我最终解决了这个问题，如果其他人有更优雅的解决方案，请告诉我：

I ended up solving my problem like this, and if someone else has a more elegant solution please let me know:

- (void)viewDidLoad {

    [super viewDidLoad];

    UIMenuItem *highlightMenuItem = [[UIMenuItem alloc] initWithTitle:@"Highlight" action:@selector(highlight)];
    [[UIMenuController sharedMenuController] setMenuItems:[NSArray arrayWithObject:highlightMenuItem]];

    float sysVer = [[[UIDevice currentDevice] systemVersion] floatValue];

    if (sysVer >= 8.0) {
        self.textView.layoutManager.allowsNonContiguousLayout = NO;
    } 
}

- (void)highlight {

    NSRange selectedTextRange = self.textView.selectedRange;

    [attributedString addAttribute:NSBackgroundColorAttributeName
                             value:[UIColor redColor]
                             range:selectedTextRange];

    float sysVer = [[[UIDevice currentDevice] systemVersion] floatValue];
    if (sysVer < 8.0) {
        // iOS 7 fix
        self.textView.scrollEnabled = NO;
        self.textView.attributedText = attributedString;
        self.textView.scrollEnabled = YES;
    } else {
        self.textView.attributedText = attributedString;
    }
}