iOS8 - constraints ambiguously suggest a height of zero

What can also be done is adding vertical constraints from the top and to the bottom of the content view. This will make autolayout happy (because he now knows how to calculate the height of the cell himself).

Forcing a return height and estimated height made the warning disappear in my case.

- (CGFloat)tableView:(UITableView *)tableView 
           estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 44;
}

- (CGFloat)tableView:(UITableView *)tableView 
           heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 44;
}

Another solution where you don't need the two overrides is simply to use self.tableView.rowHeight = 44; in your loadView or init method.