orkenstein orkenstein - 2 months ago 14
iOS Question

How to animate UITableViewCell height using auto-layout?

There are lot of similar questions on Stack Overflow about

UITableViewCell
height animation, but nothing works for new iOS8 auto-layout driven table view. My issue:

Custom cell:

@property (weak, nonatomic) IBOutlet iCarousel *carouselView;
@property (weak, nonatomic) IBOutlet UIPageControl *pageControl;
@property (weak, nonatomic) IBOutlet UIButton *seeAllButton;
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *carouselHeightConstraint;


Note
carouselHeightConstraint
. This is height constraint for content view's subview (the only subview).

Height is set to
230.0f
for example. On first load it looks like:
enter image description here

Then, on See All action I want to expand cell, my code:

- (IBAction)seeAllButtonAction:(id)sender {

BOOL vertical = !self.carouselCell.carouselView.vertical;
self.carouselCell.carouselView.type = vertical ? iCarouselTypeCylinder : iCarouselTypeLinear;
self.carouselCell.carouselView.vertical = vertical;

[UIView transitionWithView:self.carouselCell.carouselView
duration:0.2
options:0
animations:^{

self.carouselCell.carouselHeightConstraint.constant = vertical ? CGRectGetHeight(self.tableView.frame) : 230;
[self.carouselCell setNeedsUpdateConstraints];
[self.carouselCell updateConstraintsIfNeeded];
[self.tableView beginUpdates];
[self.tableView endUpdates];

completion:^(BOOL finished) {
}];
}


As you can see, I try to use this good old solution:

Can you animate a height change on a UITableViewCell when selected?

And the result:

enter image description here

My cell shrinks to
44.0f
height.

Question:



Why this happens? I expect to see my cell smoothly expanded with magic of auto-layot.

Note:

I dont't want to use
-tableView:heightForRowAtIndexPath:
. It's auto-layout era, right?

Answer

The following worked for me:

Preparation:

  1. On viewDidLoad tell the table view to use self-sizing cells:

    tableView.rowHeight = UITableViewAutomaticDimension;
    tableView.estimatedRowHeight = 44; // Some average height of your cells
    
  2. Add the constraints as you normally would, but add them to the cell's contentView!

Animate height changes:

Say you change a constraint's constant:

myConstraint.constant = newValue;

...or you add/remove constraints.

To animate this change, proceed as follows:

  1. Tell the contentView to animate the change:

    [UIView animateWithDuration: 0.3 animations: ^{ [cell.contentView layoutIfNeeded] }]; // Or self.contentView if you're doing this from your own cell subclass
    
  2. Then tell the table view to react to the height change with an animation

    [tableView beginUpdates];
    [tableView endUpdates];
    

The duration of 0.3 on the first step is what seems to be the duration UITableView uses for its animations when calling begin/endUpdates.

Bonus - change height without animation and without reloading the entire table:

If you want to do the same thing as above, but without an animation, then do this instead:

[cell.contentView layoutIfNeeded];
[UIView setAnimationsEnabled: FALSE];
[tableView beginUpdates];
[tableView endUpdates];
[UIView setAnimationsEnabled: TRUE];

Summary:

// Height changing code here:
// ...

if (animate) {
    [UIView animateWithDuration: 0.3 animations: ^{ [cell.contentView layoutIfNeeded]; }];
    [tableView beginUpdates];
    [tableView endUpdates];
}
else {
    [cell.contentView layoutIfNeeded];
    [UIView setAnimationsEnabled: FALSE];
    [tableView beginUpdates];
    [tableView endUpdates];
    [UIView setAnimationsEnabled: TRUE];
}

You can check out my implementation of a cell that expands when the user selects it here (pure Swift & pure autolayout - truly the way of the future).

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