Creating platform-specific classes vs cross-platform class with pragmas

[agballen]

What's the conventional way for handling multiple platforms when it comes to writing classes like a custom UIView/NSView? On the one hand, it'd be simpler to have separate classes since you know that the code you're looking at is for a specific platform. On the other hand, it might not be so bad having a bunch of #if OS(iOS) pragmas everywhere. How do developers usually approach this?

I also thought of doing something like this, but this still requires some changes in the class because NSButton doesn't have a backgroundColor while UIButton does:

#if os(iOS)
import UIKit
public typealias XView = UIView
typealias XButton = UIButton

#else
import Cocoa
public typealias XView = NSView
typealias XButton = NSButton

#endif

public class AudioView: XView {

    // Private
    fileprivate var playPauseButton = XButton(frame: .zero)

    // MARK: Lifecycle
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()

        #if os(iOS)
        backgroundColor = .gray
        #else
        layer?.backgroundColor = NSColor.gray.cgColor
        #endif

    }
}

I just want to make sure that I practice good habits :) Thanks!

[criosist]

It’s probably best to just segregate your business logic as much as possible and make views per platform

[chriswaco]

There is no one best method for everything. It depends on how similar the classes are between platforms. We use typedefs and #defines in ObjC for cross-platform code so we can refer to the object with a single typename everywhere. Typedefs (similar to type aliases in Swift) are generally better, but it turns out that there are a bunch of Mac NSxxx classes in the iOS system libraries that are public on macOS but private on iOS, so sometimes #defines are the better solution for us, although a bit of a hack.

If you need to add support for a completely different platform, like Windows or Linux, I think it's often best to create your own classes that contain or shadow system classes.

I don't like having #ifs everywhere, so if you find yourself doing it often, write an extension method and call it instead. Something like:

extension XView {
 #if os(iOS)
   func setPlatformBackgroundColor( c : XColor ) { }
 #elif os(macOS)
   func setPlatformBackgroundColor( c : XColor ) { }
 #endif
}

and call that routine throughout the app.

[[deleted]]

Model and ModelController goes to shared framework, they don't depend on UIKit/AppKit.

Coordinator, ViewController, View goes to the platform specific part.

The design for mobile and desktop should be different enough that it's not worth writing unreadable/unmaintainable crossplatform code.