如何从变量访问属性或方法？

Question

是否可以在 Swift 中使用变量作为方法或属性的名称来访问方法或属性？

在 PHP 中，您可以使用 $object->{$variable}。例如

class Object {
  public $first_name;
}

$object = new Object();
$object->first_name = 'John Doe';

$variable = 'first_name';
$first_name = $object->{$variable}; // Here we can encapsulate the variable in {} to get the value first_name
print($first_name);
// Outputs "John Doe"

编辑：

这是我正在使用的实际代码：

class Punchlist {
    var nid: String?
    var title: String?

    init(nid: String) {

        let (result, err) = SD.executeQuery("SELECT * FROM punchlists WHERE nid = \(nid)")
        if err != nil {
            println("Error")
        }
        else {
            let keys = self.getKeys()  // Get a list of all the class properties (in this case only returns array containing "nid" and "title")
            for row in result {  // Loop through each row of the query
                for field in keys {  // Loop through each property ("nid" and "title")
                    // field = "nid" or "title"
                    if let value: String = row[field]?.asString() {
                        // value = value pulled from column "nid" or "title" for this row
                        self.field = value  //<---!! Error: 'Punchlist' does not have a member named 'field'
                    }
                }
            }
        }
    }

    //  Returns array of all class properties
    func getKeys() -> Array<String> {
        let mirror = reflect(self)
        var keys = [String]()
        for i in 0..<mirror.count {
            let (name,_) = mirror[i]
            keys.append(name)
        }

        return keys
    }
}

Answer 1

下标可能会对您有所帮助。

let punch = Punchlist()
punch["nid"] = "123"
println(punch["nid"])

class Punchlist {
    var nid: String?
    var title: String?

    subscript(key: String) -> String? {
        get {
            if key == "nid" {
                return nid
            } else if key == "title" {
                return title
            }
            return nil
        }
        set {
            if key == "nid" {
                nid = newValue
            } else if key == "title" {
                title = newValue        
            }
        }
    }
}

Answer 2

你可以做到，但不能使用“纯”Swift。 Swift（作为一种语言）的全部意义在于防止那种危险的动态属性访问。您必须使用 Cocoa 的 Key-Value Coding 功能：

self.setValue(value, forKey:field)

非常方便，它恰好穿过了您想要穿过的字符串到属性名称的桥梁，但要注意：这里是龙。

（但如果可能，最好将架构重新实现为字典。字典具有任意字符串键和对应值，因此没有可跨越的桥梁。）