ios - How to animate a UIView that has constraints? -

i have 2 uiviews animate on screen , off. both should start positioned off screen. top animates downward, bottom upward. without constraints works expected. with, uiviews visible @ app launch (with slight animation visible). animate off screen though.

for top uiview, have leading space, trailing space, top space, , height.

for bottom uiview, have leading space, trailing space, bottom space, , height.

how should adjust code and/or constraints desired animation?

here code:

- (void)viewdidload {     [super viewdidload];     // additional setup after loading view, typically nib. }  - (void)viewdidappear:(bool)animated {     [super viewdidappear:animated];     [self animateviewsin]; }  - (void)viewwilllayoutsubviews {     [super viewwilllayoutsubviews];      self.topview.frame = cgrectmake(16.0, -self.topview.frame.size.height, self.topview.frame.size.width, self.topview.frame.size.height);      self.bottomview.frame = cgrectmake(16.0, self.view.bounds.size.height, self.bottomview.frame.size.width, self.bottomview.frame.size.height); }  - (void)didreceivememorywarning {     [super didreceivememorywarning];     // dispose of resources can recreated. }  - (void)animateviewsin {     [uiview animatewithduration:0.5                       delay:1.0                     options: uiviewanimationoptioncurveeasein                  animations:^{                      self.topview.frame = cgrectmake(16.0,      self.topview.frame.size.height/8.0, self.topview.frame.size.width,      self.topview.frame.size.height);                      self.bottomview.frame = cgrectmake(16.0, (self.view.bounds.size.height-self.bottomview.frame.size.height)-20.0, self.bottomview.frame.size.width, self.bottomview.frame.size.height);                  }                  completion:^(bool finished){                      nslog(@"done!");                  }]; }  - (ibaction)animateviewsout:(id)sender {     cgrect baskettopframe = self.topview.frame;     baskettopframe.origin.y = -baskettopframe.size.height;      cgrect basketbottomframe = self.bottomview.frame;     basketbottomframe.origin.y = self.view.bounds.size.height;       [uiview animatewithduration:0.5                       delay:1.0                     options: uiviewanimationoptioncurveeaseout                  animations:^{                      [self.view layoutifneeded];                       self.topview.frame = baskettopframe;                      self.bottomview.frame = basketbottomframe;                  }                  completion:^(bool finished){                      nslog(@"done!");                  }]; } 

when using constraints, should not adjusting frames. should modifying constant property of constraint (or deactivinging 1 constraint , activating another).

here's example of animating top view in top, assuming added @iboutlet called topconstraint top constraint of view topview:

in objective-c:

- (void)viewdidappear:(bool)animated {     [super viewdidappear:animated];      self.topconstraint.constant = -self.topview.frame.size.height;  // or whatever want     [self.view layoutifneeded];     [uiview animatewithduration:0.5 delay:1 options:0 animations:^{         self.topconstraint.constant = 0;         [self.topview layoutifneeded];     } completion:nil]; } 

in swift:

override func viewdidappear(_ animated: bool) {     topconstraint.constant = -topview.frame.height  // or whatever want     view.layoutifneeded()     uiview.animate(withduration: 0.5, delay: 1, animations: {         topconstraint.constant = 0         self.view.layoutifneeded()     }) }