For the following steps:
drag two view controllers using storyboard, add a button on the first VC
ctrl drag the button on the first VC to the second VC and choose present segue
embed first VC with navigation controller
My questions are:
What happens under the hood when program starts? In particular, how and where will be the first and second VC created?
If not same, what's the difference compared with code below?
let vc = storyboard.instantiateViewControllerWithIdentifier("someViewController") as! UIViewController
Swift code will be preferred but Objective-C is also fine. Thanks in advance.
What you are doing using:
let vc = storyboard.instantiateViewControllerWithIdentifier("someViewController") as! UIViewController
is that you are doing what the storyboard is supposed to do. You are forcefully preparing for the segue. When you simply connect the two views using the segue on the storyboard, you are telling the compiler that the connection exists. When you run the code the second viewcontroller is instantiated the instant you click on the button and performs a prepareForSegue.
All in all, its all about manually overriding the delegate methods that are called when the storyboard works.
Related
I am having a weird issue where my app crashes when I am trying to push a new view controller. I have set up a swipe gesture and want to segue to another view controller when a swipe is detected. When I run these 2 lines of code ...
let viewController:ViewController = ViewController()
self.navigationController?.pushViewController(viewController, animated: true)
The app crashes not specifically on either of those lines of code but rather in my ViewController class when in my viewDidLoad method I run this piece of code...
imageView.layer.masksToBounds = true
If I comment that out it crashes when I set the auto-correction type of my textField. What am I doing wrong?
First place I look when the view immediately crashes is in the Outlets for that ViewController in InterfaceBuilder. I look for anything that shows up with an exclamation mark. That usually means I renamed an outlet or broke a connection somehow. Delete anything broken by pressing the little x by the item that's messed up. I'll attach a photo so you can see.
It seems you're loading a ViewController that exists in storyboard with
let viewController:ViewController = ViewController()
which will result in nil outlets , so you have to use
let viewController = storyboard.instantiateViewController(withIdentifier: "VCID") as! ViewController
and give that vc a storyboard identifier like VCID
I think I have solved the issue but it has a weird side effect. Instead of using the line of code in #Sh_Khan's answer, I used ...
let viewController = nav?.storyboard!.instantiateViewController(withIdentifier: "mainVC") as! ViewController
The variable nav is equal to the navigation controller of the current view-controller. This seems to work without any hiccups but for some reason the back button does not disappear from the navigation controller after the segue is preformed. Does anybody know a solution to this, if so leave a comment and I will update my answer.
EDIT:
Another issue is that it wipes everything changed on that ViewController by the user clear. Is there another way to instantiate a ViewController without clearing it?
Follow what #Sh_Khan has said and in addition to that make sure that the view that you are making the push segue from is embedded in a Navigation controller.
i'm fairly new to swift, so please bear with me.
right now my problem can be broken down to this:
I have one Test View Controller that can display my 'Test' object by showing the description and the title. I also have an array of Test objects. In the top right hand corner, there is a 'skip this test' button, and if the user clicks on it, the viewcontroller will segue to itself, but change the Test object that is being displayed, e.g. its just basically looping through an array of Tests. I have changed the prepare for segue methods accordingly to push the data through the view controllers.
However, I want to be able to move to a completely different ViewController (lets just call it FinalViewController) if I have reached the last Test in my Test array.
Now this is the part that I can't fix.
I would like to create a segue directly from the 'skip test' button, only that it segues to a different view controller, depending on a certain condition. However, as i tried creating a segue in IB by right clicking on the Button and pulling it to the FinalViewController, it erased my previous segue I had for that button.
Does anybody know if there is a fix for this problem? thank you!!!!
However, as i tried creating a segue in IB by right clicking on the
Button and pulling it to the FinalViewController, it erased my
previous segue I had for that button
Actually, you don't want to do that, instead, you should drag from the controller itself, not from the button because if your segue has been created based on a button, tapping on it should always perform it and this is NOT what you want.
After creating a segue from the ViewController, you can -programmatically- call performSegue method and handle what data should be passed to the next viewController by implementing prepareForSegue method.
For more information, check my answer to know how to create multiple segues with identifiers and work with them.
EDIT:
If you want to push to the same current ViewController, performSegue method would not be the optimal solution. You should instead push/present to same ViewController it self:
class ViewController: UIViewController {
var myString: String?
override func viewDidLoad() {
super.viewDidLoad()
// here we go
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let sameViewController = storyboard.instantiateViewControllerWithIdentifier("ViewControllerStoryboardID") as! ViewController
sameViewController.myString = "the value of the new myString"
navigationController?.pushViewController(sameViewController, animated: true)
print(myString)
}
}
Probably, you don't want to implement it in viewDidLoad, it's just for demonstration purpose.
Make sure that the ViewController has a storyboard ID (in code snippet, I assume it is "ViewControllerStoryboardID"):
I have 4 ViewControllers in my storyboard. I want all of them to be able to access my "Settings" ViewController by performSegue.
Is it possible to have ONE segue to perform this, instead of ctrl + drag from each and every ViewController to my "Settings" ViewController?
No its not possible with a single segue. You need 4 different segues from 4 different ViewControllers. But you can do this programatically.
Make an extension for UIVIewController
extension UIViewController
{
func showSettingsScreen()
{
let storyBoard = UIStoryboard(name: "YourStoryBoardName", bundle:nil)
let settingsScreen = storyBoard.instantiateViewControllerWithIdentifier("YourSettingsViewControllerID")
self.navigationController?.pushViewController(settingsScreen, animated: true)
}
}
Now you can call showSettingsScreen() from any of your view controllers(Make sure this view controller has a navigation controller).
You cannot do that. A segue has only one source and one destination. You could programatically instantiate your Settings ViewController and display it either by using push or by using present. What you should think of though is why do you have to go to settings from so many places. It might be a sign of bad design and duplicate code. Usually applications have only one such button/action that can be accessed from multiple screens (by using some kind of container view implementation) or from only one screen.
I really dont think so there is a way to do so. U ought to connect ur SettingsViewController to all of your 4 View Controllers, add segue , and define a segue identifier which is used in
prepareForSegue:sender:
or
shouldPerformSegueWithIdentifier:sender:
methods. U can access segues through these identifiers. If u find "ctrl + drag from each and every ViewController to "Settings" ViewController " tasky you can opt for Navigation Controller as well. U just have to embed Navigation Controller in your storyboard and define Storyboard Id for every View Controller and you are done. Just use storyboard id of view controller to be instantiated and u good to go.
ViewController *vc = [self.storyboard instantiateViewControllerWithIdentifier:#"ViewController"];
[self.navigationController pushViewController:vc animated:YES];
Apart for assigning storyboard id you dont have to worry about storyboard ,No ctrl+drag thing.
I thought of one more elegant solution i.e. using Container View. You can take button to switch, SettingsViewController as common, in your Container View Controller while displaying every ViewController.
happy Coding..
There is one way to do this. Create a root view controller and matching view which contains a single embedded view. Add your segue to this root controller. Then in your app you switch in the other view controllers using standard child container techniques. This is pretty much the concept that UINavigationControllers use.
One advantage from this is that if you want to have common elements which are visible to all controllers then you can add them to your root controller.
But it all depends on what you are trying to achieve.
I'm trying to create a custom UIView that will, when tapped, segue to a new view controller. I'd like to do this programmatically rather than in Interface Builder. How do I get a reference to the destination view controller when I'm doing this? I assume I don't just create one and set it as the next view or something, so where does the reference come from? Since when it's done in the storyboard you simply choose where you want the segue to have as the destination, it's not an issue there, however programmatically I don't understand where that reference comes from.
I'm doing this in Swift as well. I don't think that really makes a big difference, but it might change something.
I tried using a UIView with a tapGestureRecognizer added, which then performed the segue when tapped, however I was getting an unrecognized selector error.
If you declared your UIViewController in storyboard you have to set its Storyboard Id, and then, instead of performing segue you can use something like this (didn't run it, but done exact the same thing in obj-c, so I think it will do well):
let storyboard : UIStoryboard = UIStoryboard(name: "myStoryboardName", bundle: nil);
let vc : MyUIViewController = storyboard.instantiateViewControllerWithIdentifier("myVCStoryboardID") as MyUIViewController;
self.presentViewController(vc, animated: true, completion: nil);
I have a tab bar controller and a few other viewcontrollers outside the tab bar controller. I have this viewcontroller called "X" which is a part of the tab bar controller. I have another viewcontroller called "Y" which is not a part of the tab bar controller. Now i want to initiate X when im inside Y upon tapping a button without actually presenting it. I want X to become active and fire its viewdidload so that i can access X whenever i chose to do so. Is this possible. Im sorry if im not clear in explaining my quiestion. let me know if you need any other additional information.
Old question at this point, but I was looking for an answer myself just yesterday and managed to get it figured out.
Instantiate the ViewController, then call loadViewIfNeeded().
Example:
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let exampleVC = storyboard.instantiateViewController(withIdentifier: "ExampleViewController") as! ExampleViewController
exampleVC.loadViewIfNeeded()
If you want, you can then check if the view is loaded with:
exampleVC.isViewLoaded
The ViewController is now all set up and ready for display when you decide to present it.
I want X to become active and fire its viewdidload so that i can access X whenever i chose to do so.
UIViewController uses lazy loading for the view property. You can just call:
[myViewController view];
This will trigger the loadView and/or viewDidLoad methods, if implemented.
However, you may wish to consider moving the relevant logic from viewDidLoad to init (or initWithCoder: if using a storyboard/xib). This way you won't have to call -view.
If I understand right, you want X to be initialised. So you can perform all you initialisation actions on your init constructor. viewDidLoad will only be called by the framework when you perform some presentation, either by pushViewController or addSubview. The reason for that is that because the framework wants to avoid getting instances of views on the memory without being used. So you can initialise all you want from your controllers but the views won't be loaded.