Autolayout Constraint - Keyboard

Question

Im stuck trying to animate a table view smoothly which has an autolayout contraint. I have a reference to the constraint "keyboardHeight" in my .h and have linked this up in IB. All i want to do is animate the table view with the keyboard when it pops up. Here is my code:

- (void)keyboardWillShow:(NSNotification *)notification
{
    NSDictionary *info = [notification userInfo];
    NSValue *kbFrame = [info objectForKey:UIKeyboardFrameEndUserInfoKey];
    NSTimeInterval animationDuration = [[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    CGRect keyboardFrame = [kbFrame CGRectValue];
    CGFloat height = keyboardFrame.size.height;

    [UIView animateWithDuration:animationDuration animations:^{
        self.keyboardHeight.constant = -height;
        [self.view setNeedsLayout];
    }];
}

The thing is the animation block is instantaneous and I see white space appear before the keyboard has finished its animation. So basically I see the white background of the view as the keyboard is animating. I cannot make the animation last for as long as the keyboard is animating.

Am i approaching this the wrong way? Thanks in advance!

Answer 1

Try it this way:

self.keyboardHeight.constant = -height;
[self.view setNeedsUpdateConstraints];

[UIView animateWithDuration:animationDuration animations:^{
   [self.view layoutIfNeeded];
}];

Remember this pattern because this should be the correct way to update constraint-based layouts (according to WWDC). You can also add or remove NSLayoutConstraints as long as you call setNeedsUpdateConstraints after.