ios - uiscrollview's autolayout,The view hierarchy is not prepared for the constraint -

i want add scrolling imageviews scrollviews using autolayout.

the view hierarchy folllows:

---|

|---placeholder view

|---scroll view

the code follows:

-(uicollectionviewcell*)collectionview:(uicollectionview *)collectionview cellforitematindexpath:(nsindexpath *)indexpath {

static nsstring* identifier = @"wcollectionviewcell";   wcollectionviewcell* cell =[collectionview dequeuereusablecellwithreuseidentifier:identifier forindexpath:indexpath]; cell.imagescrollview.backgroundcolor=[uicolor orangecolor];  uiimageview* imageview1 = [[uiimageview alloc]init]; imageview1.image =[uiimage imagenamed:@"1.jpg"]; imageview1.translatesautoresizingmaskintoconstraints=no; [cell.imagescrollview addsubview:imageview1];  nsdictionary* views = @{@"imageview1":imageview1,@"placeview":cell.placeholderview,@"scrollview":cell.imagescrollview};  //set imageview'size nsarray *img_constraint_h = [nslayoutconstraint constraintswithvisualformat:@"v:[imageview1(placeview)]"                                                                     options:0                                                                     metrics:nil                                                                       views:views];  nsarray *img_constraint_v = [nslayoutconstraint constraintswithvisualformat:@"h:[imageview1(placeview)]"                                                                     options:0                                                                     metrics:nil                                                                       views:views];  [self.view addconstraints:img_constraint_h]; [self.view addconstraints:img_constraint_v];   //set imageview's position nsarray*  top_position = [nslayoutconstraint constraintswithvisualformat:@"h:|-0-[imageview1]"                                                             options:0 metrics:nil views:views];  nsarray* bottom_position = [nslayoutconstraint constraintswithvisualformat:@"v:|-0-[imageview1]"                                                               options:0 metrics:nil views:views];  [cell.imagescrollview addconstraints:top_position]; [cell.imagescrollview addconstraints:bottom_position];  return cell; 

}

--------error---------- 2015-04-10 12:20:46.245 t[92361:1319616] view hierarchy not prepared constraint: 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 _viewhierarchyunpreparedforconstraint:] debug. 2015-04-10 12:20:46.246 t[92361:1319616] * assertion failure in -[uiview _layoutengine_didaddlayoutconstraint:roundingadjustment:mutuallyexclusiveconstraints:], /sourcecache/uikit_sim/uikit-3318.93/nslayoutconstraint_uikitadditions.m:560 2015-04-10 12:20:46.249 t[92361:1319616] * terminating app due uncaught exception 'nsinternalinconsistencyexception', reason: 'impossible set layout view hierarchy unprepared constraint.'

your problem adding constraints height , width of image self.view not parent view of image.

you need add constraints cell.imagescrollview, cell superview or image itself.

so both of should work:

//set imageview'size nsarray *img_constraint_h = [nslayoutconstraint constraintswithvisualformat:@"v:[imageview1(placeview)]"                                                                     options:0                                                                     metrics:nil                                                                       views:views];  nsarray *img_constraint_v = [nslayoutconstraint constraintswithvisualformat:@"h:[imageview1(placeview)]"                                                                     options:0                                                                     metrics:nil                                                                       views:views];  [cell.imagescrollview addconstraints:img_constraint_h]; [cell.imagescrollview addconstraints:img_constraint_v]; 

or

[imageview1 addconstraints:img_constraint_h]; [imageview1 addconstraints:img_constraint_v]; 

you have both options because constraints don't reference parent, imageview. if there | in visual format, first option work.

one more tip:

you add constraints @ once:

wcollectionviewcell* cell =[collectionview dequeuereusablecellwithreuseidentifier:identifier forindexpath:indexpath]; cell.imagescrollview.backgroundcolor=[uicolor orangecolor];  uiimageview* imageview1 = [[uiimageview alloc]init]; imageview1.image =[uiimage imagenamed:@"1.jpg"]; imageview1.translatesautoresizingmaskintoconstraints=no; [cell.imagescrollview addsubview:imageview1];  nsdictionary* views = @{@"imageview1":imageview1,@"placeview":cell.placeholderview,@"scrollview":cell.imagescrollview};     //set imageview's position nsarray*  horizontal_constraints = [nslayoutconstraint constraintswithvisualformat:@"h:|-0-[imageview1(placeview)]"                                                             options:0 metrics:nil views:views];  nsarray* vertical_constraints = [nslayoutconstraint constraintswithvisualformat:@"v:|-0-[imageview1(placeview)]"                                                               options:0 metrics:nil views:views];  [cell.imagescrollview addconstraints:horizontal_constraints]; [cell.imagescrollview addconstraints:vertical_constraints];  return cell; 

let me know how goes, or if need more help!