Swift检查类是否符合协议始终为true

Question

protocol Device {
}
protocol ActiveDevice: Device {
}
protocol NoActive: Device {
}

ViewController:

class ViewController : UIViewController {
  let device: Device
}

Setting device for ViewController. currentDevice is an object which conforms to protocol Device

vc.device = currentDevice as! ActiveDevice

Checking if it conforms to the protocol:

    if let currentDevice = device as? NoActive  {
        print("Its not active device")
    }else if let currentDevice = device as? ActiveDevice {
        print("Its active device")
    }else {
        print("Its just a device")
    }

It always prints Its not active device what I would expect in this case that it would print Its active device

Answer 1

Please check the following code and let me know if this helps.

protocol Device {
}
protocol ActiveDevice: Device {
}
protocol NoActive: Device {
}

// class TestDevice: Device {
// class TestDevice: ActiveDevice {
class TestDevice: NoActive {

}

let currentDevice = TestDevice()

// let device: Device = currentDevice as! ActiveDevice
(It threw error as "Could not cast value of type '__lldb_expr_9.TestDevice' (0x11a2f9090) to '__lldb_expr_9.ActiveDevice' (0x11a6d0628)."). We cannot do this.

let device: Device = currentDevice


if device is NoActive  {
    print("Its not active device")
}else if device is ActiveDevice {
    print("Its active device")
}else {
    print("Its just a device")
}

Now, the output is "Its not active device". And after changing the TestDevice to "ActiveDevice", it printed "Its active device" and so on.