自定义TableViewCell类无法返回枚举值而不会崩溃

Question

In the class that inherits my UITableViewController I have:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        var cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as GoalTableViewCell

        cell.priority = goalsArray[indexPath.row].priority as Priority //this causes no problems.
        println(cell.priority.toRaw()) //the getter causes a crash.
        //println(goalsArray[indexPath.row].priority.toRaw()) this Does Work.
        return cell
    }

In the class that is GoalTableViewCell I have:

var priority : Priority {
        get {
            if (self.priority == Priority.highPriority) {
                return Priority.highPriority
            } else if (self.priority == Priority.mediumPriority) {
                return Priority.mediumPriority
            } else if (self.priority == Priority.lowPriority) {
                return Priority.lowPriority
            } else {
                return Priority.defaultPriority
            }
        }

        set  {
            if (newValue == Priority.defaultPriority) {
                //action here.
            } else if (newValue == Priority.lowPriority) {
                //action here.
            } else if (newValue == Priority.mediumPriority) {
                //action here.
            } else if (newValue == Priority.highPriority) {
                //action here.
            }
        }
    }

The getter is not working, as the setter appears to execute fine.

The error I receive is the following:

"THREAD 1: EXC_BAD_ACCESS (code=2, address=0x7fff518d9ff8)" There is no text in the console window generated by this error and the application completely crashes and cannot continue execution beyond this point.

The line it crashes at is if (self.priority == Priority.highPriority) {

I think I am misunderstanding something about the getter?

Also here is the enum:

enum Priority : Int {
    case defaultPriority = 0
    case lowPriority = 1
    case mediumPriority = 2
    case highPriority = 3
}

Edit: Actually I cannot confirm whether the setter is working properly either, as it incorrectly performs for my tableView. if I run

    set  {
        if (newValue == Priority.defaultPriority) {
            self.backgroundColor = UIColor.redColor
        } else if (newValue == Priority.lowPriority) {
            //action here.
        } else if (newValue == Priority.mediumPriority) {
            //action here.
        } else if (newValue == Priority.highPriority) {
            //action here.
        }
    }
}

It actually incorrectly displays the cells consistently and sometimes they all become red when that should not be the case (as I scroll). I am still trying to determine what is wrong.

Answer 1

You're crashing because you've got an infinite loop in your getter. Swift does not automatically create an ivar for your computed properties like Objective-C did. So, when you call self.priority here:

var priority : Priority {
        get {
            if (self.priority == Priority.highPriority) {

you're actually just calling your getter again.

You can easily solve this by simply creating your own ivar and using it in your getting/setter:

private var _priority: Priority = Priority.defaultPriority
var priority : Priority {
    get {
        if (_priority == Priority.highPriority) {
            return Priority.highPriority
        } else if (_priority == Priority.mediumPriority) {
            return Priority.mediumPriority
        } else if (_priority == Priority.lowPriority) {
            return Priority.lowPriority
        } else {
            return Priority.defaultPriority
        }
    }

    set  {
        _priority = newValue
        if (newValue == Priority.defaultPriority) {
            //action here.
        } else if (newValue == Priority.lowPriority) {
            //action here.
        } else if (newValue == Priority.mediumPriority) {
            //action here.
        } else if (newValue == Priority.highPriority) {
            //action here.
        }
    }
}

That being said, I'm not sure why you've got that if / else-if in your getter; simply returning _priority should do exactly the same thing:

get {
    return _priority
}

You can actually simplify things even further by using property observers on a standard (ie non-computed) property:

var priority : Priority {
    didSet {
        if (self.priority == Priority.defaultPriority) {
            //action here.
        } else if (self.priority == Priority.lowPriority) {
            //action here.
        } else if (self.priority == Priority.mediumPriority) {
            //action here.
        } else if (self.priority == Priority.highPriority) {
            //action here.
        }
    }
}

Note: Doing it that way, you don't need the _priority property anymore since you're not implementing a customer getter and setter.

And, just for completeness, I'd probably use a switch statement instead of an if / else-if :

var priority: Priority {
    didSet {
        switch self.priority {
        case .lowPriority:
            // action here
        case .mediumPriority:
            // action here
        case .highPriority:
            // action here
        case .defaultPriority:
            // action here
        }
    }
}