无法从自定义框架呈现SwiftUI预览

Question

我正在尝试在自定义框架中编写SwiftUI视图。

之所以这样做是因为我想隐藏子视图的实现，因为Swift没有提供命名空间。因此，我做了一个子框架，并在其中实现了测试视图。

所以我想做

1. 制作一个应用（名称：singleview）
2. 制作一个子模块（名称：Framework，名为Calendar）
3. 导出视图（名称：单元格）
4. 两者都预览（*）

然后我得到了

1. 构建并成功运行
2. 我可以看到应用程序ContentView的预览

但是问题是：

• 我无法看到Cell的预览（在框架Calendar内部），并显示以下错误：

'Cell_Previews' is not a member type of 'Calendar'

----------------------------------------

BuildError: Failed to build Cell.swift

Compiling failed: 'Cell_Previews' is not a member type of 'Calendar'

failedToBuildDylib: /Users/q/Library/Developer/Xcode/DerivedData/singleview-cmqdlfabgiintkgnvdpzzagojvzf/Build/Intermediates.noindex/Previews/singleview/Intermediates.noindex/Calendar.build/Debug-iphonesimulator/Calendar.build/Objects-normal/x86_64/Cell.2.preview-thunk.swift:22:36: error: 'Cell_Previews' is not a member type of 'Calendar'
typealias Cell_Previews = Calendar.Cell_Previews
                          ~~~~~~~~ ^
/Users/q/Library/Developer/Xcode/DerivedData/singleview-cmqdlfabgiintkgnvdpzzagojvzf/Build/Intermediates.noindex/Previews/singleview/Intermediates.noindex/Calendar.build/Debug-iphonesimulator/Calendar.build/Objects-normal/x86_64/Cell.2.preview-thunk.swift:6:6: error: replaced accessor for 'previews' could not be found
    @_dynamicReplacement(for: previews) private static var __preview__previews: some View {
     ^
/Users/q/Library/Developer/Xcode/DerivedData/singleview-cmqdlfabgiintkgnvdpzzagojvzf/Build/Intermediates.noindex/Previews/singleview/Intermediates.noindex/Calendar.build/Debug-iphonesimulator/Calendar.build/Objects-normal/x86_64/Cell.2.preview-thunk.swift:21:27: error: 'Cell' is not a member type of 'Calendar'
typealias Cell = Calendar.Cell
                 ~~~~~~~~ ^
/Users/q/Library/Developer/Xcode/DerivedData/singleview-cmqdlfabgiintkgnvdpzzagojvzf/Build/Intermediates.noindex/Previews/singleview/Intermediates.noindex/Calendar.build/Debug-iphonesimulator/Calendar.build/Objects-normal/x86_64/Cell.2.preview-thunk.swift:14:6: error: replaced accessor for 'body' could not be found
    @_dynamicReplacement(for: body) private var __preview__body: some View {
     ^

那么，如果我想查看预览，该怎么办？

这是该项目的屏幕截图

这是失败的屏幕截图

我正在使用Xcode 11.2.1（11B500）。

谢谢！

---

编辑：谢谢克里斯！ Cell.swift（在框架内部）的代码是：

import SwiftUI

public struct Cell: View {
    public init() {}

    public var body: some View {
        Text("INTERNAL")
    }
}

public struct Cell_Previews: PreviewProvider {
    public init() {}

    public static var previews: some View {
        Cell()
    }
}

ContentView.swift（框架的用户）为：

import SwiftUI
import Calendar

struct ContentView: View {
    var body: some View {
        Cell()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}