I am attempting to learn Apple's Swift. I was recently trying to build a GUI app, but I have a question:
How do I interact with GUI elements of my app? For instance, I used interface builder to make a UILabel, and I connected it to my viewcontroller by control-clicking, so that I get the #IBOUTLET thing. Now, how do I, while in my view controller, edit the text of this UILabel? To state it another way, what code can I use to programatically control the text of something on my storyboard? All methods I have found online only appear to work with a button generated in code, not a button generated on a storyboard.
I've seen code like
self.simpleLabel.text = "message"
If this is right, how do I link it with the label in question? In other words, how do I adapt this code to be connected with the IBOutlet (If that's what I do)
If you've successfully linked the control with an IBOutlet on your UIViewController class, then the property is added to it and you would simply replace simpleLabel with whatever you named your IBOutlet connection to be like so:
class MyViewController: UIViewController {
#IBOutlet weak var myLabel: UILabel!
func someFunction() {
self.myLabel.text = "text"
}
}
The outlet you created must've been named by you. The outlet belongs to your view controller. self.simpleLabel means 'fetch the value of my property named 'simpleLabel'.
Since different outlets have different names, using self.simpleLabel here won't work until your outlet is named 'simpleLabel'. Try replacing 'simpleLabel' with the name you gave to the outlet when you created it.
The correct way now would be:
self.yourLabelName.text = "message"
If you have something like this for an IBOutlet:
#IBOutlet var someLabel: UILabel!
then you could set the text property just like in your example:
someLabel.text = "Whatever text"
If you're having problems with this, perhaps you're not assigning the text property in the right place. If it's in a function that doesn't get called, that line won't execute, and the text property won't change. Try overriding the viewDidLoad function, and put the line in there, like this:
override func viewDidLoad() {
super.viewDidLoad()
someLabel.text = "Whatever text"
}
Then, as soon as the view loads, you'll set the text property. If you're not sure if a line of code is executing or not, you can always put a breakpoint there, or add some output. Something like
println("Checkpoint")
inside a block of code you're unsure about could really help you see when and if it runs.
Hope this helps.
You may trying to change a UI component not in the main thread, in that case, do this:
DispatchQueue.main.async {
someLabel.text = "Whatever text"
}
Related
Now I'm learning swift using Xcode, but I don't know where to drag and drop and why drag and drop "label" to somewhere
should I drop no.1? or no.2? or no.3? and why I should drop there?
If you drop it to 1, Xcode automatically generate an #IBOutlet for you. If you drop it to 2 or 3, then #IBAction. There's no other reason for that except that Xcode tries to be smart and help you organize code more nicely: properties with properties in the top of the class, methods – in the methods area. And you can also move declarations to another place later: except for code style matters, it doesn't matter, where exactly within your class you put declarations.
as you are trying to take an IBOutlet for a label , its nice to keep it on top of the class (where you mention 1).
normally Xcode gives suggestion you , if you drug on top side it will be #IBOutlet
or you on bottom like 2 or 3 it will be #IBAction like you already took a button action in your code .
Your Solution On Code:
import UIKit
class CodePresentViewController: UIViewController {
#IBOutlet weak var YourLabel: UILabel! // insert #IBOutlet type property here
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func tapBackButton(_ sender: UIButton) {
//Yout Button COde
}
}
If you want to own the label in your code, and then make some configuration to the label by code, use "1". It will give you a #IBOutlet label object in your code.
If you want to set the label's action, use "2" or "3".
Let's say I have created a UI with some views using an interface builder (not in code, so not programmatically).
How can I assign human readable ids / tags to these views, so that I could reference them in code?
I know that I can assign an integer tag to a view using attribute inspector and then make a dictionary (or enum) to store the mapping of tags to the views. However, this is an error-prone method which also scales really badly (imaging assigning integer tags to hundred of views in a complex app...).
Is there a better solution for this problem? Is there a way to directly assign a human readable tag / id to a view, like "resumeButton"?
UPDATE:
Here is an example scenario of what I want to achieve:
UI with five different buttons; the buttons have image and no title
all five buttons are connected to the same IBAction in code
in IBAction I have a switch statement, so that depending on which button is clicked, different versions of code are executed
UPDATE 2:
SOLUTION
I ended up implementing a simple custom view:
#IBDesignable
class CustomButton: UIButton {
#IBInspectable var stringTag: String = defaultID
}
This way I can see an additional property stringTag in Interface Builder and can simply add a value to it directly in Interface Builder.
You could create an extension property on UIView to store an identifier string. If you made that extension property IBInspectable, you could set and view it from the storyboard directly.
More detail on setting up such a property in this answer:
https://stackoverflow.com/a/37166043/1830999
The built-in tag property for UIView is just an integer, so it isn't very descriptive for humans who read it.
From what you're describing sounds to me that you are looking for an: Outlets
You are right about tags. Every connection with Interface Builder should be handled using IBAction and IBOutlet.
Since you say that every button has a different action, the simplest solution is to create a separate IBAction for each of them:
#IBAction private func onResumeButtonTapped() {
...
}
#IBAction private func onPauseButtonTapped() {
...
}
If you, for some reason, want to keep them connected to one function, you can use outlets:
#IBOutlet private var resumeButton: UIButton!
#IBOutlet private var pauseButton: UIButton!
#IBAction private func onButtonPressed(_ sender: UIButton) {
switch sender {
case resumeButton:
...
case pauseButton:
...
default:
break
}
}
I have an app I am working on where it shows a balance for users that changes. I would like to display these values as they change and the only way I know how to do that would be with a button. But the values often change on a different view controller so I was wondering if I can set labels equal to a variable that update along with those variables.
Since the values change outside of the view controllers with the labels, the normal way I change labels, using a button, does not apply.
Thanks in advance!
As a general solution, you could achieve this by declaring a property observer in your view controller, example:
class ViewController: UIViewController {
var updatedData = "" {
didSet {
lblData.text = "Data: \(updatedData)"
}
}
#IBOutlet weak var lblData: UILabel!
}
At this point, each time updatedData value is edited, the lblData label text will be updated.
Note that there is also willSet option which is called just before the value is stored, for more information, you could check Swift Properties Documentation - Property Observers.
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 made these (marked with red border) IBOutlets using ctrl + drag
But i don't like to have the exact same line 9 times (DRY)
How do i put these IBOutlets in an Array?
you can define a generic outlet collection in Swift like this:
#IBOutlet var collectionOfViews: Array<UIView>? // = [UIView]?
or for e.g. UIButton objects:
#IBOutlet var collectionOfButtons: Array<UIButton>? // = [UIButton]?
you can find your collections under the Outlet Collections group as usually are in the File's Owner:
it would look on my console after connecting 5 random buttons:
Follow these steps to create an array of outlets an connect it with IB Elements:
Create an array of IBOutlets
Add multiple UIElements (Views) in your Storyboard ViewController interface
Select ViewController (In storyboard) and open connection inspector
There is option 'Outlet Collections' in connection inspector (You will see an array of outlets there)
Connect if with your interface elements
-
class ViewController2: UIViewController {
#IBOutlet var collection:[UIView]!
override func viewDidLoad() {
super.viewDidLoad()
}
}
Solution here Swift - IBOutletCollection equivalent
#IBOutlet var objectCollection: [Object]
This is for macOS (should be similar for iOS) and I do not find an "Outlet Collections" in my storyboard (looks like they took that option out). So I put all my buttons in an NSStackView and linked the stack from storyboard
#IBOutlet weak var buttons: NSStackView!
and then I looped over them to make changes accordingly
for case let (index, button as NSButton) in buttons.arrangedSubviews.enumerated() {
if(index + 1 != someButtonIndex) {button.state = .off}
else {button.state = .on}
}
you can also use tag instead of index
Start with the two view pane where you see both your code and the storyboard. When you make your first IBOutlet connection from the UI to your code, just look carefully at the Connection drop down field and select the option called "Outlet Collection". This will automatically create an array of IBOutlets. Next just look for the little black circle within a circle that is placed in your code where the array is created. Just drag from this circle to all the other UI objects you want to connect to that same collection (not sure if you can mix types). Similarly you can connect all the objects to one Action by dragging from the first black dot created to all the other objects you want to wire up to that action. Also consider EnumerateSequence() to help in working with this Collection. Sweet right?