在数组Swift iOS中覆盖旧对象

Question

I have an array of custom objects. For simplicity, lets say each object has 3 properties : id , timestamp and text . I am now obtaining a JSON response from my server which contains updated text for my objects in the array. I need to do the following :

1. Obtain the object with the given id from my array.
2. Set the text of the object to the updated text WITHOUT changing any of its other properties.
3. Override the old object with the new and updated one.

I have found the following extension which allows me to find the object in my array.

 extension CollectionType {
func find(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element? {
    return try indexOf(predicate).map({self[$0]})
}
}

I am then using the following logic to obtain the item from the array.

let my_object =  questionImageObjects.find({$0.id== myId})

Now I set the text using my_object.text = currText .

The last step is to override the old object in the array with the updated one. This is where I am stuck.

Answer 1

The extension find will return a copy of the original struct. Whatever you do to it, the original won't be affected. You can modify it through the index:

struct DataModel: CustomStringConvertible {
    var id: Int
    var timestamp: NSDate
    var text: String

    init(id: Int, timestamp: NSDate, text: String) {
        self.id = id
        self.timestamp = timestamp
        self.text = text
    }

    // For debug purposes
    var description: String {
        get { return "( id = \(id), timestamp = \(timestamp), text = \(text) )" }
    }
}

// Initial data
var arr = [
    DataModel(id: 1, timestamp: NSDate(), text: "Anakin Skywalker"),
    DataModel(id: 2, timestamp: NSDate(), text: "Luke Skywalker")
]

// Now the server returns a JSON that says Anakin has turned to the Dark Side
let jsonString = "{ \"id\": 1, \"text\": \"Darth Vader\" }"
let jsonData = jsonString.dataUsingEncoding(NSUTF8StringEncoding)!
let json = try! NSJSONSerialization.JSONObjectWithData(jsonData, options: [])

// Update the text
if let dict = json as? [String: AnyObject],
    let id = dict["id"] as? Int,
    let newText = dict["text"] as? String,
    let index = (arr.indexOf { $0.id == id }) {

    arr[index].text = newText
}

print(arr)

If those if let s confuse you, here's a step-by-step guide:

• if let dict checks that the JSON can be converted into a Dictionary
• let id checks that it has an id key of type Int
• let newText checks that it has a text key of type String
• let index checks that the array contains an element with that id