Kotlin类型安全构建器的一次运用记录

// A generic class that contains data and status about loading this data.
sealed class Resource(
 val data: T&＃63; = null,
 val message: String&＃63; = null
) {
 class Success(data: T) : Resource(data)
 class Loading(data: T&＃63; = null) : Resource(data)
 class Error(message: String, data: T&＃63; = null) : Resource(data, message)
}

private val testViewModel : TestViewModel by viewModels()

private fun getUserInfo(uid: String) {
 testViewModel.userInfoData.observe(this, Observer {
  when (it.status) {
   Status.SUCCESS -> TODO()
   Status.ERROR -> TODO()
   Status.LOADING -> TODO()
  }
 })
 testViewModel.setUserId(uid)
}

private fun getUserInfo(uid: String) {
 testViewModel.userInfoData.observe(this, Observer {
  success {
   
  }
  error {
   
  }
  loading {
   
  }
 })
 testViewModel.setUserId(uid)
}

class HTML {
 fun body() { …… }
}

fun html(init: HTML.() -> Unit): HTML {
 val html = HTML() // 创建接收者对象
 html.init()  // 将该接收者对象传给该 lambda
 return html
}

html {  // 带接收者的 lambda 由此开始
 body() // 调用该接收者对象的一个方法
}

class ResourceObserver : Observer> {
 override fun onChanged(t: Resource) {
  when(t) {
   is Resource.Success -> TODO()
   is Resource.Error -> TODO()
   is Resource.Loading -> TODO()
  }
 }
}

fun  resourceObserver(init: ResourceObserver.() -> Unit): ResourceObserver {
 val observer = ResourceObserver()
 observer.init()
 return observer 
}

resourceObserver {
 //在此处可以调用对象内的成员函数
}

class ResourceObserver : Observer> {
 private var success: (Resource.Success.() -> Unit)&＃63; = null
 private var error: (Resource.Error.() -> Unit)&＃63; = null
 private var loading: (Resource.Loading.() -> Unit)&＃63; = null
 
 fun success(s: (Resource.Success.() -> Unit)) {
  success = s
 }
 
 fun error(e: Resource.Error.() -> Unit) {
  error = e
 }
 
 fun loading(l: Resource.Loading.() -> Unit) {
  loading = l
 }
 
 override fun onChanged(t: Resource) {
  when(t) {
   is Resource.Success -> success&＃63;.invoke(t)
   is Resource.Error -> error&＃63;.invoke(t)
   is Resource.Loading -> loading&＃63;.invoke(t)
  }
 }
}