What is the use of the contentOffset property in UIScrollView?
It could be considered as the coordinate of the origin of scrollView's frame relative to the origin of its contentView's frame. See the picture below:
According to the documentation, the contentOffset property represents:
The point at which the origin of the
content view is offset from the origin
of the scroll view.
In plain speak, it's how far the view has moved in each direction (vertical and horizontal). You can unpack vertical and horizontal distance by accessing the x and y properties of the CGPoint:
CGFloat xOffset = _myScrollView.contentOffset.x;
CGFloat yOffset = _myScrollView.contentOffset.y;
Here you see two rectangles:
the visible area
the total area
Scrolling is changing the origin of the visible area within the total area.
In iOS all views have a visible area represented by the view.bounds rectangle. The class UIScrollView is a view with an unique property: it has a second rectangle called “content view” with a size bigger than its bounds. Thus, in a scroll view:
the visible area is scrollView.bounds
the total area is called content view, whose size is scrollView.contentSize
contentOffset is another name for scrollView.bounds.origin, implemented as follows:
var contentOffset: CGPoint {
get { return bounds.origin }
set {
var bounds = self.bounds
bounds.origin = newValue
self.bounds = bounds
}
}
When we change the contentOffset programmatically, we are also changing the bounds.origin, which causes a different area of the content view to be rendered. If we animate this change with setContentOffset(pt, animated: true), the scrollView appears to scroll as dragged by the user’s finger.
The official documentation defines contentOffset like this (italics are mine):
contentOffset: The point at which the origin of the content view (the total area) is offset from the origin of the scroll view (the visible area).
I’d like to highlight the comment of #westsider on the accepted answer:
For instance, if you want to present n pages that can be scrolled through, you create a UIScrollView with contentSize (n*pageWidth, pageHeight) and with bounds size (pageWidth, pageHeight). You then set contentOffset.x = (n-1) * pageWidth with n = 1 to display the first page.
Related
This code is only working with fix height and width. How can Round UIImageView when we use multiplier?
Here, is the code that Circle my ImageView. Width and Height is 300.
class MusicViewController: UIViewController {
#IBOutlet weak var imgAlbum: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
imgAlbum.layer.borderWidth = 1
imgAlbum.layer.masksToBounds = false
imgAlbum.layer.borderColor = UIColor.black.cgColor
imgAlbum.layer.cornerRadius = imgAlbum.frame.height/2
imgAlbum.clipsToBounds = true
}
}
If I change my height and width to multiplier like. Now, the multiplier of Height 0.5 and width 0.8.
(Proportional height and width to SuperView)
As #RajaKishan and #aiwiguna both said that you can't get a square image with both proportional height and width constraint together because then you can not get a round circle with different height and width.
You can set width or height proportional to superview and set the aspect ratio to 1:1 then you can change the multiplier and get the circle properly. You can check to attached image for constraints
then set cornerRadius in viewDidLayoutSubviews(), not in viewDidLoad(). (viewDidLoad() is called before the layout constraints change the view height, and only once. viewDidLayoutSubviews() is called any time your view's geometry changes, so you should invoke any layout logic there.
override func viewDidLayoutSubviews() {
self.yourImageView.layer.cornerRadius = self.yourImageView.bounds.height/2
self.yourImageView.clipsToBounds = true
}
you will not get a square by using proportional width and proportional height constraint together like that, in different device it will have different height and width
my suggestion is to use only one proportional width or proportional height (which one you want) and use aspect ratio constraint 1:1 on the view
(Xcode 11, Swift)
Being a newbie to iOS and Autolayout, I'm struggling with implementing a fairly simple (IMHO) view which displays a [vertical] list of items. The only problem is that items are decided dynamically and each of them could be either text or image (where either of those could be fairly large so scrolling would be required). WebView is not an option, so it has to be implemented natively.
This is how I understand the process:
Make in IB a UIScrollView and size it to the size of the outer frame.
Make a container view as a subview of UIScrollView (again, in IB) and size it the same.
Set constraint on equal width of both
At runtime, populate container view with UILabels/UIImageViews and also set constraints programmatically to ensure proper layout.
"Tell" scrollview about the subview height in order to make it manage the scrolling thereof.
Is this the right approach? It doesn't seem to work for me (for a toy example of dynamically adding a very tall image to a container view - I cannot get the scrolling to work). What would be the proper way to do the last step in the process above - just force the contentSize of the scrollview to the size of the populated container view (it doesn't seem to work for me). Any help would be appreciated.
When adding multiple elements to a scroll view at run-time, you may find it much easier to use a UIStackView... when setup properly, it will automatically grow in height with each added object.
As a simple example...
1) Start by adding a UIScrollView (I gave it a blue background to make it easier to see). Constrain it to Zero on all 4 sides:
Note that we see the "red circle" indicating missing / conflicting constraints. Ignore that for now.
2) Add a UIView as a "content view" to the scroll view (I gave it a systemYellow background to make it easier to see). Constrain it to Zero on all 4 sides to the Content Layout Guide -- this will (eventually) define the scroll view's content size. Also constrain it equal width and equal height to the Frame Layout Guide:
Important Step: Select the Height constraint, and in the Size Inspector pane select the Placeholder - Remove at build time checkbox. This will satisfy auto-layout in IB during design time, but will allow the height of that view to shrink / grow as necessary.
3) Add a Vertical UIStackView to the "content view". Constrain it to Zero on all 4 sides. Configure its properties to Fill / Fill / 8 (as shown below):
4) Add an #IBOutlet connection to the stack view in your view controller class. Now, at run-time, as you add UI elements to the stack view, all of your "scrollability" will be handled by auto-layout.
Here is an example class:
class DynaScrollViewController: UIViewController {
#IBOutlet var theStackView: UIStackView!
override func viewDidLoad() {
super.viewDidLoad()
// local var so we can reuse it
var theLabel = UILabel()
var theImageView = UIImageView()
// create a new label
theLabel = UILabel()
// this gets set to false when the label is added to a stack view,
// but good to get in the habit of setting it
theLabel.translatesAutoresizingMaskIntoConstraints = false
// multi-line
theLabel.numberOfLines = 0
// cyan background to make it easy to see
theLabel.backgroundColor = .cyan
// add 9 lines of text to the label
theLabel.text = (1...9).map({ "Line \($0)" }).joined(separator: "\n")
// add it to the stack view
theStackView.addArrangedSubview(theLabel)
// add another label
theLabel = UILabel()
// multi-line
theLabel.numberOfLines = 0
// yellow background to make it easy to see
theLabel.backgroundColor = .yellow
// add 5 lines of text to the label
theLabel.text = (1...5).map({ "Line \($0)" }).joined(separator: "\n")
// add it to the stack view
theStackView.addArrangedSubview(theLabel)
// create a new UIImageView
theImageView = UIImageView()
// this gets set to false when the label is added to a stack view,
// but good to get in the habit of setting it
theImageView.translatesAutoresizingMaskIntoConstraints = false
// load an image for it - I have one named background
if let img = UIImage(named: "background") {
theImageView.image = img
}
// let's give the image view a 4:3 width:height ratio
theImageView.widthAnchor.constraint(equalTo: theImageView.heightAnchor, multiplier: 4.0/3.0).isActive = true
// add it to the stack view
theStackView.addArrangedSubview(theImageView)
// add another label
theLabel = UILabel()
// multi-line
theLabel.numberOfLines = 0
// yellow background to make it easy to see
theLabel.backgroundColor = .green
// add 2 lines of text to the label
theLabel.text = (1...2).map({ "Line \($0)" }).joined(separator: "\n")
// add it to the stack view
theStackView.addArrangedSubview(theLabel)
// add another UIImageView
theImageView = UIImageView()
// this gets set to false when the label is added to a stack view,
// but good to get in the habit of setting it
theImageView.translatesAutoresizingMaskIntoConstraints = false
// load a different image for it - I have one named AquariumBG
if let img = UIImage(named: "AquariumBG") {
theImageView.image = img
}
// let's give this image view a 1:1 width:height ratio
theImageView.heightAnchor.constraint(equalTo: theImageView.widthAnchor, multiplier: 1.0).isActive = true
// add it to the stack view
theStackView.addArrangedSubview(theImageView)
}
}
If the steps have been followed, you should get this output:
and, after scrolling to the bottom:
Alignment constraints (leading/trailing/top/bottom)
The alignment constraint between Scroll View and Content View defines the scrollable range of the content. For example,
If scrollView.bottom = contentView.bottom, it means Scroll View is
scrollable to the bottom of Content View.
If scrollView.bottom = contentView.bottom + 100, the scrollable
bottom end of Scroll View will exceed the end of Content View by 100
points.
If scrollView.bottom = contentView.bottom — 100, the bottom of
Content View will not be reached even the scrollView is scrolled to
the bottom end.
That is, the (bottom) anchor on Scroll View indicates the (bottom) edge of the outer frame, i.e., the visible part of Content View; the (bottom) anchor on Content View refers to the edge of the actual content, which will be hidden if not scrolled to.
Unlike normal use cases, alignment constraints between Scroll View and Content View have nothing to do with the actual size of Content View. They affect only “scrollable range of content view” but NOT “actual content size”. The actual size of Content View must be additionally defined.
Size constraints (width/height)
To actually size Content View, we may set the size of Content View to a specific length, like width/height of 500. If the width/height exceeds the width/height of Scroll View, there will be a scrollbar for users to scroll.
However, a more common case will be, we want Content View to have the same width (or height) as Scroll View. In this case, we will have
contentView.width = scrollView.width
The width of Content View refers to the actual full width of content. On the other hand, the width of Scroll View refers to the outer container frame width of Scroll View. Of course, it doesn’t have to be the same width, but can be other forms like a * scrollView.width + b.
And if we have Content View higher (or wider) than Scroll View, a scrollbar appears.
Content View can not only be a single view, but also multiple views, as long as they are appropriately constrained using alignment and size constraints to Scroll View.
For details, you may follow this article: Link.
I have the following subview that I would like to centered in horizontally on the screen and set the vertical distance manually.
let customImageView = AnimationView(name: "image")
customImageView.frame = CGRect(x: -140, y: 40, width: 700, height: 700)
customImageView.contentMode = .scaleAspectFill
self.view.addSubview(customImageView)
Is it possible to ensure that the vertical distance set will account if the screen size of the phone is smaller.
This sounds like a job for Auto Layout (https://developer.apple.com/library/archive/documentation/UserExperience/Conceptual/AutolayoutPG/index.html), which is Apple's constraint-based system made specifically to dynamically size views in relation to other views and screen sizes. In your case, you could set a greater than/less than to constraint to the top of the view and your subview, so that it will be at least a certain amount of spacing with the option to grow if the screen is larger/smaller.
If you would like to still do frame based layouts (e.g. creating a CGRect/frame), you'll have to do the math yourself based on the view.frame.size.height value. Be aware that a view controller's view frame might not be set before viewDidLayoutSubviews is called.
The UIButton in the scrollView is visible, but not accessible. I am using Constraints.
My UI structure is this:
- UIView
- scrollView: UIScrollView
- contentView: UIView
- UIButton
- UIButton
- UIButton
- ....
- UIButton
I've already tried to set the contentSize of the scrollView. And the height of the contentView. Next to that I've tried to uncheck the checkbox Adjust Scroll View Insets in the storyboard of that ViewController without any luck. I've also set the priority of the Align Center Y to 250, and the priority bottom space to 250 of the contentView.
func updateScrollViewSize() {
var contentRect = CGRect.zero
for view in contentView.subviews {
contentRect = contentRect.union(view.frame)
}
contentRect.size = CGSize(width: scrollView.contentSize.width, height: contentRect.height + 50)
scrollView.contentSize = contentRect.size
contentView.frame.size = contentRect.size
contentView.layoutIfNeeded()
}
The button I try to reach has a Y value of: 1030.0
The height of the contentView is: 871.0
Step-by-step:
Add a scroll view to your view, background color red, constrain it 20-pts on each side:
Add a UIView as your "content view" to the scroll view (green background to make it easy to see), constrain it 0-pts on each side, constrain equal width and equal height to the scroll view. Important: change the Priority of the Height constraint to 250!
Add a UILabel to the contentView, constrain it 30-pts from the top, centered horizontally:
Add another label to the contentView, constrain it 300-pts from the first label, centered horizontally:
Add a UIButton to the contentView, constrain it 30-pts from the bottom, centered horizontally:
Now add a vertical constraint from the bottom of the second label to the top of the button, and set it to 400-pts:
As you see, this pushes the button off-screen past the bottom of the scroll view.
Run the app. You will be able to scroll down to see the button, and you'll be able to tap it.
Absolutely no code needed!
If you use AutoLayout, you don't needed to install frames manually.
You can try install constraints properly and content size will be right in this case and you won't have to install content size manually.
If you achieve this, I guess everything will work correctly.
You can follow this or this guide
I am using AutoLayout. I have a view with %10 width and 200 fixed height. I placed a UILabel into that view with 0 margins. Then I am rotating the UILabel, changing the content and calling sizeToFit() function. At the load of the controller the rotation works but the content is being truncated. After I did a button click on the controller, the UILabel is being enlarged and content is being fit.
What should I do to avoid this problem?
Note: I checked the width and height of the label's frame with debugging. After sizeToFit() the width and height of the frame changes as expected. However, the UI is not refreshing. I also tried label.setNeedsLayout() and label.layoutIfNeeded() but nothing changed.
For rotation I am using below extension:
extension UILabel {
#IBInspectable
var rotation: Int {
get {
return 0
} set {
let radians = CGFloat(CGFloat(Double.pi) * CGFloat(newValue) / CGFloat(180.0))
self.transform = CGAffineTransform(rotationAngle: radians)
}
}
}
You can try view.layoutIfNeeded() instead of label.layoutIfNeeded()