初学者的通病

  class ViewController: UIViewController {
//这里没有写输入框 就简单写一下了
    var A:Int = 5
    var B:String = "+"
    var C:Int = 10
    var D:Int?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        if B == "+" {
            D = A + C
        }
        if B == "-" {
            D = A - C
        }
        if B == "*" {
            D = A * C
        }
        if B == "/" {
            D = A / C
        }
        print("结果是:",D!)
        // 结果是:15
    }
}

稍微规范一下代码

class ViewController: UIViewController {
    var numberA:Int = 5
    var strOperate:String = "+"
    var numberB:Int = 10
    var numberResult:Int?

    override func viewDidLoad() {
        super.viewDidLoad()
        switch strOperate {
        case "+":
            numberResult = numberA + numberB
        case "-":
            numberResult = numberA - numberB
        case "*":
            numberResult = numberA * numberB
        case "/":
            if numberB != 0 {
                numberResult = numberA / numberB
            } else {
                numberResult = 0
            }
        default:
            break
        }
        print("结果是:", numberResult!)
        // 结果是:15
    }
}

对业务逻辑进行封装

计算逻辑

class Operation: NSObject {
    class func getResult(numberA:Int, numberB:Int, operate:String) -> Int {
        var  result = 0
        switch operate {
        case "+":
            result = numberA + numberB
        case "-":
            result = numberA - numberB
        case "*":
            result = numberA * numberB
        case "/":
            if numberB != 0 {
                result = numberA / numberB
            } else {
                result = 0
            }
        default:
            break
        }
        return result
    }
}

客户端逻辑

class ViewController: UIViewController {
    var numberA:Int = 5
    var strOperate:String = "+"
    var numberB:Int = 10
    var numberResult:Int?

    override func viewDidLoad() {
        super.viewDidLoad()
        numberResult = Operation.getResult(numberA, numberB: numberB, operate: strOperate)
        print("结果是:", numberResult!)
        // 结果是:15
    }
}

最后

解耦及创建工厂类

运算逻辑父类

class Operation: NSObject {
    private var _numberA:Double = 0
    private var _numberB:Double = 0
    var numberA:Double {
        set{
            _numberA = newValue
        }
        get{
            return _numberA
        }
    }
    
    var numberB:Double {
        set{
            _numberB = newValue
        }
        get{
            return _numberB
        }
    }
    
    func getResult() -> Double {
        var  result:Double = 0
        return result
    }
}

运算符子类逻辑(继承运算逻辑父类)

class OperationAdd: Operation {
    // 加法运算类
    override func getResult()->Double{
        var result:Double = 0
        result = numberA + numberB
        return result
    }
}

class OperationSub: Operation {
    // 减法运算类
    override func getResult() -> Double {
        var result:Double = 0
        result = numberA - numberB
        return result
    }
}

class OperationMul: Operation {
    // 乘法运算类
    override func getResult() -> Double {
        var result:Double = 0
        result = numberA * numberB
        return result
    }
}

class OperationDiv: Operation {
    // 除法运算类
    override func getResult() -> Double {
        var result:Double = 0
        if numberB != 0 {
            result = numberA / numberB
        } else {
            result = 0
        }
        return result
    }
}

工厂类

class OperationFactory {
    static func createOperate(operate:String)->Operation {
        var oper:Operation?
        switch operate {
        case "+":
            oper = OperationAdd()
        case "-":
            oper = OperationSub()
        case "*":
            oper = OperationMul()
        case "/":
            oper = OperationDiv()
        default:
            break
        }
        return oper!
    }
}

客户端代码

class ViewController: UIViewController {
    var oper:Operation?

    override func viewDidLoad() {
        super.viewDidLoad()
        oper = OperationFactory.createOperate("+")
        oper?.numberA = 20
        oper?.numberB = 10
        let result:Double = oper!.getResult()
        print("结果是:", result) 
        // 结果是:30       
    }
}

总结

大家可以看到, 通过四种形态的代码展示了同样的操作,从初学者写出的"简单"代码到将代码规范化,到面向对象思想,最后到考虑到耦合度及创建工厂模式;如果你已经理解第四种形态,那么无论是在某一天我们需要修改加法运算,或者继续添加复杂运算逻辑,再或者修改用户界面, 只需要去相应的类中做出对应的修改即可, 当然你要非得说第一种又简单代码又少这话也没毛病,不过咱学的是设计模式你说是不?

我在写出这篇帖子的时候 只有第三步的水平,不知道大家学习设计模式的时候都在什么水平?目前本人水平有限,此贴仅供自己练手和给觉得自己还有不足的同学参考

@旺仔牛奶
2016年3月28日