Swift中来自目标C的完成块

Question

I'm having trouble translating this over to Swift. Any help is GREATLY appreciated, thank you!

[segControl setTitleFormatter:^NSAttributedString *(LBCSegmentedControl *segmentedControl, NSString *title, NSUInteger index, BOOL selected) {
         NSAttributedString *attString = [[NSAttributedString alloc] initWithString:title attributes:@{NSForegroundColorAttributeName : [UIColor blueColor]}];
         return attString;
         }];

Answer 1

You only use title in the block so may as well replace the other 3 parameters with _ , meaning you don't care about them. Give this a try:

segControl.tittleFormater = {_, title, _, _ -> NSAttributedString in
    NSAttributedString(string: title, attributes:[
        NSForegroundColorAttributeName: UIColor.blueColor
    ])
}

Or a longer version, if the compiler complains about ambigous data types:

segControl.tittleFormater = {(segmentedControl: LBCSegmentedControl, title: NSString, index: Int, selected: Bool) -> NSAttributedString in
    NSAttributedString(string: title, attributes:[
        NSForegroundColorAttributeName: UIColor.blueColor
    ])
}

Answer 2

It depends upon how the setTitleFormatter was implemented. If it's just a method, you'd do something like:

segControl.setTitleFormatter { (segmentedControl, title, index, selected) -> NSAttributedString! in
    return NSAttributedString(string: title, attributes: [NSForegroundColorAttributeName : UIColor.blueColor()])
}

If it was defined as a block property, you'd do something like:

segControl.titleFormatter = { (segmentedControl, title, index, selected) -> NSAttributedString! in
    return NSAttributedString(string: title, attributes: [NSForegroundColorAttributeName : UIColor.blueColor()])
}

Both of the above assume the Objective-C class lacks nullability annotations. If it has been audited for nullability, then some of those ! will either be ? or not needed at all.