Frames changing suddenly instead of animating [iOS]
<p>I have a view with a scroll view in my app (a percentage calculator). I am trying to animate the view to fly out and then fly in again from the left albeit with different contents, on the press of a button.
Here's my code:</p>

<pre><code>func next()
{
    UIView.animateWithDuration(0.5, animations: {
        self.mainView.frame = CGRectMake(-500, self.view.bounds.height/2-self.mainHeight/2, self.mainWidth, self.mainHeight)
        self.mainView.center.x -= 600
    }) { (success) in
        self.mainView.center.x += 1200    
    }

    UIView.animateWithDuration(0.5, animations: {
        self.mainView.frame = CGRectMake(self.view.bounds.width/2-self.mainWidth/2, self.view.bounds.height/2-self.mainHeight/2, self.mainWidth, self.mainHeight)
    }) { (success) in
        print("Animation Successful!")
        self.drawView()
    }
}
</code></pre>

<p>I don't understand why, but the animation doesn't occur, the view disappears completely and I see <code>"Animation Successful"</code> in the logs.
To be clear, I have created the view programmatically.</p>

<p>Here's the code in viewDidLoad(); the view displays correctly when it's called:</p>

<pre><code>    mainHeight = self.view.bounds.height * 0.85
    mainWidth = self.view.bounds.width * 0.85
    let viewHeight = self.view.bounds.height
    let viewWidth = self.view.bounds.width

    mainView.frame = CGRectMake(viewWidth/2-mainWidth/2, viewHeight/2-mainHeight/2, mainWidth, mainHeight)
    mainView.layer.cornerRadius = 8
    mainView.layer.masksToBounds = true
    mainView.backgroundColor = getColor(0, green: 179, blue: 164)
    self.view.addSubview(mainView)

    scrollView.frame = CGRectMake(0, 0, mainWidth, mainHeight)
    scrollView.contentSize = CGSizeMake(mainWidth, 800)
    self.mainView.addSubview(scrollView)

    contentView.frame = CGRectMake(0, 0, mainWidth, 800);
    contentView.backgroundColor = getColor(0, green: 179, blue: 164)
    contentView.layer.masksToBounds = true
    contentView.clipsToBounds = true
    self.scrollView.addSubview(contentView)
</code></pre>