iOS Constraints do not update quickly enough during animation

Question

I have a footer UIView at the bottom of my iOS Screen about 50 pixels high. During the loading phase of this view, I add a subview (lets say footer-subview), and programmatically add constraints to all edges with a constant of 0 (basically covering the entire footer view).

I register for the keyboardWillShow notification and within it I change the constraint to my footer view (not to be confused with the constraints mentioned in the previous paragraph), this is just one constraint that controls the outer-footer-views position) so that it shows right above the keyboard. Theoretically changing this constraint should change all related constraints along with it, specifically the outer edge constraints of my footer-subview.

When the keyboard shows, the footer view animates well with the animation of the showing keyboard, but there is a slight delay for the constraints of my footer-subview inside the footer view to update, which gives an unsightly visual effect where my footer is blank for a split second.

Here is the code for my keyboardWillShowNotifcation

- (void)keyboardWillShow:(NSNotification *)notification
{
  _keyboardIsVisible = YES;
  CGRect keyboardSize;
  [[[notification userInfo] objectForKey:UIKeyboardFrameEndUserInfoKey] getValue:&keyboardSize];
  [UIView animateWithDuration:0.35f
                        delay:0
                      options:UIViewAnimationCurveLinear | UIViewAnimationOptionBeginFromCurrentState
                   animations:^{
                     [_footerTopSpaceConstraint setConstant:-1 * CGRectGetHeight(keyboardSize)];

                     [self.view layoutIfNeeded];
                   }
                   completion:nil];

}

Any tips on how to get the footer-subview constraints updated "quicker" so that they animate well with its parent, the footer view?

nrj nrj · Accepted Answer · 2013-09-13T20:31:29

Don't be afraid to call setFrame:

- (void)keyboardWillShow:(NSNotification *)notification
{
    _keyboardIsVisible = YES;
    CGRect keyboardSize;
    [[[notification userInfo] objectForKey:UIKeyboardFrameEndUserInfoKey] getValue:&keyboardSize];
    [UIView animateWithDuration:0.35f
                          delay:0
                        options:UIViewAnimationCurveLinear|UIViewAnimationOptionBeginFromCurrentState
                     animations:^{

                         CGRect footerRect = [_myFooterView frame];
                         [_myFooterView setFrame:CGRectOffset(footerRect, 0, -CGRectGetHeight(keyboardSize))];
                     }
                     completion:^(BOOL finished) {

                         [_footerTopSpaceConstraint setConstant:-1 * CGRectGetHeight(keyboardSize)];
                         [self.view setNeedsUpdateConstraints];
                     }];
}

iOS Constraints do not update quickly enough during animation

1 Answers