问题
I have two views that I would like to pass data from one view to the next. The first view is where I have the data that I would like to pass to the next view lets call it SourceViewController. However SourceViewController is embedded in a NavigationViewController and the secondViewController lets call it DestinationViewController is the firstView in a TabViewController.
I have tried to use the answer from this question and it fails to go past navigation view it just skips the whole logic.
This is my code :
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if (segue.identifier == "loginSuccessSugue") {
if let tab = self.presentingViewController as? UITabBarController,
let nav = tab.viewControllers?[0] as? UINavigationController,
let destinationVC = nav.viewControllers.first as? HomeViewController {
destinationVC.currentBalance = serviceBalance
}
}
}
This is the HomeViewController:
class HomeViewController: UIViewController , UITableViewDelegate,UITableViewDataSource, UICircularProgressRingDelegate{
var currentBalance = 0.0
override func viewDidLoad() {
super.viewDidLoad()
circularBalance.maxValue = CGFloat(currentBalance)
print(currentBalance)
}
override func viewDidAppear(_ animated: Bool) {
print(currentBalance)
circularBalance.setProgress(value: CGFloat(currentBalance), animationDuration: 3)
}
}
This is how the storyboard looks like:
回答1:
This is my view controller where you can check that I am sending 5 to tabbar first viewcontroller:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
self.performSegue(withIdentifier: "segueIdentifier", sender: self)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let barViewControllers = segue.destination as! UITabBarController
let destinationNv = barViewControllers.viewControllers?[0] as! UINavigationController
let destinationViewController = destinationNv.viewControllers[0] as! FirstViewController
destinationViewController.currentBalance = 5
}
}
Now You can check my firstview controller where you can check that what value we are getting.
class FirstViewController: UIViewController {
var currentBalance = 0
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
print(currentBalance)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
Now, You can check my console and storyboard:
回答2:
From Apple's UIViewController docs:
var presentingViewController: UIViewController?
The view controller that presented this view controller.
Which would work great for you, ** IF ** you were trying to go back in your navigational hierarchy, as did the guy in the SO post you referenced.
You are trying cast the VC THAT PRESENTED SOURCEVIEWCONTROLLER of your SourceViewController as a UITabBarController, which fails miserably, and is why you never hit a breakpoint inside your nested if let's.
If we look the next variable down from this in the docs we can see something that will take us forward to the UIViewController we are presenting:
var presentedViewController: UIViewController?
The view controller that is presented by this view controller, or one of its ancestors in the view controller hierarchy.
So now to go over the code you need to solve your predicament. I'll give you the same code you posted, but fixing the tense of my verbs in the comments:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if (segue.identifier == "loginSuccessSugue") {
//ing -> ed
if let tab = self.presentingViewController as? UITabBarController,
let nav = tab.viewControllers?[0] as? UINavigationController,
let destinationVC = nav.viewControllers.first as? HomeViewController {
destinationVC.currentBalance = serviceBalance
}
}
Isn't it frustrating when the English language tricks you up more than swift?
EDIT:
Since you are passing the data in prepareForSegue: you will actually want to get the UITabBarController from segue.destination. And since the the UITabBarController's ViewControllers property will be nil or empty in prepare for segue. This is a bad approach for passing the data.
You may need to create custom subclass of UITabBarController, pass it the variable, and then pass that data to its viewControllers in viewDidLoad.
class MyTabBarController: UITabBarController {
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
var serviceBalance : Double?
override func viewDidLoad() {
super.viewDidLoad()
//Make sure vc is not null or empty before continuing.
guard let vcs = viewControllers, !vcs.isEmpty else {
return
}
if let navVC = vcs[0] as? UINavigationController, let destinationVC = navVC.viewControllers[0] as? UIViewController {
destinationVC.serviceBalance = destinationVC
}
}
}
Updated prepareForSegue:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let tabBarVC = segue.destination as? MyTabBarController {
tabBarVC.serviceBalance = serviceBalance
}
}
Don't forget to change the UITabBarController's class in the identity inspector of storyboard to MyTabBarController
回答3:
You need to change if() condition code.
Use below code will get your HomeViewController in destination of segue.
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if (segue.identifier == "loginSuccessSugue") {
if let destinationVC = segue.destination as? HomeViewController {
destinationVC.currentBalance = serviceBalance
}
}
}
As in segue.destination you will get your HomeViewController so no need to get it from Tab + Navigation stack.
Edit:
let destinationVC = segue.destination as? HomeViewController
Print(destinationVC)
Hope this solution will helps!
来源：https://stackoverflow.com/questions/49665361/passing-data-between-view-controllers-using-a-segue-from-a-view-embedded-in-a-na