How to only override a method depending on the runtime system iOS version?

Question

I've implemented automatic dynamic tableview cell heights for iOS 8 by using

self.tableView.rowHeight = UITableViewAutomaticDimension;

For pre-iOS 8, which does not support automatic dynamic cell heights, I overrided the heightForRowAtIndexPath method.

This is a similar to what I did: Using Auto Layout in UITableView for dynamic cell layouts & variable row heights

The problem is to how to write code that uses automatic cell height for iOS 8 but overrides heightForRowAtIndexPath for earlier iOS versions. I'd like my custom heightForRowAtIndexPath method only if iOS version is less than 8. Any suggestions on how to do this?

You might also consider just using a different data source in iOS 7 and iOS 8. (i.e. an object of a different class) — Jesse Rusak, Sep 24 '14 at 17:07
@JesseRusak is absolutely correct, and this is the recommended practice. Create a class cluster for your data source which provides the appropriate concrete implementation at runtime. — quellish, Jan 15 '15 at 02:42

score 19 · Accepted Answer · edited Nov 26 '14 at 12:38

19

One solution would be to override the respondsToSelector: method in your view controller. Have it return NO under iOS 8 when checking for the heightForRowAtIndexPath: method.

- (BOOL)respondsToSelector:(SEL)selector {
    static BOOL useSelector;
    static dispatch_once_t predicate = 0;
    dispatch_once(&predicate, ^{
        useSelector = [[UIDevice currentDevice].systemVersion floatValue] < 8.0 ? YES : NO;
    });

    if (selector == @selector(tableView:heightForRowAtIndexPath:)) {
        return useSelector;
    }

    return [super respondsToSelector:selector];
}

This way, when the table view make a call like:

if ([self.delegate respondsToSelector:@selector(tableView:heightForRowAtIndexPath:)]) {
}

your code will return NO under iOS 8 or later and YES under iOS 7 or earlier.

edited Nov 26 '14 at 12:38

mluisbrown

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answered Sep 24 '14 at 16:43

rmaddy

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I added this as a category for `UITableViewController`, so you don't have to add it to every single one. Also you can test if the selector is `tableView:estimatedHeightForRowAtIndexPath:`, since I believe that is also not needed for iOS8. – koen Sep 28 '14 at 17:15
@Koen It's dangerous to override a method in a category since that is undefined behavior. It may work or it may not. – rmaddy Sep 28 '14 at 17:18
Good point, I will remove the category and add this to every `UITableViewController` – koen Sep 28 '14 at 17:39
2

@Koen A better solution is to create your own subclass of `UITableViewController` and add the method there. That have all of your table view controller extend your custom class. – rmaddy Sep 28 '14 at 17:40

score 1 · Answer 2 · edited Oct 20 '14 at 18:00

1

I found a simple solution. Declared this macro to recognize if user has iOS 8.0 or later:

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

Then, inside heightForRowAtIndexPath I added the following code:

if (IS_IOS_8_OR_LATER) {
        self.tableView.rowHeight = UITableViewAutomaticDimension;
        return self.tableView.rowHeight;
    } else {//Custom code for ios version earlier than 8.0

}

This solved the problem

edited Oct 20 '14 at 18:00

rmaddy

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answered Sep 24 '14 at 16:56

amirfl

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The downside to this approach is you lose a lot of the performance gain. Since the table sees that you implement the `heightForRowAtIndexPath` delegate method, it calls it for every row. My solution gives you back the performance gain. – rmaddy Sep 24 '14 at 16:58

How to only override a method depending on the runtime system iOS version?

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