One-time application record of Kotlin type safety builder

In the relevant application framework guided by Android, a Resource class is used to represent the status and results of network requests.

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

In most cases, we use it in activity

private val testViewModel : TestViewModel by viewModels()

private fun getUserInfo(uid: String) {
 (this, Observer {
  when () {
    -> TODO()
    -> TODO()
    -> TODO()
  }
 })
 (uid)
}

I feel so annoying to write too much like this. Every time I do it when(). Is there any more fun writing? For example?

private fun getUserInfo(uid: String) {
 (this, Observer {
  success {
   
  }
  error {
   
  }
  loading {
   
  }
 })
 (uid)
}

When I just need to deal with success, I can not write error/loading.

kotlin's type safety builder can do it, let's take a look at the official example

class HTML {
 fun body() { …… }
}

fun html(init: HTML.() -&gt; Unit): HTML {
 val html = HTML() // Create a receiver object ()  // Pass the recipient object to the lambda return html
}

html {  // The lambda with the receiver starts from this body() // Call a method of the receiver object}

Let’s analyze first, what we need is an object that implements the Observer interface.

So we first define a class to implement the Observer interface

class ResourceObserver<T: Any> : Observer<Resource<T>> {
 override fun onChanged(t: Resource<T>) {
  when(t) {
   is  -> TODO()
   is  -> TODO()
   is  -> TODO()
  }
 }
}

Implement a top-level function and return a ResourceObserver object

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

Call this function to get the ResourceObserver object

resourceObserver {
 //Can call member functions in the object here}

So my implementation is

class ResourceObserver<T: Any> : Observer<Resource<T>> {
 private var success: (<T>.() -> Unit)? = null
 private var error: (.() -> Unit)? = null
 private var loading: (<T>.() -> Unit)? = null
 
 fun success(s: (<T>.() -> Unit)) {
  success = s
 }
 
 fun error(e: .() -> Unit) {
  error = e
 }
 
 fun loading(l: <T>.() -> Unit) {
  loading = l
 }
 
 override fun onChanged(t: Resource<T>) {
  when(t) {
   is  -> success?.invoke(t)
   is  -> error?.invoke(t)
   is  -> loading?.invoke(t)
  }
 }
}

Summarize

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