arrays - 如何在 SwiftUI 中计算数组的总计、小计和平均值
问题描述
我是 SwiftUI 的新手,我已经坚持了几天。
我有一个可识别的无序数组。我在父视图中有一个用于该数组的过滤器,并且过滤器的值传递给子视图。
我需要根据数组中一个元素的值对元素进行分组,然后根据每个数组元素中设置的另一个值计算总计、小计和平均值。
计算需要根据父视图中设置为 true 或 false 的过滤器进行更新。
我通过在 ForEach 视图中进行计算在 JavaScript (React) 中轻松解决了这个问题,但不知道如何在 SwitUI 中解决这个问题。
非常感谢任何帮助!
struct Student: Identifiable {
let id: String
let name: String
let gradeLevel: Int
let studyHours: Int
}
class GetStudents: ObservableObject {
@Published var items = [Student]()
init() {
self.items = [
Student(id: "aa1", name: "Bobby", gradeLevel: 9, studyHours: 2),
Student(id: "aa2", name: "Sally", gradeLevel: 12, studyHours: 4),
Student(id: "aa3", name: "Susy", gradeLevel: 11, studyHours: 3),
Student(id: "aa4", name: "Billy", gradeLevel: 12, studyHours: 5),
Student(id: "aa5", name: "Jimmy", gradeLevel: 11, studyHours: 1),
Student(id: "aa6", name: "Johnny", gradeLevel: 10, studyHours: 3),
Student(id: "aa7", name: "Mikey", gradeLevel: 12, studyHours: 2),
]
}
}
struct StudyTotals: View {
@ObservedObject var students = GetStudents()
var onlyUpperClass: Bool
var studentsFiltered: [Student] {
switch self.onlyUpperClass {
case true: return students.items.filter {$0.gradeLevel == 11 || $0.gradeLevel == 12 }
case false: return students.items
}
}
var body: some View {
var myArray = getCalcTotals(students: studentsFiltered)
var rows: Array<String> = []
return VStack {
Text("Push Calculated Rows Here??? ")
}.padding()
}
}
struct ContentView: View {
@State private var onlyUpperClass: Bool = false
var body: some View {
return VStack {
StudyTotals(onlyUpperClass: self.onlyUpperClass)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
func getCalcTotals(students: Array<Student>) -> Array<String> {
let studentArray = students.reduce({ /* here */ })
var grade: String
var gradeCount: Int
var gradeHours: Double? = 0
var gradeAvg: Double? = 0
let myArray = ["Count", "Total", "Average"]
return myArray
}
我需要的是这个:
解决方案
您可以ForEach
像在 JavaScript 中一样计算里面的值
struct StudyTotals: View {
@ObservedObject var students = GetStudents()
var onlyUpperClass: Bool
var studentsFiltered: [Student] {
switch self.onlyUpperClass {
case true: return students.items.filter {$0.gradeLevel == 11 || $0.gradeLevel == 12 }
case false: return students.items
}
}
var body: some View {
var countTotal = self.studentsFiltered.count
var hoursTotal = self.studentsFiltered.reduce(0) { $0 + $1.studyHours }
return List {
Group {
HStack {
Text("Count")
Text("Hours")
Text("Avg")
}
ForEach(9...12, id: \.self) { gradeLevel -> AnyView in
let count = self.studentsFiltered.filter{ $0.gradeLevel == gradeLevel }.count
let hours = self.studentsFiltered.filter{ $0.gradeLevel == gradeLevel }.reduce(0) { $0 + $1.studyHours }
let avg = Float(hours) / Float(count)
countTotal += count
hoursTotal += hours
return AnyView(HStack {
Text("Grade\(gradeLevel)")
Text("\(count)")
Text("\(hours)")
Text("\(avg)")
})
}
HStack {
Text("TOTALS")
Text("\(countTotal)")
Text("\(hoursTotal)")
Text("\(Float(hoursTotal) / Float(countTotal))")
}
}
}.padding()
}
}
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