Скачать или смотреть How to Use the NSView Initializer in Swift: Tips and Tricks for Custom Subclasses

Learn how to effectively manage the initializers in your Swift `NSView` subclasses, ensuring you can use `init()` while adhering to Cocoa's design.
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This video is based on the question https://stackoverflow.com/q/75397505/ asked by the user 'ios coder' ( https://stackoverflow.com/u/13899957/ ) and on the answer https://stackoverflow.com/a/75398936/ provided by the user 'vadian' ( https://stackoverflow.com/u/5044042/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering the NSView Initializer in Swift

Creating custom views in macOS applications using Swift can sometimes lead to confusion, especially when it comes to initializers. A common question developers face is how to remove or disable certain initializers inherited from the NSView superclass. Specifically, many want to streamline their subclass to use just init(). Let's dive into this problem and demystify how to work with initializers in Swift.

Problem Overview

When subclassing NSView, you may encounter several initializers that do not fit your desired implementation. For example, if you want your subclass, say MyNSView, to be initialized simply with init(), it can be frustrating to find that NSView includes designated initializers like init(frame:) and init(coder:) that cannot be easily removed.

The Code Dilemma

A developer posed the following code snippet and sought a solution:

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The intention was clear: to have a subclass that could be initialized only via init(). Unfortunately, this approach doesn’t work as intended.

The Solution

Understanding Initializers

In Swift, initializers are critical to setting up your objects. Here’s how they break down for NSView:

Designated Initializers: These are the primary initializers for a class. For NSView, init(frame:) is the designated initializer.

Convenience Initializers: These are secondary, or additional, initializers that call the designated initializer. They provide a simpler interface to instantiate the class.

Given this framework, you cannot entirely "remove" the designated initializers; however, you can manage how they're called.

Implementing a Convenience Initializer

To still be able to use init(), you can implement a convenience initializer that internally calls the designated initializer. Here’s how you should structure your MyNSView subclass:

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Why This Works

By calling self.init(frame: .zero), you're respecting the class's initialization requirements while conveniently providing a simpler way to create your view. The .zero frame initializes your view with no specific dimensions, which is often acceptable during the initial setup.

Working with Interface Builder

If your view is designed within Interface Builder, be aware that the init(coder:) initializer will be called. This means that if your view is being loaded from a storyboard or XIB file, you still need to provide an implementation of this initializer. Here’s a possible implementation:

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Final Thoughts

While you cannot completely detach from the required initializers of the NSView superclass, you can effectively manage how your subclass initializes. Using convenience initializers and understanding the role of designated initializers can greatly help streamline your code.

By following this structure, you ensure that your subclass is both functional and adheres to the Cocoa framework's standards. Happy coding!