如何向下浇铸UIViewController Swift

Question

base ViewController

import UIKit

class SubViewPost: UIViewController {

    @IBOutlet weak var content: UILabel!

    @IBOutlet weak var recommendCount: UILabel!
    @IBOutlet weak var recommendButton: UIButton!

    var postInfo:PostInfo!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

child ViewController

import UIKit

class SubViewOne: SubViewPost {

    @IBAction func likeWorry(_ sender: Any) {
        Option.recommend(postInfo: postInfo, mRecommendCount: recommendCount, mRecommendButton: recommendButton)

    }



}

and another child viewController

import UIKit

class SubViewTwo: SubViewPost {

    override func viewDidLoad() {
        recommendCount.alpha=0
        recommendButton.alpha=0
    }


}

i want add subviewOne or SubViewTwo

My ParentView

var subViewPost:SubViewPost

 if postType == 1{
 subViewPost = storyboard?.instantiateViewController(withIdentifier: "SubViewPost") as! SubViewOne
 }else{
subViewPost = storyboard?.instantiateViewController(withIdentifier: "SubViewPost") as! SubViewTwo
 }

 containerView.addSubview(subViewPost.view)

raise error

Could not cast value of type 
'MyApp.SubViewPost' (0x101151728) to 'MyApp.SubViewOne' (0x10114d9d0).

2018-07-10 14:40:56.007436+0900 MyApp[7207:209932] 
Could not cast value of type 'MyApp.SubViewPost' (0x101151728) to 'MyApp.SubViewOne' (0x10114d9d0).

how to chagne view controller by According to postType

SubView One have Recommned

but SubView Two haven't Recommend

SubView 1,2 have same UI

Answer 1

The error message is clear. When you say

storyboard?.instantiateViewController(withIdentifier: "SubViewPost")

what you get from the storyboard is a view controller whose class is SubViewPost. You cannot wave a magic casting wand and claim that it is a SubViewOne instead; it isn't.

If you wanted this view controller to be a SubViewOne, then you should have declared it as a SubViewOne in the storyboard in the Identity inspector.

---

I think I see what you are trying to do, and why you are confused about why you can't do it this way.

What's in the storyboard is an instance , not a class. Yes, it is an instance of some class, but it is an instance of that class. So when you design the interface in the storyboard, you are designing the interface associated with that one instance of that one class.

If your goal is to have a single interface associated with multiple classes , the interface must be generated in code or loaded from a View .xib file — not designed in a storyboard.

---

However, you would be better off not trying to use subclassing in this situation in the first place. What I do in a similar situation is give my view controller an enum property that says which "kind" of view controller it is, and obey accordingly in code. That a way, a single class serves multiple purposes.

Answer 2

The UViewController class for your scene "SubViewPost" in your storyboard is set to SubViewPost and that is what instantiateViewController will be returning. You cannot downcast an instance of SubViewPost to SubViewOne or SubViewTwo .

You could define two identical scenes in your storyboard, each with the appropriate view controller class, but that would require a lot of duplication.

Since the only difference is the visibility of the recommendButton and recommendCount elements, why not just handle that via a property:

var subViewPost = storyboard?.instantiateViewController(withIdentifier: "SubViewPost") as! SubViewPost

subViewPost.recommendVisible = (postType == 1)

SubViewPost.swift

var recommendVisible = true 

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    recommendCount.isHidden = !recommendVisible
    recommendButton.isHidden = !recommendVisible
}