swift - Updating existing constraints does not work, wrong use of .active property? -

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i have storyboard contains :

  • a "tab bar" on left 5 tabs
  • a container on right side of tab bar contains 6 image views share same space looks :

standard storyboard

each image view configured occupy 1/3 of container's width , 1/2 of height.

however, different ratios can provided @ runtime (from json file) example, 1st image view's height become 70% of container's height , 50% of width (therefore, 2nd , 3rd image views widths occupy 25% of container's width , 4th image view, 2nd line column 1 has height of 30% of image view).

to here tried :

-create 2 arrays of outlets (width , height constraints image views) :

// height constraints @iboutlet var heightconstraints: [nslayoutconstraint]!  // width constraints @iboutlet var widthconstraints: [nslayoutconstraint]!

-create outlet container of image views

// drawings - container @iboutlet weak var drawingview: uiview!

-create stored properties update constraints (these not outlets)

// drawing height property var drawingheightconstraint: nslayoutconstraint?  // drawing width property var drawingwidthconstraint: nslayoutconstraint?

and here comes job : i've overridden updateviewconstraints(), mistake ? seemed best place update constraint saw people use viewwillappear... method called every time click on tab (and load new drawings new ratios)

public override func updateviewconstraints() {     super.updateviewconstraints()      // activate default height , width constraints     papoohomepageviewcontroller.activateconstraint(constraints: heightconstraints)     papoohomepageviewcontroller.activateconstraint(constraints: widthconstraints)      // deactivate temporarily created new height , width constraints     drawingheightconstraint?.active = false     drawingwidthconstraint?.active = false      // display drawings     let drawingelements:[(string, double, double)] = papoobrain.getdrawings(forsection: currentsection)     (index, (drawing, heightratio, widthratio)) in drawingelements.enumerate() {         drawingviews[index].image = uiimage(named: drawing)          // update height constraint if ratio different defaut ratio of 1/2         if heightratio != double(heightconstraints[index].multiplier) {             heightconstraints[index].active = false             drawingheightconstraint = nslayoutconstraint(item: drawingviews[index], attribute: .height, relatedby: .equal, toitem: drawingview, attribute: .height, multiplier: cgfloat(heightratio), constant: 0)             drawingheightconstraint!.active = true         }          if widthratio != double(widthconstraints[index].multiplier) {             widthconstraints[index].active = false             drawingwidthconstraint = nslayoutconstraint(item: drawingviews[index], attribute: .width, relatedby: .equal, toitem: drawingview, attribute: .width, multiplier: cgfloat(widthratio), constant: 0)             drawingwidthconstraint!.active = true         }      }      // 1 should or should not call, in order ?     drawingview.setneedsupdateconstraints()     drawingview.setneedslayout()     drawingview.layoutifneeded() }

-here code of little helper activate constraints. note: problem. try activate constraint deactivated (it comes array of outlets) don't want duplicated

class func activateconstraint(constraints constraints: [nslayoutconstraint]) {     constraint in constraints {         constraint.active = true     } }

-finally, here piece of json see parse...

"drawings": [     {         "image": "01-01-drawing.png",             "height-ratio": "0.5",             "width-ratio": "0.33",          etc.

the problem(s)

  • if change configuration file (json) "okay, image view 1's height ratio o.7 , image view 4's height ratio 0.3" : have conflicting constraints (it seems after all, "active" property did not deactivate constraint

so when debugging, see constraints of width , height getting duplicated, causing nightmare.

  • the same happens height etc.

many questions here

  • did use correctly (in terms of lifecycle etc.) updateviewconstraints() ? call super @ beginning ?

  • what correct use of setneedslayout, layoutifneeded, setneedsupdateconstraints...

  • when set outlet nslayoutconstraint's active property false. active = true afterwards, did correct reference default height/width storyboard ?

thank reading


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