ios - UIViewAnimation assign correct value on second run -

i want animate uiview uiimageview in it. code below it's seams correct uiview.frame value animation assign in second run. have no idea why that. in second run animation want to.

code

private func animatetopreviewmode(){     let y = uiscreen.mainscreen().bounds.height * 0.2     let width = uiscreen.mainscreen().bounds.width     let height = uiscreen.mainscreen().bounds.height * 0.4     let frame = cgrectmake(0, y, width, height)     previewimageview.image = stillimage     frameforcapture.hidden = true     previewview.hidden = false     println("run")     println("target frame \(frame)")     println("preanimation\(previewview.frame)")     uiview.animatewithduration(1.5, delay: 0, usingspringwithdamping: 0.5, initialspringvelocity: 1, options: uiviewanimationoptions.beginfromcurrentstate, animations: { () -> void in         println("pre set \(self.previewview.frame)")         self.previewview.frame = frame         println("post set\(self.previewview.frame)")         }) { (complete) -> void in             //complete             //all buttons enabled         println("complete: \(self.previewview.frame)")     } } 

view hierarchy

output

target frame (0.0, 113.6, 320.0, 227.2) preanimation(0.0, 0.0, 320.0, 568.0) pre set (0.0, 0.0, 320.0, 568.0) post set(0.0, 113.6, 320.0, 227.2) complete: (0.0, 0.0, 320.0, 568.0) run target frame (0.0, 113.6, 320.0, 227.2) preanimation(0.0, 0.0, 320.0, 568.0) pre set (0.0, 0.0, 320.0, 568.0) post set(0.0, 113.6, 320.0, 227.2) complete: (0.0, 113.6, 320.0, 227.2) 

update

if turn previewimageview.image = stillimage works expected. -.-