iOS 7和iOS 8中的动态单元格高度-我只能在iOS 7中支持heightForRowAtIndexPath吗？

Question

I have a table view with dynamically sized cells. This works great in iOS 8 but it's not supported in iOS 7. I'm required to implement tableView:heightForRowAtIndexPath or the app will crash in iOS 7. If I do that, I'm going to have to calculate the height of the cell. The problem is that if I implement this method, iOS 8 pays attention to it and no longer does its dynamically sized cell magic. Is there any way to only implement this method for iOS 7 clients?

Answer 1

I have used something similar to this before:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [self dequeueReusableCellWithIdentifier:@"CellIdentifier"];

    // Stuff & Things

    [cell.contentView setNeedsLayout];
    [cell.contentView layoutIfNeeded];

    return [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
}

Answer 2

The new internal autolayout self-sizing cells from iOS 8 cannot magically be reflected back to iOS 7. But that's not a problem. If you want to be backwards-compatible to iOS 7, then, as you rightly say, this means that you will determine the cell height yourself, so that you can return the correct value from tableView:heightForRowAtIndexPath: . This is what we did in iOS 4, 5, 6, and 7. That will still work in iOS 8 too (and is probably faster anyway).

So my advice would be: just write the code as if for iOS 7. If you're coding in Objective-C you could have two different sets of code (conditional compilation), and even in Swift you could use two different classes, depending on what system we find ourselves on; but I regard that as a bit over the top - it's a code maintenance nightmare waiting to happen.

Answer 3

I got UIViewAlertForUnsatisfiableConstraints error in debug log.

Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) ( "", "", "" )

If there is no tableView:heightForRowAtIndexPath: , the cell looks fine. So, I want to disable it in iOS 8. @batu gave a solution in another post: Implement heightForRowIndexPath: in iOS 7, but remove it in iOS 8 using compile-time macro . Thanks to @batu, the solution is as simple as this:

#define IS_IOS_8_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)

-(CGFloat) tableView: (UITableView * ) tableView heightForRowAtIndexPath: (NSIndexPath * ) indexPath {
  if (IS_IOS_8_OR_LATER) {
    return UITableViewAutomaticDimension;
  }
  // Your iOS 7 code here.
}

However , my cell still has problem with the height in iOS 8 with iPhone 6. The causes seems to be the fixed width of UILabel (which is designed for 320pt). Here is what I did after a long night research:

1. I applied the solution from this guide: Dynamic Table View Cell Height and Auto Layout .

2. Since the UILabel requires explicit width for iOS 7 device, I programmatically "clear" this settings for iOS 8. In my extended table view cell:

    - (void)awakeFromNib { // Initialization code if (IS_IOS_8_OR_LATER) { self.descriptionLabel.preferredMaxLayoutWidth = 0; } } 

3. I used the RWLabel suggestion as from the guide.

4. I disable return UITableViewAutomaticDimension; . Whether enable or disable, may depends on the subviews and constraints in table view cell. Try to fit your case.

5. I change the priority of the Trailing Space for all RWLabel to 999 (instead of 1000). That eliminates the unsatisfiable constraints warning.

Hopefully these solutions would help someone.