There's a NavigationController which has a ViewController as a rootViewController
In this ViewController I declare a panGestureRecogniser like this:
guard let thisNavigationController = navigationController as? ProfileNavigationController else { return }
let panDown = UIPanGestureRecognizer(target: thisNavigationController, action: #selector(handleGesture))
panDown!.delegate = self
collectionView.addGestureRecognizer(panDown!)
As you can see I set the target of this gesture to be the navigationController of the viewController that I have previously carefully downcasted to its type.
The method handleGesture has been correctly declared and set to public in its own NavigationController class, in fact in ProfileNavigationController class I have set and declared public:
#objc public func handleGesture(_ gesture: UIPanGestureRecognizer){
However I have this error Cannot find 'handleGesture' in scope in ViewController as if I should declare this method in viewController too even if the target is set to the navigationController.
If I don't set the method also in the ViewController (even if it's empty) the code won't run and I don't know why is that.
If I set it empty in the viewController everything works fine. How can I solve this?
You should use selector of ProfileNavigationController like:
let panDown = UIPanGestureRecognizer(target: thisNavigationController, action: #selector(ProfileNavigationController.handleGesture))
Related
I am new to Swift and Xcode. I am building an Financial Expense ios app.
In my first view controller, I created a referencing outlet for a label called expenseNum.
In my second view controller, I have a function for a button called Add Expense. When it is clicked, I need it to update the expenseNum variable with the amount of the expense.
What is the best way to go about this? I had created an object of the first view controller class and accessed it like "firstviewcontroller.expenseNum" but this will create a new instance of the class and I need it to be all the same instance so it can continuously add to the same variable. Thanks for the help!
You need a delegate
protocol SendManager {
func send(str:String)
}
In first
class FirstVc:UIViewcontroller , SendManager {
func send(str:string) {
self.expenseNum.text = str
}
}
when you present SecondVc
let sec = SecondVc()
sec.delegate = self
// present
In second
class SecondVc:UIViewcontroller {
var delegate:SendManager?
#IBAction func btnClicked(_ sender:UIButton) {
delegate?.send(str:"value")
}
}
// setting delegate
in viewDidLoad of SecondVc
if let first = self.tabBarController.viewControllers[0] as? FirstVc {
self.delegate = first
}
There are several ways you can pass data from ViewController2 to another ViewController1
The best way here is Protocol Delegates
Please follow below steps to pass data
In Your SecondViewController from where you want to send data back declare a protocol at the top of class declaration
protocol SendDataBack: class {
func sendDataFromSecondVCtoFirstVC(myValue: String)
}
Now in the class , declare a object of your protocol in same ViewController
weak var myDelegateObj: SendDataBack?
And now in your Add Expense button action just call the delegate method
myDelegateObj?.sendDataFromSecondVCtoFirstVC(myValue: yourValue)
Now go to your first ViewController
the place from where you have pushed/present to SecondViewController you must have taken the object of SecondVC to push to push from first
if let secondVC = (UIStoryboard.init(name: "Main", bundle: nil)).instantiateViewController(withIdentifier: "secondVCID") as? SecondViewController {
vc?.myDelegateObj = self
self.navigationController?.pushViewController(secondVC, animated: true)
**OR**
self.present(secondVC, animated: true, completion: nil)
}
now in your FirstViewController make an extension of FirstViewVC
extension FirstViewController: SendDataBack {
func sendDataFromSecondVCtoFirstVC(myValue: String) {
}
}
I think you can make a variable in your properties in second ViewController (before viewDidLoad method)
var delegate: FirstViewController? = nil
and use from the properties of the first view controller anywhere of the second view controller.
delegate!.mainTableView.alpha=1.0
//for example access to a tableView in first view controller
The simplest way to achieve this is to use a public var. Add a new Swift file to your project, call it Globals. Declare the public variable in Globals.swift like so:
public var theValue: Int = 0
Set its required value in the first ViewController, and you'll find you can read it in the second with ease.
Im new to swift and iOS development.I have a doubt regarding protocol and delegate methods.
I have a 4 vc's say vc1,vc2,vc3,vc4.And i'm navigating from vc1->vc2->vc3-vc4->vc1. That is from vc4, im poping using navigation controller back to vc1.
i have a protocol and methods in it like
protocol myProtocol{
func myFunc()
}
In vc4, im making a delegate as,
var delegate:myProtocol?
and im using it in a button action as
if let delegate = self.delegate{
delegate.myFunc()
}
and also pop vc4 back to vc1.
Now in VC1,im extending myProtocol as
class vc1:myProtocol{
override func viewDidLoad()
{
let vcProtocol = vc4()
vc4.delegate = self
}
func myFunc()
{
print("executing this")
}
}
But its not working. Can i do like this?
How can i connect these to classes with delegate and protocol.Please help me
viewDidLoad is only executed once if the controller is not destroyed.
Try calling in viewWillAppear for example.
Also, you do not need to change the delegate of vc4, just set the delegate to vc1 again (in viewWillAppear).
Have you tried Notification?
In your VC1 ViewController ViewDidLoad method:
NotificationCenter.default.addObserver(self, selector: #selector(myFunc, name: NSNotification.Name(rawValue: "aNotificationName"), object: nil)
In your VC4 when the myFunc is needed:
NotificationCenter.default.post(name: Notification.Name("aNotificationName"), object: nil)
You can get the viewController from the navigation stack which has the same type as your first viewController and then assign it as the delegate object in your vc4.
For instance:
In vc4's viewDidLoad, you may do this
for viewController in self.navigationController?.viewControllers{
if viewController.isKindOfClass(YourVC1ControllerType){
self.delegate = viewController
}
}
I assume that your vc1,vc2,vc3, etc have their own ViewController custom classes.
Another way of implementing this would be to get the first controller from the self.navigationController?.viewControllers array and setting it as the delegate object in vc4.
//In viewDidLoad of vc4
delegate = self.navigationController?.viewControllers.first as! HomeController
or,
//In viewDidLoad of vc4
delegate = self.navigationController?.viewControllers.[indexOfTheController] as! HomeController
I have just started translating my app to Swift, I want the CBCentralManager.delegate to be set to another view controller(One that navigation controller pushes onto).
I am trying to do the same with following code:
let viewCont = self.storyboard!.instantiateViewControllerWithIdentifier("mainView")
self.navigationController?.pushViewController(viewCont, animated: true)
manager.delegate = viewCont
The variable manager is an instance of CBCentralManager and setting delegate to viewCont raises following error:
"Cannot assign value of type 'UIViewController' to type 'CBCentralManagerDelegate?'"
The declaration for the view Controller:
class MainViewController: UIViewController, CBCentralManagerDelegate
How can I solve the same?
You need to downcast the view controller you receive from instantiateViewControllerWithIdentifier. Without the downcast, all the compiler knows is that you have a UIViewController
let viewCont = self.storyboard!.instantiateViewControllerWithIdentifier("mainView") as! MainViewController
self.navigationController?.pushViewController(viewCont, animated: true)
manager.delegate = viewCont
Once you have the downcast using as! then the compiler knows that it has a MainViewController and since this class is also a CBCentralManagerDelegate it is happy.
I have an optional bool variable called showSettings on my first view controller which is called ViewController, and I'm popping from SecondViewController back to ViewController.
Before I pop, I want to set the bool to true. Seems wrong to instantiate another view controller since ViewController is in memory.
What's the best way to do this? I'm not using storyboards, if that's important for your answer.
Thanks for your help
So I figured it out, based mostly from this post – http://makeapppie.com/2014/09/15/swift-swift-programmatic-navigation-view-controllers-in-swift/
In SecondViewController, above the class declaration, add this code:
protocol SecondVCDelegate {
func didFinishSecondVC(controller: SecondViewController)
}
Then inside of SecondViewContoller add a class variable:
var delegate: MeditationVCDelegate! = nil
Then inside of your function that your button targets, add this:
self.navigationController?.popViewControllerAnimated(true)
delegate.didFinishSecondVC(self)
What we're doing here is doing the pop in SecondViewController, and not passing any data, but since we've defined a protocol, we're going to use that in ViewController to handle the data.
So next, in ViewController, add the protocol you defined in SecondViewController to the list of classes ViewController inherits from:
class ViewController: UIViewController, SecondVCDelegate { ... your code... }
You'll need to add the function we defined in the new protocol in order to make the compiler happy. Inside of ViewController's class, add this:
func didFinishSecondVC(controller: SecondViewController) {
self.myBoolVar = true
controller.navigationController?.popViewControllerAnimated(true)
}
In SecondViewController where we're calling didFinishSecondVC, we're calling this method inside of the ViewController class, the controller we're popping to. It's similar to if we wrote this code inside of SecondViewController but we've written it inside of ViewController and we're using a delegate to manage the messaging between the two.
Finally, in ViewController, in the function we're targeting to push to SecondViewController, add this code:
let secondVC = secondViewController()
secondVC.delegate = self
self.navigationController?.pushViewController(secondVC, animated: true)
That's it! You should be all set to pass code between two view controllers without using storyboards!
_ = self.navigationController?.popViewController(animated: true)
let previousViewController = self.navigationController?.viewControllers.last as! PreviousViewController
previousViewController.PropertyOrMethod
I came across this while looking for a way to do it. Since I use Storyboards more often, I found that I can get the array of controllers in the navigation stack, get the one just before the current one that's on top, check to see if it's my delegate, and if so, cast it as the delegate, set my methods, then pop myself from the stack. Although the code is in ObjC, it should be easily translatable to swift:
// we need to get the previous view controller
NSArray *array = self.navigationController.viewControllers;
if ( array.count > 1) {
UIViewController *controller = [array objectAtIndex:(array.count - 2)];
if ( [controller conformsToProtocol:#protocol(GenreSelectionDelegate)]) {
id<GenreSelectionDelegate> genreDelegate = (id<GenreSelectionDelegate>)controller;
[genreDelegate setGenre:_selectedGenre];
}
[self.navigationController popViewControllerAnimated:YES];
}
Expanding upon the answer by Abdul Baseer Khan:
For cases where the current view controller may have been loaded by different types of previous view controller, we can use the safer as? call instead of as!, which will return nil if the controller is not what we were looking for:
let previousVC = self.navigationController?.viewControllers.last as? AnExampleController
previousVC?.doSomething()
Although, you would need to repeat that for each different view controller that could load the current view controller.
So, you may want to, instead, implement a protocol to be assigned to all the possible previous view controllers:
protocol PreviousController: UIViewController {
func doSomething()
}
class AnExampleController: UIViewController, PreviousController {
// ...
func doSomething() {}
}
class AnotherController: UIViewController, PreviousController {
// ...
func doSomething() {}
}
class CurrentController: UIViewController {
// ...
func goBack() {
let previousVC = self.navigationController?.viewControllers.last as? PreviousController
previousVC?.doSomething()
}
}
I have a main view controller that has been setup in Interface Builder to open a table view controller via popover segue connected to a button. I want to be able to dismiss the popover when an item inside of my popover table view is selected in didSelectRowAtIndexPath. In Objective-c I can just typecast the the segue in the prepareForSegue delegate to a UIStoryboardPopoverSegueand pass along its UIPopoverController to the table view controller. However, in Swift my downcast fails because it sees the segue as type UIStorybaordPopoverPresentationSegue (when stepping through with the debugger) which doesn't appear to be a public API.
Here's my code:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
if segue.identifier == "ShowCollectionsSegue" {
if let collController:CollectionsTableViewController! = segue.destinationViewController as? CollectionsTableViewController {
if let popoverSegue = segue as? UIStoryboardPopoverSegue { // <-- This fails
collController.popover = popoverSegue.popoverController
}
}
}
}
How do I coerce the segue to a UIStoryboardPopoverSegue in order to access its popoverController property?
I'm open to solving the problem of dismissing the popover in response to a table view cell tap a different way, but it seems that when using a segue from the storyboard, the only way to dismiss the popover is by holding onto a reference to the popover controller somehow and the only way to do that as far as I can tell is to cast the segue to a popover segue which Swift doesn't want to let me do. Any ideas?
A strange problem, indeed. I noticed in the documentation, that UIStoryboardPopoverSegue does not inherit from any class. That explains why the cast does not work - UIStoryboardSegue is not its superclass. So I just tried to create a new object - it looks weird but works:
let popoverSegue = UIStoryboardPopoverSegue(
identifier: segue.identifier,
source: self,
destination: segue.destinationViewController as UIViewController)
println("Is there a controller? \(popoverSegue.popoverController.description)")
// YES !!
EDIT
But this controller will not dismiss the popover :(
The fix is to specify the segue in Interface Builder as "Deprecated Segues : Popover". Then the code would be as expected
let popoverSegue = segue as UIStoryboardPopoverSegue
if let destination = segue.destinationViewController as? TableViewController {
destination.delegate = self
self.popoverController = popoverSegue.popoverController
}