ios - Setting initial height for constraint-animated UIView -


i want animate view (the green 1 in screenshots) it's bottom height defined proximity top layout guide. plan animate vertical distance constraint (top of green box top layout guide), so:

enter image description here enter image description here

here's code:

- (ibaction)upbutton:(uibutton *)sender {     self.animatedheightconstraint.constant = 20;     [uiview animatewithduration:0.5                      animations:^{                          [self.view layoutifneeded];                      } completion:nil]; }

fine, works.

however, scheme doesn't take account starting height of view, want small, zero. since @ point i'm relying on constant set in storyboard set starting height, constant can number, depending on device.

i need positive method set initial, device-independent starting point top of green uiview.

my first thought set height constraint, compiler detects conflict, , corrects breaking restraint.

my second thought, although seems pretty clumsy, set both constraints, remove vertical constraint @ runtime, remove height constraint , add vertical constraint.

am missing obvious, or there no more elegant way go this?

update:

since haven't received answer yet, tried implementing second thought, detailed above. added initialheightconstraint green bar via code:

-(void)viewwillappear:(bool)animated {     [self.view removeconstraint:self.animatedheightconstraint];     [self.greenbar addconstraint:self.initialheightconstraint];      self.initialheightconstraint.constant = 1;     [self.view setneedslayout];  }

this works. greenbar set desired height, different constant in soryboard:

enter image description here

next, try swap out 2 constraints , animate animatedheightconstraint:

- (ibaction)upbutton:(uibutton *)sender {     [self.greenbar removeconstraint:self.initialheightconstraint];     [self.view addconstraint:self.animatedheightconstraint];      [self.view setneedslayout];       self.animatedheightconstraint.constant = 20;      [uiview animatewithduration:0.5                      animations:^{                          [self.view layoutifneeded];                      } completion:nil]; }

this doesn't work. crashes with:

terminating app due uncaught exception 'nsinternalinconsistencyexception', reason: 'invalid parameter not satisfying: [constraint iskindofclass:[nslayoutconstraint class]]'

unfortunately, don't understand means. use help!


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