【SwiftUI】解决使用SwiftData时Preview报错

@Model
public class SampleData{
    public var content:String?
}

let container: ModelContainer = {
    try! ModelContainer(
        for: SampleData.self
    )
}()

struct ContentView: View {

    @Query var datas: [SampleData]?
    ///......其他内容
}

#Preview {
    ContentView()
}

以上代码在Preview时会抛出异常：failed to find a currently active container for SampleData，但是真机运行没有异常。

解决方案：

修改PreView如下：

#Preview {
    MainActor.assumeIsolated {
        let container = container
        return ContentView()
               .modelContainer(container)
    }
}

或

 @MainActor
 let previewContainer: ModelContainer = {
    do {
        let container = try ModelContainer(
                for: SampleData,
                configurations: ModelConfiguration(isStoredInMemoryOnly: true)
            )
        let modelContext = container.mainContext
        if try modelContext.fetch(FetchDescriptor< SampleData >()).isEmpty {
            container.mainContext.insert(SampleData(content:"test"))
        }
        return container
    } catch {
        fatalError("Failed to create container")
    }
}()

#Preview {
    ContentView()
    .modelContainer(previewContainer)
}

参考：

https://developer.apple.com/forums/thread/731511