Delegate 在 Swift 程序中为零

Question

I'm practising how to communicate between two view controllers using protocol and delegate (in the xCode background even when I'm using protocol in my project I get the same problem, Delegate is nil), but the problem after setting everything it shows me that my delegate is nil and the sender VC does not send any data since the delegate is nil.

I have confirmed to the protocol and I have set the receiver VC as the delegate, but still can not see where the problem is.

The Protocol

protocol theCommunicationsStructionProtocol{

func dataToTransmit(Data: String)

}

The Sender VC

class TheSenderVC{

var delegate: theCommunicationsStructionProtocol?

func lookingForDelegate(){


self.delegate?.dataToTransmit(Data: "Data has been sent")

 }
}

The Receiver VC

class TheReceiverVc1: theCommunicationsStructionProtocol{
var TheSenderVCObj = TheSenderVC()

func delegateLuncher(){

TheSenderVCObj.delegate = self
}

func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
 }

}

calling delegateLuncher() to set the delegate in the receiver VC

TheSenderVC().lookingForDelegate()

calling lookingForDelegate() from the sender VC to look for the delegate and send it the data

TheReceiverVc1().delegateLuncher()

Note: I have tried accessing the delegate from the receiver VC using this way:

class TheReceiverVc1: theCommunicationsStructionProtocol{
 var TheSenderVCObj: TheSenderVC?

func delegateLuncher(){

self.TheSenderVCObj?.delegate = self
}

func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
 }

}  

but I still getting the same problem:

delegate is nil

Answer 1

Finally, I found the solution! the problem is I was making instances of the TheSenderVC, instead of takling to the original TheSenderVC. when I was making an object (an instance) of TheSenderVC the problem occurred! instead I have to access the original TheSenderVC, which means I have to use static :)

here is the old delegate set up

var delegate: theCommunicationsStructionProtocol?

from TheSenderVC

here is the new delegate set up

static var delegate: theCommunicationsStructionProtocol?

therefore the

func lookingForDelegate(){


self.delegate?.dataToTransmit(Data: "Data has been sent")

}

will be changed to

static func lookingForDelegate(){


self.delegate?.dataToTransmit(Data: "Data has been sent")

}

since now it includes a static property (delegate)

on the other hand, the The ReceiverVC1 should be changed from:

class TheReceiverVc1: theCommunicationsStructionProtocol{
var TheSenderVCObj = TheSenderVC()

func delegateLuncher(){

TheSenderVCObj.delegate = self
}

func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
   }

  }

to:

class TheReceiverVc1: theCommunicationsStructionProtocol{


func delegateLuncher(){

TheSenderVC.delegate = self
}

func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
}

}

accessing the delegate from the original TheSenderVC()

Answer 2

Where are you create the reference of TheSenderVCObj

replace var TheSenderVCObj: TheSenderVC? to var TheSenderVCObj = TheSenderVC()

let try below code:

class TheReceiverVc1: theCommunicationsStructionProtocol{
 var TheSenderVCObj = TheSenderVC()

func delegateLuncher(){

self.TheSenderVCObj?.delegate = self
}

func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
 }

}  

your TheSenderVCObj also nil according to your code.

NOTE: use proper naming conventions.

Answer 3

Because the TheReceiverVc1 was automatic deinit by ARC . You need to save reference of the instance like that's:

class ViewController: UIViewController {
    let theReceiverVc1: TheReceiverVc1 = TheReceiverVc1()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        theReceiverVc1.delegateLuncher()
    }
}

Also make sure when you using delegate set it as weak var:

weak var delegate: theCommunicationsStructionProtocol?