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Dovizu's questions

Martin Hope
Dovizu
Asked: 2024-11-25 07:22:04 +0800 CST
  • 5

我试图了解为什么 SwiftUI Preview 不允许我这样做：

struct ItemCreateView: View {
    
    @Environment(\.dismiss) var dismiss
    @Environment(\.modelContext) private var modelContext
    
    @Query private var collections: [Collection]
    let selectedCollection: Collection
    
    @State private var item = Item()
    @State private var selectedImage: PhotosPickerItem? = nil
    
    var body: some View {...}
}

#Preview {
    let config = ModelConfiguration(isStoredInMemoryOnly: true)
    let container = try! ModelContainer(for: Collection.self, configurations: config)
    
    for number in 1...10 {
        let col = Collection(name: "Test Collection \(number)")
        container.mainContext.insert(col)
    }
    
    let selectedCollection = container.mainContext.fetch(Collection.self).first!
    
    ItemCreateView(selectedCollection: selectedCollection).modelContainer(container)
}

错误是：

No exact matches in call to macro 'Preview'
Closure containing control flow statement cannot be used with
result builder 'PreviewMacroBodyBuilder'

但是，如果我将“Return”添加到最后一项。它会抱怨：Cannot use explicit 'return' statement in the body of result builder 'ViewBuilder'

但如果我不尝试从容器中获取随机元素，一切都会正常。

#Preview {
    let config = ModelConfiguration(isStoredInMemoryOnly: true)
    let container = try! ModelContainer(for: Collection.self, configurations: config)
    
    for number in 1...10 {
        let col = Collection(name: "Test Collection \(number)")
        container.mainContext.insert(col)
    }
    
    let selectedCollection = Collection(name: "Test Collection 1")
    
    return ItemCreateView(selectedCollection: selectedCollection).modelContainer(container)
}

^ 这有效。

我不确定我是否理解这里所有内容的关联，而且我似乎无法在网上找到有关该错误的信息。

提前感谢您的帮助。

参考模型

@Model
final class Collection {
    var name: String
    @Relationship(inverse: \Item.collection) var items: [Item]
    var timestamp: Date
    
    init(name: String = "", items: [Item] = [], timestamp: Date = Date()) {
        self.name = name
        self.items = items
        self.timestamp = timestamp
    }
}
xcode