In this current SplitViewController constellation the MasterVC performs an operation/calculation in viewWillAppear. The result of that operation is needed in the DetailVC to load its view properly (the DetailVC has a table view).
I don't know how the loading/appearing sequence in a SplitViewController is (and how reliable it might be if known), but is it possible to
Perform the operation/calculation in the MasterVC on viewWillAppear
Pass the information to the DetailVC (either using the properties of DetailVC or with a protocol)
DetailVC will be loaded when the required information is available (e.g. viewWillLoad/viewWillAppear of DetailVC)?
Both the master and detail viewDidLoad methods are called at start up with a split view controller. So, you can't control when the detail controller gets loaded based on something happening in the master view controller. The detail view controller's viewWillAppear is called before the master's viewWillAppear since you only see the detail view at start up (in portrait orientation). So, you probably need to have a placeholder view in the detail view controller, if you want something to appear there before the master controller does its calculation.
This is only true if the iPad is in portrait orientation when the app starts. If you have it turned to the landscape orientation when you start the app, then you get the viewDidLoad and viewWillAppear of the master before either of those methods gets called in detail.
Related
I am having a multiple UIViewController embedded in a UITabbarController.
These are connected by Relationship Segues.
The starting point, VC1 initially loads data and is then processed to a "detail" view.
Whenever I change tabs and go back to VC1, the application gets stuck, as viewDidLoad is not called.
Is there a way to trigger a function each time VC1 is segued to?
the application gets stuck, as viewDidLoad is not called
The application is not stuck. It is working perfectly. viewDidLoad is called when a view controller is created and loads its view. That only happens once in the life of the view controller. When you leave a view controller and come back to it, it is still there (i.e. it is not being created from scratch), so naturally viewDidLoad is not called.
If your goal is to hear about the fact that the tab bar controller is switching to VC1, give the tab bar controller a delegate and implement tabBarController(_:didSelect:) or similar.
Even better, configure things so that there is no need to do this. If there is common data that is accessed by both view controllers, architect things so that a view controller sends new data up to a data controller and the data controller broadcasts news of the change down to all view controllers that need to know this.
I have a view controller that is a child view controller of my window's root view controller. That child view controller has a table view and when i select a row it tells the parent view controller to present a view controller modally. The modal view controller, however, never appears. I created a bare bones test view controller that just prints viewDidLoad and viewWillAppear. What I notice is that when I call parentVC.present(testVC, animated:true, completion:nil), viewDidLoad is run, but viewWillAppear is not. viewWillAppear is only then called when I interact with the UI in some way. Whether tapping, panning, scrolling or whatever.
I've spent hours trying to debug this. It doesn't seem like the main queue is blocked and I've reduced the problem to its bare bones. The modally presented view controller's viewWillAppear is simply not called until I interact with the UI again.
What could be causing this symptom?
In comments, you mention that you're instantiating your view controller with
let vc = TestVC()
where TestVC is presumably a (largely empty) UIViewController subclass.
A view controller needs a view created either via either storyboard scene (using instantiateViewController), a NIB or, in very rare cases, a view you create in loadView (which you shouldn’t be confused with viewDidLoad).
I’d suggest creating a storyboard scene (assuming you are using storyboards), give it a storyboard ID, and then use instantiateViewController:
let vc = storyboard.instantiateViewController(withIdentifier: "foo")
But just having a UIViewController subclass called TestVC and instantiating it with TestVC() won’t work.
In our discussion, you said you wanted to do this programmatically with no NIB nor storyboard. If so, use loadView. See https://stackoverflow.com/a/37964249/1271826 for an example.
I need a loading screen to show while some data is being downloaded from the server. I present a view controller with modal segue without animation. But I don't know how to dismiss the loading screen view controller since dismissViewController function can only be called from inside.
I should be able to dismiss the loading screen view controller from another view controller. Any suggestions?
One option is using NSNotificationCenter. You can post custom notification and listen it in loading view for closing it.
If you are getting the data in parent view then you can close the loading view from parent view also. You can call dismissViewController from parent view using presentingViewController property of UIViewController class.
In your case from parentView you can dismiss the child view using:
[self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
presentingViewController
The view controller that presented this view controller. (read-only)
Declaration
Swift
var presentingViewController: UIViewController? { get }
Objective-C
#property(nonatomic, readonly) UIViewController *presentingViewController
Discussion
When you present a view controller modally (either explicitly or
implicitly) using the presentViewController:animated:completion:
method, the view controller that was presented has this property set
to the view controller that presented it. If the view controller was
not presented modally, but one of its ancestors was, this property
contains the view controller that presented the ancestor. If neither
the current view controller or any of its ancestors were presented
modally, the value in this property is nil. Import Statement
import UIKit Availability
Available in iOS 5.0 and later.
Do you need to show another VC? You could just show a subview, making it visible=true when you start the app, and on the request success or failure callbacks hide it again (depending on the networking framework you are using)
I don't know were you start the request and were you know when it is done, if the loading screen knows when the download is finished you can do one of two things, or you pass the first VC as a delegate (defining a protocol) to the second VC (loading screen), and when you know on the loading screen that the download is finished you call a method on the delegate that will dismiss the loading screen,
Or you can use NSNotificationCenter, register for some kind of events on the first VC and when the process finishes on the loading screen you notify the first VC with this method, to dismiss the loading screen.
If you start the process on the first VC, and you know when it ends also on the first VC I would not understand your question, as you would just dismiss the loading screen and it would work.
Could you give more info? If you'd like I can post some code in order to help you in one of this approaches.
in the viewDidLoad method i have this code.
When the application is running its not go to the another viewController, its gives me an error:
Warning: Attempt to present <CompleteCountryViewController: 0x7fb971779be0> on <ViewController: 0x7fb97176f3e0> whose view is not in the window hierarchy!
What can i do, that when the application running its will go to another viewController?
You should not present a view controller in the viewDidLoad method of another controller because you cannot show a view controller (present modally or push) when a transition is already occurring (push, pop, present, dismiss).
My suggestion is that you move the code in your code sample to the viewDidAppear: method. At this point, you know for sure that the transition has completed.
You seem to have a slight misunderstanding of the lifecycle of UIViewController if you want to modally present a view controller inside the viewDidLoad of another one.
viewDidLoad gets called in one view controller after it has been instantiated and its view components have been loaded (thus the name). The view of that view controller is about to be displayed, so it doesn't make much sense to instantiate another view controller at this point and present it on the first one.
Let me give you an example with two view controller A and B.
You instantiate A and its viewDidLoad gets called. So, A is about to be displayed! What you are doing in your code now is to instantiate B at this very point and show it on A. iOS doesn't like that and will give you your error.
I had an issue where I was attempting to present a modal view controller within the viewDidLoad method. The solution for me was to move this call to the viewDidAppear: method.
View controller's view is not in the window's view hierarchy at the point that it has been loaded (when the viewDidLoad message is sent), but it is in the window hierarchy after it has been presented (when the viewDidAppear: message is sent).
I have an app that uses a navigation controller. The views display results from picking a ranom card from a deck. The logic of what card was picked and what options to use is determined in the OnCreate of each view.
After I go through the views then I go back to the root view. Now when I go back through the vues, the same information is being shown and oncreate is not being called. It seems like when I go back to the root views, the vues that get popped off memory are not being freed, so it is using the same object. Is this how its suppose to work, or am I doing something wrong so popToRootViewController is not releasing the meory the views where using?
I'm using the following code to go to the next view
if (mGet == nil) {
mGet = [[cGet alloc] initWithNibName:#"cGet" bundle:[NSBundle mainBundle]];
}
You use -viewDidLoad to perform one-time setup of your view controller at the point that all view objects are instantiated. Just before a viewController presents its view, -viewWillAppear: is executed. Just before a viewController's view goes away, -viewWillDisappear: is executed. So when you need to respond to a viewController displaying its view, or going offscreen, override -viewWillAppear: and -viewWillDisappear: in your view controller.
Check the Apple documentation for UIViewController for these details.