Swift - 从类中附加数组时遇到问题

Question

我无法理解为什么当我尝试追加以下代码时，它会用最新信息替换我的所有数组元素。

我有以下课程：

class usersAvailable {
    var username = String()
    var userAvatar = UIImage()
}

我定义了以下变量以使用该类：

//the array which will hold users available to follow
    var usersAvailableArray = [usersAvailable]()
    var aUser = usersAvailable()

为了检查我的理智，我还声明了一个“常规”数组，看看我是否得到了正确的值：

var usersArray:[[String]] = [["",""]]

当我执行以下代码时：

func getAllUsers() {

        usersAvailableArray.removeAll(keepCapacity: true)
        usersArray.removeAll(keepCapacity: true)
        var query = PFQuery(className: "_User")
        query.findObjectsInBackgroundWithBlock {
            (objects: [AnyObject]?, error: NSError?) -> Void in
            if error == nil {
                for object in objects! {
                  self.aUser.username = object["username"] as! String
                    println("aUser.username before append: \(self.aUser.username)")
                    println(self.aUser)
                    self.usersAvailableArray.append(self.aUser)
                    self.usersArray.append([self.aUser.username])
                    println("first element of usersAvailableArray: \(self.usersAvailableArray.first?.username)")
                    println("last element of usersAvailableArray: \(self.usersAvailableArray.last?.username)")
                    println("number of elements currently in usersAvailableArray: \(self.usersAvailableArray.count)")
                    println("first element of usersArray: \(self.usersArray.first)")
                    println("last element of usersArray: \(self.usersArray.last)")
                    println("number of elements currently in usersArray: \(self.usersArray.count)")
 }

这是我得到的控制台输出：

aUser.username before append: joeBob
ParseStarterProject.usersAvailable
first element of usersAvailableArray: Optional("joeBob")
last element of usersAvailableArray: Optional("joeBob")
number of elements currently in usersAvailableArray: 1
first element of usersArray: Optional(["joeBob"])
last element of usersArray: Optional(["joeBob"])
number of elements currently in usersArray: 1
aUser.username before append: monkey
ParseStarterProject.usersAvailable
first element of usersAvailableArray: Optional("monkey")
last element of usersAvailableArray: Optional("monkey")
number of elements currently in usersAvailableArray: 2
first element of usersArray: Optional(["joeBob"])
last element of usersArray: Optional(["monkey"])
number of elements currently in usersArray: 2
aUser.username before append: support
ParseStarterProject.usersAvailable
first element of usersAvailableArray: Optional("support")
last element of usersAvailableArray: Optional("support")
number of elements currently in usersAvailableArray: 3
first element of usersArray: Optional(["joeBob"])
last element of usersArray: Optional(["support"])
number of elements currently in usersArray: 3

为什么我追加的 usersAvailableArray 会替换数组 UsersAvailableArray 中的每个元素？

Answer 1

您通过引用将数据传递给数组，并且在每个循环中您都会更改引用的值：

self.aUser.username = object["username"] as! String
self.usersAvailableArray.append(self.aUser)

尝试每次创建一个新用户：

var newUser = usersAvailable()
newUser.username = object["username"] as! String
self.usersAvailableArray.append(newUser)

发生这种情况是因为您附加的对象来自一个类，来自appe documentation：

类是引用类型

与值类型不同，引用类型在被复制时不会被复制 分配给变量或常量，或者当它们被传递给 功能。而不是副本，而是对相同现有的引用 而是使用实例。您可以查看有关值和参考的更多信息 在斯威夫特

另一种解决方案是将您的类更改为结构，如下所示，如果类在传递值时复制值而不是传递引用，则结构不同。

struct usersAvailable {
    var username = String()
    var userAvatar = UIImage()
}