可以使用 WatchKit 与 HealthKit 框架来获取 Apple Watch 的 PPG 数据。

首先，在 Watch App 中，需要在 Interface.storyboard 上添加一个WKInterfaceController，然后使用 WKInterfacePicker 控件设置时间间隔，并使用 WKInterfaceLabel 在 Watch App 中显示步骤进度。接着，通过 HealthKit 框架获取实时的 PPG 数据，并将其传输到 Watch App 上。代码示例：

// 导入 WatchKit 和 HealthKit 框架 import WatchKit import HealthKit

class InterfaceController: WKInterfaceController {

@IBOutlet weak var timePicker: WKInterfacePicker!
@IBOutlet weak var stepLabel: WKInterfaceLabel!

// 实例化 HealthStore 对象
let healthKitStore = HKHealthStore()

override func awake(withContext context: Any?) {
    super.awake(withContext: context)
    
    // 配置时间间隔的选项
    var pickerItems: [WKPickerItem] = []
    
    for i in stride(from: 1, to: 61, by: 1) {
        let pickerItem = WKPickerItem()
        pickerItem.title = "\(i) 秒"
        pickerItems.append(pickerItem)
    }
    
    timePicker.setItems(pickerItems)
    timePicker.setSelectedItemIndex(9)
}

@IBAction func startBtnTapped() {
    // 获取时间间隔
    let pickerIndex = timePicker.selectedIndex
    let intervalStr = timePicker.item(at: pickerIndex)?.title
    let interval = Double(intervalStr!.split(separator: " ")[0])
    
    // 配置实时 PPG 查询器
    let sampleType = HKObjectType.quantityType(forIdentifier: .heartRate)!
    let query = HKObserverQuery(sampleType: sampleType, predicate: nil) { (query, completionHandler, error) in
        let calendar = Calendar.current
        let endDate = Date()
        let startDate = calendar.date(byAdding: .second, value: -Int(interval!), to: endDate)!
        let predicate = HKQuery.predicateForSamples(withStart: startDate, end: endDate, options: .strictEndDate)
        let sortDescriptor = NSSortDescriptor(key: HKSampleSortIdentifierStartDate, ascending: false)
        let query = HKSampleQuery(sampleType: sampleType, predicate: predicate, limit: Int(HKObjectQueryNoLimit), sortDescriptors: [sortDescriptor]) { (query, samples, error) in
            
            if let samples = samples as? [HKQuantitySample] {
                // 获取最新的 PPG 数据
                if let latestQuantity = samples.first?.quantity {