ios - Setting up this UI with Auto Layout -

i'm trying set view auto layout animates nicely when view changes size...

the scenario is...

i have uiview subview called animview. animview starts outside of frame of view. view grows (gets taller), animview moves down @ same rate. when animview 10 points top of view (i.e. @"v:|-10-[animview]" ) stops , "sticks" point.

i.e. this...

this works (dropbox share project):

the trick use invisible uiview spacer object. view call animview set this. because set partially in ib, still raises few issues, see works want.

@implementation animview {      uiview * _innerbox;     uiview * _spacer; } 

then call method - setupeverything initwithcoder: or initwithframe:.

- (void) setupeverything {       // because set in ib autolayout off, think      // still needs this. won't work without     self.translatesautoresizingmaskintoconstraints = yes;      // otherwise see box outside of animview     self.clipstobounds = yes;      _innerbox = [[uiview alloc] init];     _innerbox.backgroundcolor = [uicolor blackcolor];     _spacer = [[uiview alloc] init];     _spacer.backgroundcolor = [uicolor clearcolor];      _innerbox.translatesautoresizingmaskintoconstraints = no;     _spacer.translatesautoresizingmaskintoconstraints = no;     [self addsubview:_innerbox];     [self addsubview:_spacer];      // give _innerbox , _spacer dimensions prevent ambiguity      nslayoutconstraint *i02 = [nslayoutconstraint constraintwithitem:_innerbox attribute:nslayoutattributewidth relatedby:nslayoutrelationequal toitem:nil attribute:0 multiplier:1.0f constant:50.0f];     nslayoutconstraint *i03 = [nslayoutconstraint constraintwithitem:_innerbox attribute:nslayoutattributeheight relatedby:nslayoutrelationequal toitem:nil attribute:0 multiplier:1.0f constant:50.0f];     nslayoutconstraint *s02 = [nslayoutconstraint constraintwithitem:_spacer attribute:nslayoutattributewidth relatedby:nslayoutrelationequal toitem:nil attribute:0 multiplier:1.0f constant:50.0f];      // center both views     nslayoutconstraint *i05 = [nslayoutconstraint constraintwithitem:_innerbox attribute:nslayoutattributecenterx relatedby:nslayoutrelationequal toitem:self attribute:nslayoutattributecenterx multiplier:1.0f constant:0.0f];     nslayoutconstraint *s04 = [nslayoutconstraint constraintwithitem:_spacer attribute:nslayoutattributecenterx relatedby:nslayoutrelationequal toitem:self attribute:nslayoutattributecenterx multiplier:1.0f constant:0.0f];      // set top of _innerbox 10.0 points top of superview low priority     nslayoutconstraint *i01 = [nslayoutconstraint constraintwithitem:_innerbox attribute:nslayoutattributetop relatedby:nslayoutrelationequal toitem:self attribute:nslayoutattributetop multiplier:1.0f constant:10.0f];     i01.priority = 250;      // pin spacer bottom of _innerbox;     nslayoutconstraint *i04 = [nslayoutconstraint constraintwithitem:_innerbox attribute:nslayoutattributebottom relatedby:nslayoutrelationequal toitem:_spacer attribute:nslayoutattributetop multiplier:1.0f constant:0.0f];      // pin spacer's bottom bottom of superview     nslayoutconstraint *s01 = [nslayoutconstraint constraintwithitem:_spacer attribute:nslayoutattributebottom relatedby:nslayoutrelationequal toitem:self attribute:nslayoutattributebottom multiplier:1.0f constant:0.0f];      // stretch spacer out needed     nslayoutconstraint *s03 = [nslayoutconstraint constraintwithitem:_spacer attribute:nslayoutattributeheight relatedby:nslayoutrelationgreaterthanorequal toitem:nil attribute:0 multiplier:1.0f constant:80.0f];       [self addconstraints:@[i01,i02,i03,i04,i05,s01,s02,s03,s04]];  }