我们如何将 Objective-C 常量导入为 Swift 类型？

Question

I want to declare constant in Swift 3 . For example if we have following constant in Objective-C :

HK_EXTERN NSString * const HKQuantityTypeIdentifierHeight;
HK_EXTERN NSString * const HKQuantityTypeIdentifierBodyMass;

Answer 1

Add New Swift file : Constant.swift

import Foundation
import HealthKit

let HK_EXTERN_Height : NSString = HKQuantityTypeIdentifierHeight
let HK_EXTERN_BodyMass : NSString = HKQuantityTypeIdentifierBodyMass

Use in ViewController.swift

print(HK_EXTERN_Height)
print(HK_EXTERN_BodyMass)

Hope this help you....

Answer 2

Adding constants into a separate file is also possible in Swift.

For using constants, it is even smarter, if you use structs , because huge number of constants can be messy:

import HealthKit

struct Constants {

    struct Health {

        struct Quantities {
            let height : NSString = HKQuantityTypeIdentifierHeight
            let bodyMass : NSString = HKQuantityTypeIdentifierBodyMass
            static let minWeight: Double = 30.0
        }  
        ...          
    } 
    ...
}

Usage:

print(Constants.Health.Quantities.minWeight)

or

let healthNumbers = Constants.Health.Quantities
print(healthNumbers.minWeight)

Answer 3

我相信在 Swift 语言中，您可以使用 let 关键字进行声明。