Question

您好我是Swift的新手，我正在斯坦福大学课程iTunes U上学习。我正在编写一个计算器。课程视频中的讲师具有相同的代码，软件和相同版本的XCode。

以下是ViewController的相关代码：

import UIKit

class ViewController: UIViewController {

    @IBOutlet private weak var display: UILabel!

    private var displayValue: Double {

        get {
            return Double(display.text!)!

        }

        set {
            display.text = String(newValue)

        }
    }

    ...

    private var brain = calculatorBrain()

    @IBAction private func performOperation(sender: UIButton) {
        if userIsInTheMiddleOfTyping {
            brain.setOperand(displayValue)
            userIsInTheMiddleOfTyping = false
        }

        if let mathematicalSymbol = sender.currentTitle {
            brain.performOperation(mathematicalSymbol)
        }
        displayValue = brain.result
    }
}

错误出现在最后一句话中：displayValue = brain.result 这是错误：'CalculatorBrain'类型的值没有值'result'

这是CalculatorBrain代码：

import Foundation

    func multiply(op1: Double, op2: Double) -> Double {
         return op1 * op2 
    } 

    class calculatorBrain {
    private var accumulator = 0.0

    func setOperand(operand: Double) {
        accumulator = operand

    }

    var operations: Dictionary<String,Operation> = [
        "π" : Operation.Constant(M_PI),
        "e" : Operation.Constant(M_E),
        "√" : Operation.UnaryOperation(sqrt),
        "cos" : Operation.UnaryOperation(cos),
        "×" : Operation.BinaryOperation(multiply),
        "=" : Operation.Equals


    ]
    enum Operation {
        case Constant(Double)
        case UnaryOperation((Double) -> Double)
        case BinaryOperation((Double, Double) -> Double)
        case Equals
    }

    func performOperation(symbol: String) {
        if let operation = operations[symbol] {
            switch operation {
            case .Constant(let value): accumulator = value
            case .UnaryOperation(let function): accumulator = function(accumulator)
            case .BinaryOperation(let function):
            case .Equals: break
            }

        }
    } 
}

struct PendingBinaryOperationInfo {
    var BinaryFunction: (Double, Double) -> Double
    var firstOperand: Double 
}

var result: Double { 
    get {
        return 0.0 
    }
}

那么问题是什么？

Answer 1

您需要移动结果声明

var result: Double { 
    get {
        return 0.0 
    }
}

这里，在课堂内部：

class calculatorBrain {

    var result: Double { 
        get {
            return 0.0 
        }
    }


...


}

由于您在CalculatorBrain类之外定义结果，因此您收到错误：

类型值＆＃39; CalculatorBrain＆＃39;没有价值＆＃39;结果＆＃39;

类型的值...没有成员

1 个答案: