Combine is one of the new frameworks released during WWDC It provides a declarative Swift API for processing values over time. Today we will talk about one of the hidden features of SwiftUI views, which is onReceive modifier. It allows views to subscribe and react as soon as the publisher emits the value. Usually, we have a data layer that is responsible for all operations in the app, like fetching or saving, and this is the place where all asynchronous operations take place.
But sometimes it is very handy to receive some system-wide notifications in the view layer. An excellent example of this type of notifications can be keyboardWillShowNotification.
Framework emits this notification as soon as the system keyboard appears. By listening to this notification, we can understand when to add some bottom padding to the root view to keep it visible above the keyboard.
As you can see in the example above, the Combine framework provides an extension for the Notification Centerwhich allows us to receive and handle events in a reactive style. SwiftUI views provide the onReceive modifier, which has two arguments: the Publisher from Combine framework and the closure. SwiftUI subscribes to the publisher and runs passed closure whenever the publisher emits the value.
In the example above, we ask SwiftUI to update the state with the value emitted by the publisher, and as soon as state changes, SwiftUI updates our view with a new bottom padding value, which keeps our view above the keyboard.
We can extract this piece of code into a ViewModifier to make it more reusable. Another good example of handling system-wide notifications can be userDidTakeScreenshotNotification. Framework emits this notification as soon the user takes a screenshot of your app. Assume that we are working on the shopping app where we have a product details screen, and we can present a share sheet as soon as the user takes the screenshot of the product.
Here we have another excellent example of using the Combine framework in SwiftUI views to present a share sheet as soon as the user takes a screenshot. Combine framework is a great way to model your data processing, but today we learned about another interesting usage of publishers in combination with SwiftUI views. I hope you enjoy the post. Feel free to follow me on Twitter and ask your questions related to this post.
Thanks for reading, and see you next week!
Merge NotificationCenter.They give you a pre-made list of points, you plug them into into some code, and then you end up with a neat little badge.
This is cool, but what did I even do? Why did we need Geometry Reader? How did I get the rounded edges on the hexagon? For a Pathyou have access to the following methods:. If you really get down to it, you can think of a Path a just a sequence of Curves and Lines. This is starting to make sense.
It looks a little something like this:. The outline is like a rounded rectangle outline with a notch. This is a start. But now how do I add that notch? Trying to draw anything inside the rectangle does nothing. Maybe instead of trying to draw this out as one complex shape, I could just draw this as 2 shapes. We could have the border, and we can have a screen. Reading the API docs, it sounds like you can wrap the paths up into a shape. There still could be some better sizing going on here, but this looks better than I expected.
If you want to check out this code, I have this as well as some animations added in this project on Github. Like this: Like Loading Tags: Path SwiftUI.However, there are times many timeswhen we require more control over the layout of our custom views. For these moments, we have several tools. The first one we are going to explore is GeometryReader. When coding your custom view, you often do not need to worry about surroundings or sizing.
Basic SwiftUI Graphics Drawing
For example, if you need to create a view that draws a rectangle, you just draw a rectangle. It will be drawn with the size and position intended by the parent. It first puts the Text on the top and then the remaining space is passed to MyRectangle.
This view is very obedient and paints in blue exactly what has been given. Not a pixel more, not a pixel less:. As you can see, the view MyRectangle does not worry about size. It only does one job, draw a rectangle. Let SwiftUI figure out where and how big the parent wants it. In this case, the containing VStack is such parent. In many cases, this would be enough.
However, as explained on sessionparents suggest a size and position, but it is up to the child view to decide where and how to draw itself. If the child view is not happy with what its was offered, then he can just ignore it. For example, if you want your custom view to draw a rectangle with half the size of the one suggested by your parent, and if you want to positioned it 5 points to the right edge of the suggested location, then so be it.
Nobody will tell you otherwise. So how do we go off script here? It turns out, is not that complicated. Here is where GeometryReader comes to the rescue. But what does this mean anyway?
Well basically, GeometryReader is yet another view! Almost everything is a view with SwiftUI! As you will see in the example below, GeometryReader lets YOU define its contents, but unlike other views, you also have access to some useful information you can seize to do your thing in the process. Now that we have GeometryReader, it is very simple:. When looking carefully to the example above, you will see a closure variable named geometry.
This is a variable of type GeometryProxy.The goal of this chapter is to introduce SwiftUI 2D drawing techniques. In addition to a group of built-in shape and gradient drawing options, SwiftUI also allows custom drawing to be performed by creating entirely new views that conform to the Shape and Path protocols.
Paths in SwiftUI
SwiftUI includes a set of five pre-defined shapes that conform to the Shape protocol which can be used to draw circles, rectangles, rounded rectangles and ellipses. Within the DrawDemo project, open the ContentView. By default, a shape will occupy all the space available to it within the containing view and will be filled with the foreground color of the parent view by default this will be black. Within the preview canvas, a black rectangle will fill the entire safe area of the screen.
By default, a stroked shape will be drawn using the default foreground color which may be altered using the foregroundColor modifier. Remaining in the ContentView. A Capsule contained in a square frame simply draws a circle.
The above capsule declaration appears as follows when rendered:. The stroke modifier also supports different style types using a StrokeStyle instance. The following declaration, for example, draws a rounded rectangle using a dashed line:.
By providing additional dash values to a StrokeStyle instance and adding a dash phase value, a range of different dash effects can be achieved, for example:. When drawing a shape, it is not possible to combine the fill and stroke modifiers to render a filled shape with a stroked outline. This effect can, however, be achieved by overlaying a stroked view on top of the filled shape, for example:. The shapes used so far in this chapter are essentially structure objects that conform to the Shape protocol.
A Path instance provides the outline of a 2D shape by specifying coordinates between points and defining the lines drawn between those points. In addition to being used in a custom shape implementation, paths may also be drawn directly within a view. Try modifying the ContentView. A path begins with the coordinates of the start point using the move method. Methods are then called to add additional lines between coordinates.
In this case, the addLine method is used to add straight lines. Lines may be drawn in a path using the following methods. In each case, the drawing starts at the current point in the path and ends at the specified end point:. The custom drawing may also be adapted by applying modifiers, for example with a green fill color:. Although it is possible to draw directly within a view, it generally makes more sense to implement custom shapes as reusable components.
Within the ContentView. The custom shape structure conforms to the Shape protocol by implementing the required path function. Now that the custom shape has been declared, it can be used in the same way as the built-in SwiftUI shapes, including the use of modifiers.
To see this in action, change the body of the main view to read as follows:. SwiftUI provides support for drawing gradients including linear, angular conic and radial gradients. In each case, the gradient is provided with a Gradient object initialized with an array of colors to be included in the gradient and values that control the way in which the gradient is rendered.
The following declaration, for example, generates a radial gradient consisting of five colors applied as the fill pattern for a Circle:. The following declaration, on the other hand, generates an angular gradient with the same color range:.
The final step in the DrawingDemo project is to apply gradients for the fill and background modifiers for our MyShape instance as follows:.
SwiftUI includes a built-in set of views that conform to the Shape protocol for drawing standard shapes such as rectangles, circles and ellipses.
Modifiers can be applied to these views to control stroke, fill and color properties. Custom shapes are created by specifying paths which consist of sets of points joined by straight or curved lines.
SwiftUI also includes support for drawing radial, linear and angular gradient patterns.A path is a list of lines, curves and other segments that all have absolute positions. While a path is absolute, a shape can choose to adjust its path to the given rect.
To draw a resizable vector asset in code, we can create a Shapeand then use the given rect to draw an absolute path. By default, the path is filled with the current foreground color.
Like a CGPathwe can also apply an affine transform to the path, giving us a new Path :. By using the Shape protocol, we can have much more control over paths. You can easily turn this into a more generic Fit struct that takes the path as a parameter.
For example, we can stroke a Path or a Shapewhich gives us back either a new Path or a new Shaperespectively. In conclusion: paths and shapes are almost the same. When you need an absolute drawing, you can use either one, but when you want to adjust the path to the available size, use a Shape. Swift Talk Episode explores SwiftUI paths and shapes in more depth, as we build an animated loading indicator for our Swift Talk app. The first episode is free to watch.
To watch the entire SwiftUI collection, subscribe here. We experiment with paths and shapes to create a triangular preview badge. Stay up-to-date with our newsletter or follow us on Twitter. In SwiftUI, there are two similar ways to draw shapes: A Path is a struct that contains the outline of a shape. Browse the Archive.SwiftUI enables custom drawing with two subtly different types: paths and shapes. In contrast, a shape has no idea where it will be used or how big it will be used, but instead will be asked to draw itself inside a given rectangle.
Helpfully, shapes are built using paths, so once you understand paths shapes are easy. Also, just like paths, colors, and gradients, shapes are views, which means we can use them alongside text views, images, and so on. SwiftUI implements Shape as a protocol with a single required method: given the following rectangle, what path do you want to draw? For example, previously we created a triangle using a Pathbut we could wrap that in a shape to make sure it automatically takes up all the space available like this:.
That job is made much easier by CGRectwhich provides helpful properties such as minX the smallest X value in the rectanglemaxX the largest X value in the rectangleand midX the mid-point between minX and maxX. Shapes also support the same StrokeStyle parameter for creating more advanced strokes:. The key to understanding the difference between Path and Shape is reusability: paths are designed to do one specific thing, whereas shapes have the flexibility of drawing space and can also accept parameters to let us customize them further.
To demonstrate this, we could create an Arc shape that accepts three parameters: start angle, end angle, and whether to draw the arc clockwise or not. If you look at the preview of our arc, chances are it looks nothing like you expect. We asked for an arc from 0 degrees to degrees with a clockwise rotation, but we appear to have been given an arc from 90 degrees to degrees with a counterclockwise rotation.
We can fix both of those problems with a new path in: method that subtracts 90 degrees from the start and end angles, and also flips the direction so SwiftUI behaves the way nature intended:. All data is attached automatically, and it only takes a line of code to setup. Start your free trial now and get 3 months off exclusively for the Hacking with Swift Community. Start your free trial! Sponsor Hacking with Swift and reach the world's largest Swift community! Start Here. About Hacking with Swift.
Im trying to detect when the user is scrolling and he arrives near to the bottom so I can load my next batch of data. The only time it gets trigger is when I pull up the screen after I'm at the bottom. So I need to go past the bottom in order for it to be triggered. I did this via finding out whether the object displayed is the last element in list, then by calling fetchMore function.
Add this fetchMoreEmployees employee: Employee function inside your ViewModel and call this function in. Learn more. Asked 2 days ago. Active today. Viewed 47 times. What am I doing wrong here? Rexhin Hoxha. Rexhin Hoxha Rexhin Hoxha 2, 4 4 gold badges 27 27 silver badges 70 70 bronze badges.
Active Oldest Votes. Zeona Zeona 12 12 bronze badges. I have used this for my chat pageso i need pagination logic when I scroll to top. Also, have sorted my array based on time.
RexhinHoxha Find out the index of your row object in array and compare it. Check whether it is the last element. RexhinHoxha please show the code used to build the list, so that I can help you. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. The Overflow Checkboxland.
Tales from documentation: Write for your clueless users.
Upcoming Events. Featured on Meta. Feedback post: New moderator reinstatement and appeal process revisions. The new moderator agreement is now live for moderators to accept across the…. Allow bountied questions to be closed by regular users.5 SwiftUI Concepts Every Beginning SwiftUI Developer Needs To Know (2020)
Hot Network Questions. Question feed.