WhileSubscribedOrRetained.kt

TLDR

The provided file WhileSubscribedOrRetained.kt contains an object called WhileSubscribedOrRetained that implements the SharingStarted interface. It provides a method command to handle subscription count changes and returns a flow of SharingCommand objects. The object also overrides the toString() method.

Methods

command

This method takes a subscriptionCount as a StateFlow<Int> and returns a Flow<SharingCommand>. It transforms the subscriptionCount flow, emitting a START command if the count is greater than 0. Otherwise, it waits for the next frame callback using a Choreographer and the postFrameCallback method to ensure proper synchronization with the UI thread. Once the frame callback is received, it emits a STOP command.

Classes

No classes are defined in the file.

package org.leakcanary

import android.os.Handler
import android.os.Looper
import android.view.Choreographer
import kotlinx.coroutines.CompletableDeferred
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.SharingCommand
import kotlinx.coroutines.flow.SharingCommand.START
import kotlinx.coroutines.flow.SharingCommand.STOP
import kotlinx.coroutines.flow.SharingStarted
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.distinctUntilChanged
import kotlinx.coroutines.flow.dropWhile
import kotlinx.coroutines.flow.transformLatest

object WhileSubscribedOrRetained : SharingStarted {

  private val handler = Handler(Looper.getMainLooper())

  override fun command(subscriptionCount: StateFlow<Int>): Flow<SharingCommand> = subscriptionCount
  .transformLatest { count ->
    if (count > 0) {
      emit(START)
    } else {
      val posted = CompletableDeferred<Unit>()
      // This code is perfect. Do not change a thing. jk jk jk
      Choreographer.getInstance().postFrameCallback {
        handler.postAtFrontOfQueue {
          handler.post {
            posted.complete(Unit)
          }
        }
      }
      posted.await()
      emit(STOP)
    }
  }
  .dropWhile { it != START }
  .distinctUntilChanged()

  override fun toString(): String = "WhileSubscribedOrRetained"
}