嗨,我是Kotlin世界的新手。我喜欢我目前所看到的,并开始考虑将我们在应用程序中使用的一些库从Java转换为Kotlin。

这些库充满了带有setter、getter和Builder类的pojo。现在我已经在谷歌上找到了在Kotlin中实现Builders的最佳方法,但没有成功。

第二次更新:问题是如何写一个建设者设计模式的一个简单的pojo与一些参数在Kotlin?下面的代码是我尝试编写java代码,然后使用eclipse-kotlin-plugin转换为Kotlin。

class Car private constructor(builder:Car.Builder) {
    var model:String? = null
    var year:Int = 0
    init {
        this.model = builder.model
        this.year = builder.year
    }
    companion object Builder {
        var model:String? = null
        private set

        var year:Int = 0
        private set

        fun model(model:String):Builder {
            this.model = model
            return this
        }
        fun year(year:Int):Builder {
            this.year = year
            return this
        }
        fun build():Car {
            val car = Car(this)
            return car
        }
    }
}

当前回答

我刚刚发现了一个有趣的方法来创建kotlin构建器:

如您所见,moduleBuilder可以用于其他grafana构建。

代码如下:

class Grafana(
    private val module: String,
    private val scene: String,
    private val action: String,
    private val metric: String
) {
    companion object {
        fun build(module: String, scene: String, action: String, metric: String) =
            Grafana(module, scene, action, metric)

        val builder = ::build.curriedBuilder()

        private fun <P1, P2, P3, P4, R> Function4<P1, P2, P3, P4, R>.curriedBuilder() =
            fun(p1: P1) = fun(p2: P2) = fun(p3: P3) = fun(p4: P4) = this(p1, p2, p3, p4)
    }

    fun report() = Unit
}


val moduleBuilder = Grafana.builder("module")
val scene = moduleBuilder("scene")
val gfA = scene("action")("metric")
gfA.report()

val sceneB = moduleBuilder("sceneB")
val gfB = sceneB("action")("metric")
gfB.report()

val gfC = Grafana.builder("xx")("xxx")("xxxx")("xxxx")
gfC.report()

其他回答

class Person(
    val name:String,
    val family:String,
    val age:Int,
    val nationalCode: String?,
    val email: String?,
    val phoneNumber: String?
) {

    // Private constructor
    private constructor(builder: Builder) : this (
        builder.name,
        builder.family,
        builder.age,
        builder.nationalCode,
        builder.email,
        builder.phoneNumber
    )

    // Builder class

    // 1 Necessary parameters in Builder class : name , family
    class Builder(val name :String,val family :String) {

        // 2 Optional parameters in Builder class :
        var age: Int = 0
            private set
        var nationalCode: String? = null
            private set
        var email: String? = null
            private set
        var phoneNumber: String? = null
            private set

        fun age(age: Int) = apply { this.age = age }
        fun nationalCode(nationalCode: String) =
            apply { this.nationalCode = nationalCode }
        fun email(email: String) = apply { this.email = email }
        fun phoneNumber(phoneNumber: String) =
            apply { this.phoneNumber = phoneNumber }

        // 3 Create
        fun create() = Person(this)

    }
}

存取资料:

val firstPerson = Person.Builder(
    name = "Adnan",
    family = "Abdollah Zaki")
    .age(32)
    .email("Adnan9011@gmail.com")
    .phoneNumber("+989333030XXX")
    .nationalCode("04400XXXXX")
    .create()

val secondPerson = Person.Builder(
    name = "Foroogh",
    family = "Varmazyar")
    .create()

上面的答案有一点改变和改进

class MyDialog {
  private var title: String? = null
  private var content: String? = null
  private var confirmButtonTitle: String? = null
  private var rejectButtonTitle: String? = null

  @DrawableRes
  private var icon: Int? = null


  fun show() {
    // set dialog content here and show at the end
  }

  class Builder {
      private var dialog: MyDialog = MyDialog()

      fun title(title: String) = apply { dialog.title = title }

      fun icon(@DrawableRes icon: Int) = apply { dialog.icon = icon }

      fun content(content: String) = apply { dialog.content = content }

      fun confirmTitle(confirmTitle: String) = apply { dialog.confirmButtonTitle = confirmTitle }

      fun rejectButtonTitle(rejectButtonTitle: String) = apply { dialog.rejectButtonTitle = rejectButtonTitle }

      fun build() = dialog
  }
}

和使用

MyDialog.Builder()
        .title("My Title")
        .content("My content here")
        .icon(R.drawable.bg_edittext)
        .confirmTitle("Accept")
        .rejectButtonTitle("Cancel")
        .build()
        .show()

我在Kotlin中实现了一个基本的Builder模式,代码如下:

data class DialogMessage(
        var title: String = "",
        var message: String = ""
) {


    class Builder( context: Context){


        private var context: Context = context
        private var title: String = ""
        private var message: String = ""

        fun title( title : String) = apply { this.title = title }

        fun message( message : String ) = apply { this.message = message  }    

        fun build() = KeyoDialogMessage(
                title,
                message
        )

    }

    private lateinit var  dialog : Dialog

    fun show(){
        this.dialog= Dialog(context)
        .
        .
        .
        dialog.show()

    }

    fun hide(){
        if( this.dialog != null){
            this.dialog.dismiss()
        }
    }
}

最后

Java:

new DialogMessage.Builder( context )
       .title("Title")
       .message("Message")
       .build()
       .show();

科特林:

DialogMessage.Builder( context )
       .title("Title")
       .message("")
       .build()
       .show()

我迟到了。如果我必须在项目中使用Builder模式,我也遇到了同样的困境。后来,经过研究,我意识到这是完全不必要的,因为Kotlin已经提供了命名参数和默认参数。

如果你真的需要实施,Kirill Rakhman的答案是关于如何以最有效的方式实施的可靠答案。您可能会发现另一件有用的事情是https://www.baeldung.com/kotlin-builder-pattern,您可以将其与Java和Kotlin的实现进行比较和对比

一种方法是做以下事情:

class Car(
  val model: String?,
  val color: String?,
  val type: String?) {

    data class Builder(
      var model: String? = null,
      var color: String? = null,
      var type: String? = null) {

        fun model(model: String) = apply { this.model = model }
        fun color(color: String) = apply { this.color = color }
        fun type(type: String) = apply { this.type = type }
        fun build() = Car(model, color, type)
    }
}

使用示例:

val car = Car.Builder()
  .model("Ford Focus")
  .color("Black")
  .type("Type")
  .build()