行为型模式
在软件工程中， 行为型设计模式是用来确认对象之间的公共的交流模式的。通过这样做，这些模式提高了实现这种交流的灵活性。
举例：
interface TextChangedListener { fun onTextChanged(newText: String)
} class PrintingTextChangedListener : TextChangedListener {
override fun onTextChanged(newText: String) = println("Text is changed to: $newText")
} class TextView { var listener: TextChangedListener? = null
var text: String by Delegates.observable("") { prop, old, new ->
listener?.onTextChanged(new)
}
}输出
Text is changed to: Lorem ipsum Text is changed to: dolor sit amet
策略模式
策略模式一般用来创建一个可替换的算法簇，在运行时决定需要什么。
使用
val lowerCasePrinter = Printer(lowerCaseFormatter)
lowerCasePrinter.printString("LOREM ipsum DOLOR sit amet") val upperCasePrinter = Printer(upperCaseFormatter)
upperCasePrinter.printString("LOREM ipsum DOLOR sit amet") val prefixPrinter = Printer({ "Prefix: " + it })
prefixPrinter.printString("LOREM ipsum DOLOR sit amet")举例：
interface OrderCommand { fun execute()
} class OrderAddCommand(val id: Long) : OrderCommand { override fun execute() = println("adding order with id: $id")
} class OrderPayCommand(val id: Long) : OrderCommand { override fun execute() = println("paying for order with id: $id")
} class CommandProcessor { private val queue = ArrayList<OrderCommand>() fun addToQueue(orderCommand: OrderCommand): CommandProcessor
= apply { queue.add(orderCommand) } fun processCommands(): CommandProcessor = apply {
queue.forEach { it.execute() }
queue.clear()
}
}输出
adding order with id: 1adding order with id: 2paying for order with id: 2paying for order with id: 1
状态模式
状态模式一般用来在对象内部的状态发生改变时，更改这个对象的行为。这个模式允许在运行时显示的更改一个对象的类。
<a target="_blank title=" null"="" href="https://github.com/dbacinski/Design-Patterns-In-Kotlin#example-3" >举例：
sealed class AuthorizationState { class Unauthorized : AuthorizationState() class Authorized(val userName: String) : AuthorizationState()
} class AuthorizationPresenter { private var state: AuthorizationState = Unauthorized() fun loginUser(userLogin: String) {
state = Authorized(userLogin)
} fun logoutUser() {
state = Unauthorized()
} val isAuthorized: Boolean
get() { when (state) { is Authorized -> return true
else -> return false
}
} val userLogin: String get() { when (state) { is Authorized -> return (state as Authorized).userName is Unauthorized -> return "Unknown"
}
} override fun toString(): String { return "User '$userLogin' is logged in: $isAuthorized"
}
}输出
User 'admin' is logged in: trueUser 'Unknown' is logged in: false
责任链模式
责任链模式通常用来处理多变的请求，每个请求可能交由不同的处理者进行处理。
<a target="_blank title=" null"="" href="https://github.com/dbacinski/Design-Patterns-In-Kotlin#example-4" >举例：
interface MessageChain { fun addLines(inputHeader: String): String
} class AuthenticationHeader(val token: String?, var next: MessageChain? = null) : MessageChain { override fun addLines(inputHeader: String): String {
token ?: throw IllegalStateException("Token should be not null") return "$inputHeader Authorization: Bearer $token\n".let { next?.addLines(it) ?: it }
}
} class ContentTypeHeader(val contentType: String, var next: MessageChain? = null) : MessageChain { override fun addLines(inputHeader: String): String
= "$inputHeader ContentType: $contentType\n".let { next?.addLines(it) ?: it }
} class BodyPayload(val body: String, var next: MessageChain? = null) : MessageChain { override fun addLines(inputHeader: String): String
= "$inputHeader $body\n".let { next?.addLines(it) ?: it }
}输出
Message with Authentication:Authorization: Bearer 123456ContentType: json{"username"="dbacinski"}访问者模式
访问者模式通常用来将结构相对复杂的数据类从功能（根据它们所持有的数据来执行）中分离出来。
使用
val projectAlpha = FixedPriceContract(costPerYear = 10000) val projectBeta = SupportContract(costPerMonth = 500) val projectGamma = TimeAndMaterialsContract(hours = 150, costPerHour = 10) val projectKappa = TimeAndMaterialsContract(hours = 50, costPerHour = 50) val projects = arrayOf(projectAlpha, projectBeta, projectGamma, projectKappa) val monthlyCostReportVisitor = MonthlyCostReportVisitor()
projects.forEach { it.accept(monthlyCostReportVisitor) }
println("Monthly cost: ${monthlyCostReportVisitor.monthlyCost}")