如何在 SwiftUI 中使用 NSAttributedString 和 ScrollView?

How to use an NSAttributedString with a ScrollView in SwiftUI?(如何在 SwiftUI 中使用 NSAttributedString 和 ScrollView?)

问题描述

我已经能够通过 UIViewRepresentable 呈现 NSAttributedString，这在我将视图包装在 ScrollView 之前效果很好.

I've been able to render NSAttributedStrings via UIViewRepresentable which works great until I wrap the view in a ScrollView.

当放置在 ScrollView 内时，NSAttributedString 视图会停止渲染.

When placed inside the ScrollView, the NSAttributedString view stops rendering.

我尝试了一些其他方法来替换 NSAttributedString 并添加多个 Text() 视图以获得在 ScrollView 并支持斜体和等宽字体.不幸的是，这对于文本块内的 links 不起作用，这意味着我仍然需要一个 NSAttributedString.

I've tried some other methods that replace an NSAttributedString with adding multiple Text() views together to get formatting which works inside the ScrollView and supports italics and monospace font. Unfortunately this doesn't work for links inside text blocks, which means I still need an NSAttributedString.

import SwiftUI

struct TextWithAttributedString: UIViewRepresentable {

    var attributedString: NSAttributedString

    init(_ attributedString: NSAttributedString) {
        self.attributedString = attributedString
    }

    func makeUIView(context: Context) -> UITextView {
        let textView = UITextView(frame: .zero)
        textView.attributedText = self.attributedString
        textView.isEditable = false
        return textView
    }

    func updateUIView(_ textView: UITextView, context: Context) {
        textView.attributedText = self.attributedString
    }
}


let exampleText = """
Fugiat id blanditiis et est culpa voluptas. Vivamus aliquet enim eu blandit blandit. Sit eget praesentium maxime sit molestiae et alias aut.
"""

struct NSAttributedStringView: View {
    var body: some View {
// Note: when uncommented, the view breaks
//    ScrollView {
        TextWithAttributedString(NSAttributedString(string: exampleText))
//    }
    }
}

struct NSAttributedStringView_Previews: PreviewProvider {
    static var previews: some View {
        NSAttributedStringView()
            .previewLayout(.sizeThatFits)
    }
}

我尝试使用包装的 UITextView 并设置 text 属性而不是 attributeText 属性，但这也无法在 ScrollView 中呈现，所以问题似乎是 UITextView，而不是 NSAttributedString.

I tried using the wrapped UITextView with the text property set instead of the attributeText property, but this also fails to render in the ScrollView, so the issue seems to be the UITextView, not the NSAttributedString.

所以问题是，我们如何让 UITextView 在 ScrollView 中工作?

So the question is, how do we get the UITextView to work in a ScrollView?

推荐答案

原因是SwiftUI ScrollView 需要定义内容大小，但是使用的UITextView 本身就是一个UIScrollView 并根据父视图中的可用空间检测内容.因此，它发生了未定义大小的循环.

The reason is that SwiftUI ScrollView requires defined content size, but used UITextView is itself a UIScrollView and detects content based on available space in parent view. Thus it happens cycle of undefined sizes.

以下是解决此问题的可能方法的简化演示.这个想法是计算 UITextView 的内容大小并将其传递给 SwiftUI...

Here is a simplified demo of possible approach how to solve this. The idea is to calculate content size of UITextView and pass it to SwiftUI...

struct TextWithAttributedString: UIViewRepresentable {
    @Binding var height: CGFloat
    var attributedString: NSAttributedString

    func makeUIView(context: Context) -> UITextView {
        let textView = UITextView(frame: .zero)
        textView.isEditable = false
        return textView
    }

    func updateUIView(_ textView: UITextView, context: Context) {
        textView.attributedText = self.attributedString

        // calculate height based on main screen, but this might be 
        // improved for more generic cases
        DispatchQueue.main.async { // << fixed 
            height = textView.sizeThatFits(UIScreen.main.bounds.size).height
        }
    }
}


struct NSAttributedStringView: View {
    @State private var textHeight: CGFloat = .zero
    var body: some View {
        ScrollView {
            TextWithAttributedString(height: $textHeight, attributedString: NSAttributedString(string: exampleText))
                .frame(height: textHeight) // << specify height explicitly !
        }
    }
}

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