iOS中的跳过/忽略方法

Question

How can I skip a complete method in iOS? I know how to test for the iOS version inside a method, but not how to completely ignore a method.

Concrete example: iOS8 added self sizing table view cells, and the methods heightForRowAtIndexPath: and estimatedHeightForRowAtIndexPath: are no longer required. But I do need them for iOS7. Now when I step through the code in iOS8, both methods are called, even though they are no longer needed.

Answer 1

You have a UITableViewDelegate set as the delegate for a UITableView and you want to present different delegate methods to different versions of iOS.

UITableView will call [delegate respondsToSelector:@selector(tableView:heightForRowAtIndexPath:)] before calling [delegate tableView:self heightForRowAtIndexPath:indexPath] .

This calls for a custom -respondsToSelector: . In your UITableViewDelegate class add this method.

- (BOOL)respondsToSelector:(SEL)aSelector
{
    // If this device is running iOS 8 or greater.
    if ([[[UIDevice currentDevice] systemVersion] compare:@"8.0" options:NSNumericSearch] != NSOrderedAscending) {
        if (aSelector == @selector(tableView:heightForRowAtIndexPath:))
            return NO;

        if (aSelector == @selector(tableView:estimatedHeightForRowAtIndexPath:))
            return NO;
    }

    return [super respondsToSelector:aSelector];
}

---

UPDATE: I fixed the delegate method names. DUH!

Answer 2

Provide a different delegate based on iOS version. This allows you to encapsulate your code in meaningfully-named blocks (your interface will indicate that it's iOS7) and you won't be doing any trickery with respondsToSelector that could break subclasses of your class that actually do want to use those methods.

@interface MyTableViewDelegate : NSObject <UITableViewDelegate>
@end

@interface MyTableViewDelegateiOS7 : MyTableViewDelegate
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath;
- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath;
@end

@implementation YourClass : .. <..>
// ..
- (void)loadView {
  [super loadView];
  if ([[[UIDevice currentDevice] systemVersion] compare:@"8.0" options:NSNumericSearch] != NSOrderedAscending) {
    self.tableView.delegate = [[MyTableViewDelegate alloc] init];
  } else {
    self.tableView.delegate = [[MyTableViewDelegateiOS7 alloc] init];
  }
}
@end