Font size issues between iOS and macOS

[brendand]

How do you get the text in a RichTextEditor look approximately the same size as text with the same content on macOS?

I've been looking into the UITextView's usesStandardTextScaling property to try and figure this out. Apple states:

When the value of this property is true, UIKit automatically adjusts the rendering of the text in the text view to match the standard text scaling.
When using the standard text scaling, font sizes in the text view appear visually similar to how they would render in macOS and non-Apple platforms, and copying the contents of the text view to the pasteboard preserves the original font point sizes. This effectively changes the display size of the text without changing the actual font point size. For example, text using a 13-point font in iOS looks like text using a 13-point font in macOS.
If your app is built with Mac Catalyst, or if your text view’s contents save to a document that a user can view in macOS or other platforms, set this property to true.
The default value of this property is false.

but when I enable that on the RichTextView, it messes up the insertion pointer and doesn't display the text across the entire width of the UITextView like it should. Plus worse of all, the insertion pointer and selection blocks go all wonky.

I don't have a Mac Catalyst app. It's AppKit. I also have an iOS version. They display the same NSAttributedString data, but on iOS, the text renders too small. But if you change the text size on iOS to be more readable, then on macOS it's too large.

Basically how do you use RichTextKit to display the same size text on both macOS and iOS?

Here's two screenshots. Both showing the same paragraph selected.

The first one where the selection looks proper and matches the text is with usesStandardTextScaling = false. But the text is small and should render larger (without changing the point size of the text) so it visually matches what's seen on the Mac.

The second one is with usesStandardTextScaling = true and you can see the text isn't rendering larger as it should AND the selection area is offset from the content. It seems like the text needs to be shifted to the right and zoomed in a bit to make it fit the blue selection area.

How do other people handle text size issues between macOS and iOS apps?

[danielsaidi]

Hi @brendand

Keeping a standard font size has been problematic, and it should be improved.

I'm struggling with finding time for this project at the moment, but will hopefully have time later in H1. Until then, I'm happy to take a look at anything the community comes up with.

[brendand]

So it's not just me holding it wrong? I'm pretty sure that Apple handles this sort of thing properly in apps like Notes and Pages between platforms. Would be great to know what tricks they use. I thought the usesStandardTextScaling = true was going to be the holy grail to solve this issue.

[danielsaidi]

I'm not sure. I agree that usesStandardTextScaling sounds like the thing to use. Could it be something in how SwiftUI wraps the native view that causes this?

[brendand]

It happens with a regular UITextView. Not just RichTextKit. I filed a feedback on it in 2022 with a sample app, but never heard back from Apple on that. It was feedback FB11274733. You can try it out yourself. Attaching sample app.

TextViewCursorBug.zip

[brendand]

I seem to have resolved this problem by instead of using NSKeyedArchiver and unarchiver to encode and decode my NSAttributedString, I encode the string to RTFD and back. Then when I provide the decoded NSAttributedString to RichTextKit, the visual size is equivalent between platforms. The usesStandardTextScaling property does not come into play with this technique. In fact, enabling it still screws up editing and display. So just encoding and decoding to RTFD solves the problem for me. When you encode to RTFD, I get back a Data object which I then store in my database and then retrieve it later and decode it from RTFD and all is good.

[danielsaidi]

Oh, that sounds great! How do you do the RTFD encoding and decoding?

[brendand]

Decode from Data to NSAttributedString:

extension Data {
    public func attributedStringFromRTFD() throws -> NSAttributedString? {
        do {
            let string = try NSAttributedString(data: self, options: [.documentType: NSAttributedString.DocumentType.rtfd], documentAttributes: nil)
            return string
        } catch {
            print(error)
        }
        return nil
    }
}

Encode from NSAttributedString to RTFD Data:

extension NSAttributedString {
 @objc public func rtfd() throws -> Data {
        try data(.rtfd)
    }
    func data(_ documentType: NSAttributedString.DocumentType) throws -> Data {
        return try data(from: .init(location: 0, length: length),
                        documentAttributes: [.documentType: documentType])
    }
}

So then just call attributedString.rtfd() to get a Data object you can store. And then let attributedString = rtfdDataBlob.attributedStringFromRTFD() to get your string.

When you get the NSAttributedString from the data, it seems to have the necessary source information in it that tells macOS and iOS how to render the text at a visually comparable size between platforms.

Seems to work for me.

[danielsaidi]

Thank you so much @brendand - I would love to replace archiving with RTFD if it's possible.