UICollectionVIew inside a UITableViewCell how to get dynamic height with autolayout

Question

I know that there is a similar question, but I'd like to give more hints about how I tried to achieve that since the original question doesn't give any advice.
I have a UITableViewCell as a subview of the contentView there is a UICollectionView, I'd like to have the cell height in function of the collectionview contentSize, the table view cell is the collection view delegate and datasource.
The collection view should be fixed without scrolling possibilities in a vertical flow and it should adapt its height on the number of cell lines.
To do that I've tried to used the same technique I use with common table view cells. I create a fake cell and keep a reference to it, then in the method - (CGFloat) tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath I feed the cell with the data that it should display and then ask to its height for compressed size.
Something like that:

- (CGFloat) tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    CGSize  size = CGSizeZero;
    NSDictionary * data = self.data[indexPath.row];
    if (data[KEY_CELL_IDENTIFIER] == CellIdentifierPost) {
        NSNumber * cachedHeight = [self.heightCaches objectForKey:[(PostObject*)data[KEY_CELL_DATA] postObjectId]];
        if (cachedHeight) {
            return (CGFloat)[cachedHeight doubleValue];
        }
        [_heightCell configureCellWith:data[KEY_CELL_DATA]];
        size = [_heightCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
        [self.heightCaches setObject:@(size.height) forKey:[(PostObject*)data[KEY_CELL_DATA] postObjectId]];
    }
    else if (data[KEY_CELL_IDENTIFIER] == CellIdentifierComment){
        size = (CGSize) {
            .width = NSIntegerMax,
            .height = 160.f
        };
    }
    else {
        size = (CGSize) {
            .width = NSIntegerMax,
            .height = 50.f
        };
    }

    return size.height;
}

This method works really fine for the other cells, but not for this one, the result is a totally compressed cell with almost a zero height.
The problem seems to be due to the inner cells placement. Even if after feeding the data I force the collection view to reload data, it seems to never call the -collectionView:cellForItemAtIndexPath: this happens probably because the cell is still not displayed.
Is there a work around?

Answer 1

I'd recommend you to create a height constraint for your collectionView.

Then, based on the number of cells, you may calculate the height for it, and, at the end, you update that constraint and call [collectionView setNeedsUpdateConstraints]