ios - 在 Swift iOS 中为协议(protocol)分配委托(delegate)时出现编译器错误

Question

我在为对象分配委托(delegate)时遇到问题，该对象是在 Swift 中定义协议(protocol)的类的实例，如下所示:

我将代码简化为最基本的部分以举例说明问题:这是带有协议(protocol)的类

protocol TheProtocol {
    func notifyDelegate()
}
class ClassWithProtocol: NSObject {   
    var delegate: TheProtocol?
    fire() {
        delegate?.notifyDelegate()
    }
}

这是符合协议(protocol)的类

    class ClassConformingToProtocol: NSObject, TheProtocol {
        var object: ClassWithProtocol?
        func notifyDelegate() {
            println("OK")
        }
        init() {
            object = ClassWithProtocol()
            object?.delegate = self  // Compiler error - Cannot assign to the result of this expression 
            object?.fire()
        }
    }

我尝试了各种替代方法来分配委托(delegate)，但都没有成功。知道我错过了什么吗？

Answer 1

发行说明的已知问题部分说:

You cannot conditionally assign to a property of an optional object. (16922562)

For example, this is not supported:

let window: NSWindow? = NSApplication.sharedApplication.mainWindow
window?.title = "Currently experiencing problems"

所以你应该做类似if let realObject = object { ... }