HealthKit Swift getting today’s steps

HKStatisticsCollectionQuery is better suited to use when you want to retrieve data over a time span. Use HKStatisticsQuery to just get the steps for a specific date.

Swift 5:

let healthStore = HKHealthStore()

func getTodaysSteps(completion: @escaping (Double) -> Void) {
    let stepsQuantityType = HKQuantityType.quantityType(forIdentifier: .stepCount)!
    
    let now = Date()
    let startOfDay = Calendar.current.startOfDay(for: now)
    let predicate = HKQuery.predicateForSamples(
        withStart: startOfDay,
        end: now,
        options: .strictStartDate
    )
    
    let query = HKStatisticsQuery(
        quantityType: stepsQuantityType,
        quantitySamplePredicate: predicate, 
        options: .cumulativeSum
    ) { _, result, _ in
        guard let result = result, let sum = result.sumQuantity() else {
            completion(0.0)
            return
        }
        completion(sum.doubleValue(for: HKUnit.count()))
    }
    
    healthStore.execute(query)
}