swift - Getting run time error when adding constraints -

i'm trying center image view i'm getting error..this code:

let markerimage = #imageliteral(resourcename: "ic_new_mark_icon")      let size = cgsize(width: 60, height: 60)      var newimage = imagewithimage(image: markerimage, scaledtosize: size)      var imageview = uiimageview(image: newimage)      self.view.addsubview(imageview)       let xconstraint = nslayoutconstraint(item: imageview, attribute: .centerx, relatedby: .equal, toitem: self.view, attribute: .centerx, multiplier: 1, constant: 0)      let yconstraint = nslayoutconstraint(item: imageview, attribute: .centery, relatedby: .equal, toitem: self.view, attribute: .centery, multiplier: 1, constant: 0)      imageview.addconstraint(xconstraint)     imageview.addconstraint(yconstraint) 

and error is

2016-12-22 16:29:11.305417 googlemappractice[21426:362773] [layoutconstraints] view hierarchy not prepared constraint: <nslayoutconstraint:0x600000285f00 uiimageview:0x7ff772f15560.centerx == uiview:0x7ff772c0bd30.centerx   (inactive)>     when added view, constraint's items must descendants of view (or view itself). crash if constraint needs resolved before view hierarchy assembled. break on -[uiview(uiconstraintbasedlayout)  

the constraints need added earliest common ancestor of 2 views affected constraint. in case, self.view earlier in hierarchy constraints should added instead of imageview.

since ios 8, there easier way. once you've added view view hierarchy (with addsubview), can activate constraints instead of adding them views.

you can setting isactive property true:

xconstraint.isactive = true yconstraint.isactive = true 

or using activate class function of nslayoutconstraint active multiple constraints:

nslayoutconstraint.activate([xconstraint, yconstraint]) 

---

as mentioned @dfd in comments, should set flag:

imageview.translatesautoresizingmaskintoconstraints = false 

this tells ios not create constraints imageview based upon frame. if don't this, you'll end conflicting constraints.

you going need width , height constraints imageview well, because you've specified position far.