Swift 中一个数组中的不同结构

Question

I have a struct called trip .

struct trip {
    var name: String
    var description: String
    var elements: [Any] = []

    mutating func addItemToElements(newValue: Any) {
       elements.append(newValue)
    }
}

As you can see, there is an array inside. I'm adding some other structs like element_flight into this array by function addItemtoElements .

struct element_flight {
    var origin: String
    var destination: String
    var flightno: String
    var departure: NSDate
    var arrival: NSDate
    var seat: String
}

Then I'm trying to create a list using table view:

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "elementTrip", for: indexPath) as! CellInElementsOfTripsTableViewCell
    let elem = trips[0].elements[indexPath.row]
    cell.mainTextLabel.text = elem.origin //it doesn't work

    return cell
}

I can't get any of parts of struct (like origin in code). What am I doing wrong?

I'm creating similar structs to element_flight and it could be the best way to put it in one array and then show in table view.

Answer 1

A simple, naive solution would be to cast elem to the correct type:

cell.mainTextLabel.text = (elem as! element_flight).origin

However, since the elements array can store Any , what if elem is some other type? Obviously, it will crash!

I don't understand why you want to store a bunch of Any in elements . This is a sign or bad code. Any is seldom used in Swift.

If you're just going to store some types, but not Any types, in elements , create a protocol and make all the types that you want to store conform to it. At least you get a little bit of type safety.

Let's say your array will only contain two structs: element_flight and SomeOtherStruct . You should do something like this:

protocol SomeProtocol { // please give this a proper name yourself
    // properties/methods that are common among element_flight and SomOtherStruct
}

struct element_flight: SomeProtocol {
    // ...
}

struct SomeOtherStruct: SomeProtocol {
    // ...
}

And change the array to be of type [SomeProtocol] .

Now in the cellForRowAtIndexPath method, you need to test whether elem is element_flight or SomeOtherStruct :

if let flight = elem as? element_flight {
    cell.mainTextLabel.text = flight.origin
} else if let someOtherStuff = elem as? SomeOtherStruct {
    // do some other stuff
} else {
    // something's wrong if this is executed, maybe call fatalError
}

Answer 2

You should cast them to FlightInfo (use this name instead of element_flight - type name in Swift should be written in CamelCase).

override func tableView(_ tableView: UITableView, 
           cellForRowAt indexPath: IndexPath) -> UITableViewCell {
  let cell = tableView.dequeueReusableCell(withIdentifier: "elementTrip", 
                     for: indexPath) as! CellInElementsOfTripsTableViewCell

  if let flightInfo = trips[0].elements[indexPath.row] as? FlightInfo {
    cell.mainTextLabel.text = flightInfo.origin //it doesn't work
  }

  return cell
}

Answer 3

另一种方法是将不同的结构存储在Any数组中，并在将其复制到变量之前使用is变量来测试类型。