Load custom UITableViewCell from Storyboard

Question

Currently I'm using auto layout with storyboard to dynamically resize custom UITableViewCell's. Everything is working as it should except there is memory leak when scrolling.

I know the problem is from calling

[self.tableView dequeueReusableCellWithIdentifier:CellIdentifier];

from inside

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath

My question is this, what would be the best way to create a reference cell? How to load a cell from storyboard without dequeueReusableCellWithIdentifier?

And is it ok to maybe call dequeueReusableCellWithIdentifier from viewDidLoad and create a reference cell as a property?

I need reference cell for sizing purposes.

Thanks for any help.

score 10 · Accepted Answer · edited May 23 '17 at 12:25

Regarding how to create reference cell (see original question), there are couple of options as I can see:

create a custom cell with XIB, great article here -> a link!
- this was pointed out to me by @smileyborg, thanks!
create your custom cell in code, along with constraints.
create your custom cell in storyboard as prototype cell
- after that there are 2 options:
  - drag and drop custom cell from table view to the storyboard scene, as a top level nib object (not part of the view hierarchy), and simply create outlet to it.
  - copy custom cell and paste it to the storyboard scene. When using it this way, there is no need to register original cell with table for dequeue.
  - minor problem with both approaches is that once you drag and drop custom cell to the storyboard scene, you will not be able to see it visually and arrange UI.
- great article here -> a link!

Thanks everyone for help!

score 1 · Answer 2 · answered Apr 06 '14 at 20:59

1

And is it ok to maybe call dequeueReusableCellWithIdentifier from viewDidLoad and create a reference cell as a property?

Yes, you can do this. Or lazy initialize the property:

- (UITableViewCell *)referenceCell
{
    if (!_referenceCell) {
        _referenceCell = [self.tableView dequeueReusableCellWithIdentifier:@"Cell"];
    }
    return _referenceCell;
}

answered Apr 06 '14 at 20:59

Timothy Moose

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It seems that this also will create leaks. I'm testing it right now. – Iki Apr 07 '14 at 07:52
Last night, I had an conversation with Tyler Fox (@smileyborg), he has created a great example for auto layout and dynamic table view height [link](http://stackoverflow.com/questions/18746929/using-auto-layout-in-uitableview-for-dynamic-cell-layouts-variable-row-heights/18746930#18746930), and he also confirmed that using dequeueReusableCellWithIdentifier outside of cellForRowAtIndexPath will probably create leaks. – Iki Apr 07 '14 at 07:57
Curious why @smileyborg thinks this will leak. My [TLIndexPathTools](https://github.com/wtmoose/TLIndexPathTools) uses this method to automatically calculate cell height nobody has ever reported a leak. And I just tested it. If you've got a scenario where it leaks, I'd like to take a look. – Timothy Moose Apr 07 '14 at 14:35
@TimothyMoose It's true that cells will leak when dequeued and not returned in cellForRowAtIndexPath. See discussion of this here: https://github.com/caoimghgin/TableViewCellWithAutoLayout/issues/16 Note that this probably isn't an issue if you're only calling it once and then storing the one cell for later use. But if you did this a number of times (or perhaps your view controller is created & destroyed frequently), you will see each of these cells hangs around with a retain count of 1 and thus is never deallocated. – smileyborg Apr 08 '14 at 05:28
@smileyborg Yep, I'm only dequeuing one per cell ID and reusing it. I keep them in a dictionary and they get dequeued properly along with the view controller. Since this is being done outside of the regular cell reuse cycle, I wouldn't expect them to be discarded from the reuse pool. Thanks for clarifying what you meant. – Timothy Moose Apr 08 '14 at 06:34
@smileyborg had a conversation with an apple engineer, he said that "That same method returns an autoreleased object, and in principle should not cause a memory leak." – Iki Apr 08 '14 at 07:00
@smileyborg but of course I agree with you about the leak, and it's very noticeable on my end because of frequent alloc/dealloc. It's probably a bug on their end. – Iki Apr 08 '14 at 07:24

score 0 · Answer 3 · answered Apr 06 '14 at 20:57

You can just dequeue the cell once and store the height:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSNumber *height;

    if (!height) 
    {
        UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"YourCustomCell"];
        height = @(cell.bounds.size.height);
    }

    return [height floatValue];
}

Load custom UITableViewCell from Storyboard

3 Answers3

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