objcode

@Dao
interface ProductsDao {
   // Because this is marked suspend, Room will use it's own dispatcher
   //  to run this query in a main-safe way.
   @Query("select * from ProductListing ORDER BY dateStocked ASC")
   suspend fun loadProductsByDateStockedAscending(): List<ProductListing>

   // Because this is marked suspend, Room will use it's own dispatcher
   //  to run this query in a main-safe way.
   @Query("select * from ProductListing ORDER BY dateStocked DESC")

objcode

// Solution 0: Disable the sort buttons when any sort is running

class ProductsViewModel(val productsRepository: ProductsRepository): ViewModel() {
   private val _sortedProducts = MutableLiveData<List<ProductListing>>()
   val sortedProducts: LiveData<List<ProductListing>> = _sortedProducts
  
   private val _sortButtonsEnabled = MutableLiveData<Boolean>()
   val sortButtonsEnabled: LiveData<Boolean> = _sortButtonsEnabled
  
   init {

objcode

// Solution #1: Cancel previous work

// This is a great solution for tasks like sorting and filtering that
// can be cancelled if a new request comes in.

class ProductsRepository(val productsDao: ProductsDao, val productsApi: ProductsService) {
   var controlledRunner = ControlledRunner<List<ProductListing>>()

   suspend fun loadSortedProducts(ascending: Boolean): List<ProductListing> {
       // cancel the previous sorts before starting a new one

objcode

// see the complete implementation at
// https://gist.github.com/objcode/7ab4e7b1df8acd88696cb0ccecad16f7
suspend fun cancelPreviousThenRun(block: suspend () -> T): T {
   // If there is an activeTask, cancel it because it's result is no longer needed
   activeTask?.cancelAndJoin()
   
   // ...

objcode

// Solution #2: Add a Mutex

// Note: This is not optimal for the specific use case of sorting
// or filtering but is a good pattern for network saves.

class ProductsRepository(val productsDao: ProductsDao, val productsApi: ProductsService) {
   val singleRunner = SingleRunner()

   suspend fun loadSortedProducts(ascending: Boolean): List<ProductListing> {
       // wait for the previous sort to complete before starting a new one

objcode

class ProductsRepository(val productsDao: ProductsDao, val productsApi: ProductsService) {
   var controlledRunner = ControlledRunner<List<ProductListing>>()

   suspend fun fetchProductsFromBackend(): List<ProductListing> {
       // if there's already a request running, return the result from the 
       // existing request. If not, start a new request by running the block.
       return controlledRunner.joinPreviousOrRun {
           val result = productsApi.getProducts()
           productsDao.insertAll(result)
           result

objcode

// see the complete implementation at
// https://gist.github.com/objcode/7ab4e7b1df8acd88696cb0ccecad16f7#file-concurrencyhelpers-kt-L124

suspend fun joinPreviousOrRun(block: suspend () -> T): T {
    // if there is an activeTask, return it's result and don't run the block
    activeTask?.let {
        return it.await()
    }
    // ...

objcode

#!/usr/bin/env python

from collections import namedtuple

CoC = 0.018 # canon APS-C
MIN_DISTANCE = 100 # must focus 300mm away
MAX_DISTANCE = 1 * 1000 * 1000 # must focus one KM away

FOCALS = [1.3 + (x/10.0) for x in xrange(1, 40 * 10)]
FOCUS_DISTANCE = [100 * x for x in xrange(1, 10)]

objcode

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".AwesomeActivity">


    <Button

objcode

// Using view binding in an Activity
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    val binding = ActivityAwesomeBinding.inflate(layoutInflater)

    binding.title.text = "Hello"
    binding.subtext.text = "Concise, safe code"
    binding.button.setOnClickListener { /* ... */ }

    setContentView(binding.root)