainThread ? "" : "not "
print("This is " + notString + "the main thread")
(That's Swift 3 code)
Put that at the top of your completion block and see what it displays to the console.
My bet is that the completion block is NOT being run on the main thread.
The most common effect of doing UI calls from a background thread is that nothing happens, or it takes a VERY long time to take effect. However, it can also cause other strange effects and even crashes, so it's important not to do it.
You might also be having problems with auto-layout interfering with your frame settings, but based on the symptoms you describe (not working from the completion block but working if you call it directly) it sounds more like a threading problem.
Any time you deal with a completion block you should figure out if the completion block might be called from a background thread. Apple's URLSession class is an example of a class that calls it's completion blocks on background threads. The docs should tell you if a completion block is invoked on a background thread, but the test code I posted above is a good way to be sure.
In contrast, the UIView animateWithDuarion(animations:completion:) family of methods call their completion blocks on the main thread.