Provide better support for SwiftUI and AttributedString.

[makhocheung]

Here is the example.

import Combine
import SwiftUI
import ZMarkupParser

struct MainView: View {
    @State var content = AttributedString("None")
    var body: some View {
        ScrollView {
            VStack {
                Text(content)
            }
        }
        .onAppear {
            content = AttributedString(parser.render(html))
        }
    }
}

struct MainView_Previews: PreviewProvider {
    static var previews: some View {
        MainView()
    }
}

let parser = ZHTMLParserBuilder.initWithDefault().set(rootStyle: MarkupStyle(font: MarkupStyleFont(size: 13))).build()

let html = #"""

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<h1>不支持</h1>
<h2>不支持</h2>
<h3>不支持</h3>
<h4>不支持</h4>
<h5>不支持</h5>
<h6>不支持</h6>

"""#

Here is the error printed by console.

2023-03-13 16:46:54.445491+0800 Demo[41916:3803493] [Demo] CGImageDestinationCreateWithData:4044: *** ERROR: CGImageDestinationCreateWithData: invalid capacity (0)
2023-03-13 16:46:54.445856+0800 Demo[41916:3803493] [Demo] finalizeDestination:3205: *** ERROR: CGImageDestinationFinalize was called, but there were no images added
2023-03-13 16:46:54.445881+0800 Demo[41916:3803493] CGImageDestinationFinalize failed for output type 'public.tiff'

[zhgchgli0718]

Hi, @makhocheung thank you for using and providing feedback.

From the content of your issue, I have identified three problems that need to be resolved:

• Easy - Support h1~h6. This is not a bug, but an extension is needed to support H tags.
• Easy - I saw a log message that says "failed for output type 'public.tiff'" on macOS, which means I have a misunderstanding of AppKit's NSImage. This issue is also related to ZNSTextAttachment.
• Need research - Make AttributedString support ZNSTextAttachment. Currently, we use ZNSTextAttachment to represent images.

I'll resolve it as soon as possible.

Thank you again for your feedback, I have not fully tested on macOS or using SwiftUI yet.

[zhgchgli0718]

After conducting research, I have concluded that AttributedString and NSAttributedString are not small objects and do not share the same inheritance.
Therefore, I believe that using NSAttributedString in AttributedString or SwiftUI is not a good idea.
Instead, we should create a new mapper to map ZMarkupParser.Markup objects to SwiftUI Kit (Text/Image) components, rather than using NSAttributedString directly in AttributedString.

Unfortunately, it may not be implemented quickly.

A temporary dirty solution would be to find ZNSTextAttachment for each AttributedString and manually trigger startDownload() and handle delegate for it.

content.compactMap({ $0.attachment as? ZNSTextAttachment }).forEach { attachment in
     attachment.delegate = self
    attachment.startDownlaod()
})
// handler delegate
func zNSTextAttachment(didLoad textAttachment: ZNSTextAttachment, to: ZResizableNSTextAttachment) {
     //
    replace  textAttachment to to in AttributedString
}

I know it's very dirty, but as I mentioned earlier, it's not recommended to use it in SwiftUI currently.

[zhgchgli0718]

Please let me know if there is anything I have misunderstood, as I am not very familiar with SwiftUI.

[makhocheung]

Currently，AttributedString supports markdown natively except ![]()，so it's normal that AttributedString can't load remote images. Maybe Apple will add this feature in the future.

we should create a new mapper to map ZMarkupParser.Markup objects to SwiftUI Kit (Text/Image) components, rather than using NSAttributedString directly in AttributedString.

This is a good idea. Developers may hope ZMarkupParser supports SwiftUI.

Actually, I'm appreciate that you have added support of h1~h6. ZMarkupParser currently satisfies my project. I will give more feedback later. Thank you.

[charrondev]

I'll add on here that this is really more of a failing of a failing of SwiftUI's Text() than of this library. It is very simple to convert between the 2 nowadays.

let nsAttr = parser.render(html)
let attr = AttributedString(nsAttr)

The real issue is that AttributedString and Text() are missing a lot of functionality, most notably support for NSParagraphStyle which you need to do paragraph level alignment, spacing, lineSpacing, justification, etc.

For my own projects I use a UIViewRepresentable wrapping a UITextView to get the maximum flexibility.