Recently I wrote an app with one single scene and ViewController. I had to set a custom background picture for the View, which the ViewController manages (i.e. my top view contained the UIImageView). Later on I had to implement some logic in ViewController, so that it properly rotates/changes the picture when the screen is rotated. Also I had to overwrite some properties like preferredStatusBarStyle for the ViewController.
Now I have to implement a couple more scenes / screens in my app and it turns out that they all must have the same design as this currently present screen, so I think it makes sense if I create a CommonViewController which contains this common rotation-related logic for background picture, so that I can inherit all my other ViewControllers from this CommonViewController. The only problem I have is that CommonViewController "requires" that the view it manages has a backgroundPicture: UIView property, which I don't know how to ensure.
If I create a new file CommonViewController together with XIB-file, I can add the backgroundPicture image view in XIB and connect it with code (via regular "control-drag" approach), but apparently this won't work, as there is no guarantee that the views which inherit CommonViewController will have this property. What is the correct way to solve this issue without hacks on iOS in Swift?
Unfortunately I could not find a solution, maybe I've been searching for something wrong. It seems that I somehow need to inherit a CommonViewController for each scene (for each CustomViewController), but also I have to somehow set the top view of each of these controller's to be equal to some CommonView, so that CommonViewController does not crash when I try to access #IBOutlet weak var backgroundPicutre: UIImageView!.
The obvious way would be to define some method or property in the CommonViewController, so that the controllers which inherit it, can implement / override it, but it seems a bit hacky as it still requires copy-pasting in each ViewController which inherits CommonViewController.
How I imagined the solution: I create CustomViewController: CommonViewController, then I create a view controller in my Storyboard and change the "Class" property to "CustomViewController" (in property editor), then I select the view which corresponds to this newly added controller and change the "Class" property to "BackgroundImageView. But I'm not sure if it's the correct way to do (also I doubt thatCustomViewControllerwill properly "connect" itsIBOutletfieldbakcgroundImageViewwith the correspondingUIViewfromBackgroundImageView`, that's why I wanted to ask experts what they think about it.
I think you should define your base controller (CommonViewController) entirely in code, i.e. don't use no xibs / storyboards for the base controller. It doesn't mean you should rid off storyboards / xibs completely. Interface for alll other view controllers except CommonViewController may still be implemented with xibs / storyboards.
In this case CommonViewController implementation may look like this:
import UIKit
class CommonViewController: UIViewController {
// use this property every time you need to
// manipulate backgroundPicture
var backgroundPicture: UIImageView = {
// Replace with your image name
let image = UIImage(named: "BackgroundPicture")!
let imageView = UIImageView()
imageView.image = image
return imageView
}()
override func viewDidLoad() {
// If subclass overrides viewDidLoad()
// it should contain super.viewDidLoad()
super.viewDidLoad()
view.addSubview(backgroundPicture)
// Align backgroundPicture to bounds of superview
// You can remove this code and implement
// your own alignment with frames or Autolayout
backgroundPicture.frame = view.bounds
// Send backgroundPicture to back of the view
// Otherwise backgroundPicture may overlap views added in subclasses
view.sendSubviewToBack(backgroundPicture)
}
override func viewDidLayoutSubviews() {
// If subclass overrides viewDidLayoutSubviews()
// It should contain super.viewDidLayoutSubviews()
super.viewDidLayoutSubvews()
// Align backgroundPicture to bounds of superview
// You can remove this code and implement
// your own alignment with frames or Autolayout
backgroundPicture.frame = view.bounds
}
}
Related
In a couple of my projects I think I'm not created a great structure in many cases.
It could be a game where I've created a game board (think about chess) with a grid of 8 * 8 cells. Each cell has a gesture recognizer that relies on a subclass (cell.swift), with the game logic in a parent ViewController.
For arguments sake, let us say we want to display to the user which square they have touched.
I've found out how to do this from the subclassed UIView (obvs. create the alert in the subclassed UIView / cell.swift in this example)
UIApplication.shared.keyWindow?.rootViewController?.present(alertController, animated: true, completion: nil)
but it seems to break the structure of the app - but wouldn't it be the same accessing an action in the parent ViewController? What is the best way of approaching this>
Your rootViewController is the VC on the bottom of your stack. It's not a safe way to access the visible VC, and is rarely useful, in general (there are cases, but I doubt your app would find them useful).
What you likely want to use is a delegate pattern. Let's say the parent VC that displays your chess board (let's call this MyBoardViewController), conforms to a protocol like the following. MyView is whatever custom UIView class you're using for the chess squares:
protocol SquareAlertHandler {
func handleSquarePressed(sender : myView)
}
And add the following property to your MyView class:
weak var delegate : SquareAlertHandler?
And replace whatever event handler you're currently using, with the following (I'm assuming you're using a UIButton in IB to handle the press, and have arbitrarily named the outlet 'didPress:'):
#IBAction didPress(sender : UIButton) {
delegate?.handleSquarePressed(self)
}
Now, add the protocol to your MyBoardViewController, and define the method:
class MyBoardViewController : UIViewController, SquareAlertHandler {
... ... ...
func handleSquarePressed(sender : myView) {
// Do something to handle the press, here, like alert the user
}
... ... ...
}
And finally, wherever you create the MyView instances, assign the MyBoardViewController instance as the delegate, and you're good to go.
Depending on your Swift literacy, this may be confusing. Adding code, so that I can at least match up the class names, would help to clarify things.
I would like to create multiple UIViews that can be reproduced by using a single function. I have a UIView that is placed on a storyboard and connected to my class with an IBOutlet:
#IBOutlet weak var contentView: UIView!
I have a function that loads a xib into my UIView:
func createView(layoutConstant: CGFloat) {
if let customView = NSBundle.mainBundle().loadNibNamed("TestView", owner: self, options: nil).first as? TestView {
contentViewTopLayoutConstraint.constant = layoutConstant
contentView.addSubview(customView)
}
}
I am now trying to add two of them to my view, but only one shows up:
createView(0)
createView(70)
Any ideas?
I think both views are added, although they happen to be in the same spot, so it looks like there is only one! A quick and dirty way to verify that would be updating your createView method with this line:
contentView.frame.origin.y = layoutConstant
Basically your contentViewTopLayoutConstraint is not connected to the views you are creating, so setting its constant value will not have any impact.
Because frames for all those views will of same size. Origin(x,y) will be same for all the views, so they are overlapping one on another and you can only see the top one view.
In your code example it looks like you're only setting a layout constraint on the contentView you are placing your two new views inside of. What you need to do is set layout constraints on the two views your are placing inside in relation to their superview i.e. the contentView.
Basically, add the layout constraints to the customView views.
its quite simple.. iterate a loop by creating uiview along with adding those into the array and customize your particular view by getting them using array index.
Happy code ..
I'm using PNChart in a UIView and overtime my method runs it adds an addition line to the graph rather than recreating the entire graph. How do I clear a UIView, before add[ing]Subview?
#IBOutlet weak var lineChart: UIView!
...
// in function
theLineChart.chartData = [actualData]
theLineChart.strokeChart()
// want to clear self.lineChart here
self.lineChart.addSubview(theLineChart)
If by “clear” you mean remove all previously added subviews from it, you could try something like:
while let subview = lineChart.subviews.last {
subview.removeFromSuperview()
}
The caveat is that lineChart should remain a plain UIView (or your self-made subclass that you know the implementation of), as otherwise it may have internal subviews that you shouldn't remove.
Then again, if it is nothing but a plain UIView, you could simply replace the whole view with a new one (this might even make it simple to cross-fade between old and new views if such is desired).
I'm writing an app that should present overlays in specific situations, like for example the lack of location services enabled for the app.
Overlay is a UIView with a UIImageView (background) a UILabel (title) and a UIButton calling a specific action. I want to use Interface Builder to set up the overlay UI but I would like to recall the overlay and show it on different UIViewControllers, depending on when the lack of location services is detected.
I have set up a custom class (subclass of UIView) to link a xib file. Code below:
class LaunchCustomScreen: UIView
{
#IBOutlet var title: UILabel!
#IBOutlet var enableLocationButton: UIButton!
#IBOutlet var waitingIndicator: UIActivityIndicatorView!
#IBOutlet var bckgroundImage: UIImageView!
func setupDefault()
{
title.text = "Location Services Required"
enableLocationButton.setTitle("Enable Location Services", forState: UIControlState.Normal)
enableLocationButton.addTarget(self,
action: "promptUserForLocation",
forControlEvents: UIControlEvents.TouchUpInside)
hideLocButton()
}
func hideLocButton()
{
enableLocationButton.hidden = true
}
func showLocButton()
{
enableLocationButton.hidden = false
}
}
Then I have created the xib file which is of Class LaunchCustomScreen and I linked the IBOutlets to all the objects in it (UILabels, UIBUtton, UIImageView)
Then I have set some global functions to be called from any other UIViewController in order to show/hide the overlay on the specific view controller and configure it with UIButton hidden or visible (it will be hidden with a waiting indicator when user location is still loading). Below related code:
func setupLaunchDefault(vc: UIViewController) -> LaunchCustomScreen
{
for aSubview in vc.view.subviews
{
if aSubview.isKindOfClass(LaunchCustomScreen)
{
NSLog("Found already a launch screen. Removing")
aSubview.removeFromSuperview()
}
}
var screen: LaunchCustomScreen = LaunchCustomScreen()
screen.setupDefault()
return screen
}
func showLaunchAskLocation(vc:UIViewController)
{
var screen = setupLaunchDefault(vc)
screen.bounds = vc.view.bounds
screen.showLocButton()
vc.view.addSubview(screen)
}
Now I'm trying if the solution works and it crashes on the setupLaunchDefault function. Reason is that even if an instance of LaunchCustomSCreen is created, the variables (title, enableLocationButton) are still nil. I though they should be non-nil thanks to the IBOutlet to the xib... what am I missing?
Thank you in advance for your help!
I have set up a custom class (subclass of UIView) to link a xib file
No, you haven't. No such "link" is possible.
what am I missing?
You're not missing anything, because you've already figured it out!
Merely creating a LaunchCustomScreen instance out of thin air (i.e. by saying LaunchCustomScreen(), as you are doing) merely creates an instance of this class. It has nothing whatever to do with the .xib (nib) file! There is no magic "link" whatever between the class and the nib! Thus, nothing happens that would cause these properties to get any value. They are, as you have rightly explained, nil.
You have designed and configured one special particular instance of LaunchCustomScreen in the nib. That is the instance whose outlets are hooked up, within the same nib. So if you want an instance of LaunchCustomScreen with hooked-up outlets, you must load the nib! Loading the nib is exactly equivalent to making an instance of what's in the nib - it is a form of instantiation. And here, it's the form of instantiation you want, because this instance is the instance you want.
So, the answer is: do not say LaunchCustomScreen() to get your LaunchCustomScreen instance (screen). Instead, load the nib to get your LaunchCustomScreen instance - and all will be well.
So, let's say your .xib file is called LaunchCustomScreen.xib. You would say:
let arr = NSBundle.mainBundle().loadNibNamed("LaunchCustomScreen", owner: nil, options: nil)
let screen = arr[0] as UIView
The first result, arr, is an array of top-level objects instantiated from the nib. The first of those objects (probably the only member of the array) is the view you are after! So you cast it to a UIView and you are ready to stick it into your interface. Since the view comes from the nib, its outlets are set, which is what you're after. You can do this as many times as you need to, to get as many "copies" of this view as you like.
I have a UIViewController (let's call it "EditViewController") which has a Container View on it (call it "ContainerView") where I switch in and out various subviews (call the one I'm most concerned with "EditDetailsView").
From the EditDetailsView I need to change the title in the navigation bar of the EditViewController. I can't seem to be able to figure out how to reference it.
From inside EditViewController I can simply make a statement like:
self.title = #"Some new title";
and it changes just fine.
But from the EditDetailsView view that is currently the subview of ContainerView nothing seems to work:
self.title = ... is obviously wrong.
super.title = ... doesn't work and seems wrong anyway.
super.super.title = ... errors out as super is not a property found on UIViewController.
Can someone please tell me how to reference the title? I'm kinda lost.
Thanks!
While digging through the parentViewController chain is possible, it is error prone and unrecommended. It is considered a bad design. Imagine you set up your view controller hierarchy in some manner, but after a few months change it a bit and now there is one level deeper. Or, you would like to use the same view controller in several different scenarios. A much better design would be to pass the new title to the container view controller using delegation. Create a delegate protocol, with a method for setting the title.
- (void)childViewController:(ChildViewController*)cvc didChangeToTitle:(NSString*)title;
I know this is an old thread, but in case someone else needs it: to avoid boilerplate code with delegation, and avoid digging into the parentViewController, I did it the other way around.
I've referenced the child view controller from the parent and got their title. So no matter which child you show, you will always get the right title.
This is in Swift 3.
So, basically, this is your parent:
class EditViewController: UIViewController {
override func viewDidLoad() {
if let child = self.childViewControllers.first {
self.title = child.title
}
}
}
And this is your child:
class ContainerView: UIViewController {
override func viewDidLoad() {
self.title = "Sbrubbles"
}
}
Another good way to avoid excess code with delegation is to use RxSwift, if you are familiar to Reactive programming.