在Swift中为特定方法调用实现闭包

Question

I came across the following UITableViewController code and wanted to implement the associated classes and functions that go with them in order for me to learn a little bit more about Swift.

I'm not sure what the implementation of api.getRooms() looks like. I think it may be a closure, but I'm not entirely sure?

My question is what would api.getRooms() be returning considering there's {} usage? If anyone could explain to me what's going on that would be greatly appreciated.

api.getRooms(User.currentUser()!) { (roomsObj, error) in
    if let rooms = roomsObj as? Array<Room> {
        self.rooms = rooms
        self.tableView.reloadData()
        if (viaPullToRefresh) {
            self.refreshControl.endRefreshing()
        }
    }
}

PullViewController.swift

class PullViewController: UITableViewController {
    var rooms = Array<Room>()

    init(coder aDecoder: NSCoder!) {
        super.init(coder: aDecoder)

        // Custom initialization
        assert(User.currentUser())
    }

    override func viewDidLoad() {
        self.refreshControl = UIRefreshControl()
        self.refreshControl.addTarget(self, action: Selector("refreshInvoked"), forControlEvents: UIControlEvents.ValueChanged)
        refresh()
    }

    override func tableView(tableView: UITableView!, numberOfRowsInSection section: Int) -> Int {
        return rooms.count
    }

    override func tableView(tableView: UITableView!, cellForRowAtIndexPath indexPath:NSIndexPath!) -> UITableViewCell! {
        var cell: UITableViewCell? = tableView.dequeueReusableCellWithIdentifier("Cell") as? UITableViewCell
        if !cell {
            cell = UITableViewCell(style: UITableViewCellStyle.Default, reuseIdentifier:"Cell")
        }

        let room = rooms[indexPath.row]
        cell!.textLabel.textColor = UIColor.blackColor()
        cell!.textLabel.text = "\(room.name)(\(room.messageCount))"
        return cell
    }

    func refreshInvoked() {
        refresh(viaPullToRefresh: true)
    }

    func refresh(viaPullToRefresh: Bool = false) {
        let api = API()
        api.getRooms(User.currentUser()!) { (roomsObj, error) in
            if let rooms = roomsObj as? Array<Room> {
                self.rooms = rooms
                self.tableView.reloadData()
                if (viaPullToRefresh) {
                    self.refreshControl.endRefreshing()
                }
            }
        }
    }
}

User.swift

class User {

    init() {
    }

    class func currentUser() -> Bool {
        return true
    }
}

Room.swift

class Room {

    var name: String
    var messageCount: Int

    init() {
    }
}

API.swift (not sure whether this is implemented correctly).

class API {

    init() {
    }

    func getRooms(user: User) -> (Array<Room>, String) { // ??
        // ??
    }
}

Answer 1

1) You are sending assert a void since your currentUser method doesn't return anything, so assert wouldn't know if this is good or bad. Therefore you need to make currentUser return a BOOL or something else if you want to use it like this, but it needs some sort of BOOL result to tell if it is asserting correctly or not. Hopefully that makes sense.

2)You are trying to feed your getRooms function a lambda function instead of running a function after the results.

--Update-- If you are wanting a completion lambda then you'll want to write getRooms like this:

func getRooms(user: User, completion: ((Array<Room>,String?) -> Void)?) -> Array<Room> {//String because I have no idea what type they want for errors
    var room = Room()

    room.messageCount = 0
    room.name = "Room1"

    var rooms = Array<Room>()
    rooms.append(room)

    completion?(rooms,nil)

    return rooms
}

or something along those lines

Answer 2

In you room class, you did not initialize the name and message count variable, in swift only optional variable can be nil

class Room {

    var name: String
    var messageCount: Int

    init(name:String, messageCount:Int) {
        self.name = name
        self.messageCount = messageCount
    }
}

also assert need to evaluate to bool so

assert(User.currentUser() != nil)

Answer 3

This is how I implemented the api.getRooms() function:

API.swift

class API {

    func getRooms(user: User, completion: (Array<Room>, String) -> ()) {
        var room = Room(name: "Room1", messageCount: 0)

        var rooms = Array<Room>()
        rooms.append(room)

        completion(rooms, "error")
    }

}

PullViewController.swift

func refresh(viaPullToRefresh: Bool = false) {

    let api = API()

    if let user = User.currentUser() {
        api.getRooms(user) { (roomsObj, error) in
            self.rooms = roomsObj
            self.tableView.reloadData()
            if (viaPullToRefresh) {
                self.refreshControl.endRefreshing()
            }
        }
    }

}