Swift:表达式类型在没有更多上下文的情况下不明确

Question

let healthWrite = Set(arrayLiteral:[
    HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierBodyMassIndex),
    HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierActiveEnergyBurned),
    HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierDistanceWalkingRunning),
    HKQuantityType.workoutType()
])

Answer 1

构造函数需要一个数组文字而不是数组，所以你可以用这样的东西来初始化

let healthWrite = Set(arrayLiteral:
     HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierBodyMassIndex)!,
     HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierActiveEnergyBurned)!,
     HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierDistanceWalkingRunning)!,
     HKQuantityType.workoutType()
     )

有关数组和数组文字的更多信息 https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/CollectionTypes.html

编辑:

让你悲伤的是可选值而不是“[]”

let healthWrite = Set([
            HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierBodyMassIndex)!,
            HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierActiveEnergyBurned)!,
            HKObjectType.quantityTypeForIdentifier(HKQuantityTypeIdentifierDistanceWalkingRunning)!,
            HKQuantityType.workoutType()]
            )

如果您在创建集合之前使用 guard 或 if let 来检查 HKObjectType.quantityTypeForIdentifier 是否实际返回一个值，效果会更好