Kotlin 设计模式-建造者

前言

Ktolin的可以使用DSL方式来创建对象，那么对于设计模式来说，DSL方式创建对象就类似于Java 中使用Builder对象来创建，那么来一段代码看看DSL方式创建对象吧，当然Java也可以调用的哦！

Show me the Code

class UnionBankPay private constructor(val activity: Activity,
                                       val tradeCode: String,
                                       val serverModel: String){
    //私有化构造方法
    private constructor(builder: Builder) : this(builder.activity,
            builder.tradeCode,
            builder.serverModel)

    //伴生对象，对外提供静态的build方法
    companion object {
        fun build(init: Builder.() -> Unit) = Builder(init).build()
    }

    //Builder 内部类
    class Builder private constructor() {
        constructor(init: Builder.() -> Unit) : this() {
            init()
        }

        //属性
        lateinit var activity: Activity
        lateinit var tradeCode: String
        lateinit var serverModel: String

        //DSL赋值方法
        fun activity(init: Builder.() -> Activity) = apply { activity = init() }
        fun tradeCode(init: Builder.() -> String) = apply { tradeCode = init() }
        fun serverModel(init: Builder.() -> String) = apply { serverModel = init() }

        fun build() = UnionBankPay(this)
    }
}

调用

UnionBankPay.build {
         activity { this@MainActivity}
         tradeCode { "123123" }
         serverModel { "00" }
}

或者

UnionBankPay.build {
    activity = this@MainActivity
    tradeCode = "123123" 
    serverModel = "00" 
}