Swift 将数据从一个函数传递到另一个函数

Question

我有一个小型的 swift 应用程序，其中包含 3 个功能。

getIncData()、getExpData()(从 firebase 获取数据并将其存储在数组中)和 getLeftBudget() 应该从 getIncData() - getExpData()

计算数组的总值

我的代码是这样的

var income = [Double]()
var expenses = [Double]()
var totalIncome: Double = 0
var totalExpenses: Double = 0

func getIncData() {
        let budgetDB = Database.database().reference().child("Income")

        budgetDB.observe(.childAdded) { (snapshot) in

            let snapshotValue = snapshot.value as! Dictionary<String, String>

            let value = snapshotValue["Value"]!

            self.income.append(Double(Int(value)!))

            self.totalIncome = self.income.reduce(0, +)

            self.incomeLabel.text =  "Income: " + String(self.totalIncome) + " €";
        }
    }

func getExpData() {

    let budgetDB = Database.database().reference().child("Expenses")

    budgetDB.observe(.childAdded) { (snapshot) in

        let snapshotValue = snapshot.value as! Dictionary<String, String>

        let value = snapshotValue["Value"]!

        self.expenses.append(Double(value)!)

        self.totalExpenses = self.expenses.reduce(0, +)

        self.expensesLabel.text =  "Expenses: " + String(Double(self.totalExpenses)) + " €";
    }

func getLeftBudget() {
        let budgetLeft = self.totalIncome - self.totalExpenses
        self.budgetMonth.text = "Budget left - \(String(budgetLeft))"
    }

现在 getLeftBudget 中的 self.totalIncome 和 self.totalExpenses 返回 0。从函数中获取数据的最佳方法是什么进入第三个函数以便我可以进行计算？

附言数组中填充了来自 firebase 的数据，计算在 getIncData() 和 getExpData()

中完成

Answer 1

您正在使用 budgetDB.observe 从异步函数获取值。

然后当您调用 getLeftBudget 时，您还没有变量中的值。您应该实现一个完成处理函数。

此代码未经测试，我只是在外出时用记事本适配，但思路就是这样。

var income = [Double]()
var expenses = [Double]()
var totalIncome: Double = 0
var totalExpenses: Double = 0

typealias returnCalc = (Bool) -> Void

func getIncData(completion: @escaping returnCalc) {
    let budgetDB = Database.database().reference().child("Income")

    budgetDB.observe(.childAdded) { (snapshot) in

        let snapshotValue = snapshot.value as! Dictionary<String, String>

        let value = snapshotValue["Value"]!

        self.income.append(Double(Int(value)!))

        self.totalIncome = self.income.reduce(0, +)

        self.incomeLabel.text =  "Income: " + String(self.totalIncome) + " €";
        completion(true)
    }
}

func getExpData(completion: @escaping returnCalc) {

    let budgetDB = Database.database().reference().child("Expenses")

    budgetDB.observe(.childAdded) { (snapshot) in

        let snapshotValue = snapshot.value as! Dictionary<String, String>

        let value = snapshotValue["Value"]!

        self.expenses.append(Double(value)!)

        self.totalExpenses = self.expenses.reduce(0, +)

        self.expensesLabel.text =  "Expenses: " + String(Double(self.totalExpenses)) + " €";
        completion(true)
    }
}

func getLeftBudget() {
    getIncData { (completed) in
        getExpData(completion: { (completed) in
            let budgetLeft = self.totalIncome - self.totalExpenses
            self.budgetMonth.text = "Budget left - \(String(budgetLeft))"
        })
    }
}

你可以稍微插入完成 block 的使用，直接使用函数返回值，避免上下文或全局变量:

var income = [Double]()
var expenses = [Double]()
var totalIncome: Double = 0
var totalExpenses: Double = 0

typealias returnCalc = (Double) -> Void

func getIncData(completion: @escaping returnCalc) {
    let budgetDB = Database.database().reference().child("Income")

    budgetDB.observe(.childAdded) { (snapshot) in

        let snapshotValue = snapshot.value as! Dictionary<String, String>

        let value = snapshotValue["Value"]!

        self.income.append(Double(Int(value)!))

//        self.totalIncome = self.income.reduce(0, +)

        self.incomeLabel.text =  "Income: " + String(self.income.reduce(0, +)) + " €";
        completion(self.income.reduce(0, +))
    }
}

func getExpData(completion: @escaping returnCalc) {

    let budgetDB = Database.database().reference().child("Expenses")

    budgetDB.observe(.childAdded) { (snapshot) in

        let snapshotValue = snapshot.value as! Dictionary<String, String>

        let value = snapshotValue["Value"]!

        self.expenses.append(Double(value)!)

//        self.totalExpenses = self.expenses.reduce(0, +)

        self.expensesLabel.text =  "Expenses: " + String(Double(self.expenses.reduce(0, +))) + " €";
        completion(self.expenses.reduce(0, +))
    }
}

func getLeftBudget() {
    getIncData { (inc) in
        getExpData(completion: { (exp) in
            let budgetLeft = inc - exp
            self.budgetMonth.text = "Budget left - \(String(budgetLeft))"
        })
    }
}