SwiftUI views are values and not objects!
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Last Updated on May 20, 2023 by Deya Eldeen

In SwiftUI, views are value types rather than traditional objects 🧐, this design approach is a fundamental aspect of SwiftUI’s declarative programming model and is aligned with the Swift language’s emphasis on value semantics.

As value types, views in SwiftUI are immutable and are copied when needed, resulting in predictable behavior and easy management of state and data flow, this means that when you modify a view, you are actually creating a new instance with the desired changes, rather than mutating the existing view, this immutability allows SwiftUI to efficiently track changes and perform targeted updates to the user interface.

Value types promote a more functional and declarative style of programming, where you describe the desired state and SwiftUI takes care of updating the view hierarchy accordingly, they are also thread-safe by default, as copies are made when passing views between different execution contexts.

Another advantage of using value types for views is that they enable SwiftUI’s built-in animations and transitions, by comparing the old and new values of a view, SwiftUI can automatically animate the changes, resulting in smooth and visually appealing user interface updates.

The declarative programming paradigm is at the core of its design philosophy, declarative programming focuses on describing the desired state of the user interface rather than specifying step-by-step instructions on how to achieve that state, SwiftUI’s view tree engine leverages this approach to efficiently manage and update the user interface based on changes in the underlying state.

You define your user interface using a hierarchy of composable and reusable views. Each view represents a specific part of the interface and is responsible for rendering itself based on the current state, by composing these views together, you create a tree-like structure known as the view hierarchy, the view hierarchy in SwiftUI is immutable, meaning that you define it once and SwiftUI takes care of updating it based on changes to the underlying state, when the state changes, (or even when the view re-appears when scrolling back and forth), SwiftUI re-evaluates the view hierarchy and determines the minimal set of updates needed to reflect the new state, this process is known as the reconciliation algorithm (AKA diffing algorithm).

The reconciliation algorithm is where SwiftUI’s view tree engine shines. It efficiently compares the old and new view hierarchies, identifies the differences, and applies the necessary updates to the user interface, by only updating the specific parts of the view hierarchy that have changed, SwiftUI minimizes the amount of work needed to keep the UI in sync with the state, resulting in optimal performance.

In contrast to UIKit, in SwiftUI view construction and updates are unified into a single code path, views are values rather than objects, described by values conforming to the View protocol, the view tree is transient and can be recreated at any time based on the underlying state, this declarative approach eliminates the need for separate event handlers and manual UI updates like in UIKit, SwiftUI’s view tree engine efficiently reconciles state changes, performs targeted updates, and ensures a reactive UI that stays in sync with the data, by relying on value semantics, SwiftUI can perform granular updates and avoid unnecessary computations, leading to a highly performant and responsive user interface.

By relying on a declarative approach, SwiftUI allows developers to focus on describing the desired end state of the UI rather than worrying about the low-level details of UI manipulation, this shift in mindset 😎 leads to more maintainable and expressive code, as developers can easily reason about the UI based on its desired state.

Another significant aspect of SwiftUI’s view tree engine is its ability to efficiently handle updates. As views in SwiftUI are value types, changes in the state result in the creation of new view instances rather than mutating existing ones. SwiftUI employs a mechanism called “value comparison” to determine the differences between the old and new views, enabling it to perform targeted updates to the UI.

Additionally, SwiftUI’s view tree engine embraces a reactive programming model. Views in SwiftUI are not just passive representations of UI elements but are also capable of reacting to changes in the state, this reactive nature enables automatic propagation of state changes throughout the view hierarchy, ensuring that the UI remains synchronized with the underlying data.

In conclusion, SwiftUI’s view tree engine revolutionizes UI development by embracing the declarative programming paradigm. It provides an efficient and responsive user interface by leveraging value types, value comparisons, and reactive programming.

The ability to describe UI in a declarative manner, combined with targeted updates and optimization techniques, empowers developers to create intuitive and performant user interfaces with ease.


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