How to only override a method depending on the run

问题:

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?

回答1:

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.

回答2:

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