Widget参数默认值失效：BackgroundQuery defaultResult不生效排查

我开发的Widget支持location和background两个自定义参数，location选择器能正常遵循LocationQuery的defaultResult设置默认值，但background选择器却忽略BackgroundQuery的defaultResult，Xcode抛出如下警告：

Error getting AppIntent from LNAction: AppIntent has missing parameter value for 'background'. You may need to set a default value in the initializer of your @Parameter, or using the default method on your Query.
No AppIntent in timeline(for:with:)

请问为何两者表现不一致？

相关代码 #

struct BackgroundQuery: EntityQuery {
    func entities(for identifiers: [String]) ->  [WidgetBackground]  {
        [
            WidgetBackground(id: "Background1"),
            WidgetBackground(id: "Background2")
        ].filter { identifiers.contains($0.id) }
    }
    
    func suggestedEntities() -> [WidgetBackground] {
        [
            WidgetBackground(id: "Background1"),
            WidgetBackground(id: "Background2")
        ]
    }
    
    func defaultResult() -> WidgetBackground {
        return WidgetBackground(id: "Background1")
    }
}

struct WidgetBackground: AppEntity {
    var id: String
    
    static var typeDisplayRepresentation: TypeDisplayRepresentation = "Background"
    static var defaultQuery = BackgroundQuery()
    
    var displayRepresentation: DisplayRepresentation {
        DisplayRepresentation(title: "\(NSLocalizedString(id, comment: "").description)")
    }
    
    init(id: String) {
        self.id = id
    }
}


struct LocationQuery: EntityQuery {
    func entities(for identifiers: [LocationDetail.ID]) async throws -> [LocationDetail] {
        LocationDetail.getAllLocations().filter { identifiers.contains($0.id) }
    }
    
    func suggestedEntities() async throws -> [LocationDetail] {
        LocationDetail.getAllLocations()
    }
    
    func defaultResult() async -> LocationDetail? {
        try? await suggestedEntities().first
    }
}


struct SelectLocationIntent: WidgetConfigurationIntent {
    static var title: LocalizedStringResource = "Avalanche Reports Location"
    static var description = IntentDescription("Select the location of the displayed avalanche reports.")

    @Parameter(title: "Location")
    var locationDetail: LocationDetail
    
    @Parameter(title: "Background")
    var background: WidgetBackground
}

问题原因与解决方案 #

核心问题是两个EntityQuery的defaultResult方法签名不匹配：

• LocationQuery使用了Widget配置Intent要求的现代异步可选签名：async -> LocationDetail?
• BackgroundQuery仍用旧的同步非可选签名：-> WidgetBackground

系统无法识别同步版本的defaultResult，因此认为background参数缺少默认值，抛出警告。

修改BackgroundQuery的方法签名，对齐异步可选模式，同时将其他查询方法也改为异步：

struct BackgroundQuery: EntityQuery {
    func entities(for identifiers: [String]) async -> [WidgetBackground] {
        [
            WidgetBackground(id: "Background1"),
            WidgetBackground(id: "Background2")
        ].filter { identifiers.contains($0.id) }
    }
    
    func suggestedEntities() async -> [WidgetBackground] {
        [
            WidgetBackground(id: "Background1"),
            WidgetBackground(id: "Background2")
        ]
    }
    
    func defaultResult() async -> WidgetBackground? {
        WidgetBackground(id: "Background1")
    }
}

这样修改后，background参数的默认值就能被系统正确加载，和location参数的表现一致。

内容的提问来源于stack exchange，提问作者Fez Vrasta