The document demonstrates the use of Kotlin collection functions like filter, map, flatMap, groupBy, sortedBy etc on sample data models of Category and Product. It shows how to search for one item, filter, map, group collections and sort data. Advanced techniques include filtering, mapping price with VAT, flattening category subcategories, grouping by category, sorting by price etc.

1. Miracle of stdLib
Pop @ Shopspot
Ju @ Agoda

2. Apply, Also, With, Let, Run

3. Apply, Also, With
fun initTextView(context: Context) {
val tvJAV = TextView(context)
tvJAV.setText(R.string.app_name)
tvJAV.setTextColor(ContextCompat.getColor(context, R.color.colorPrimary))
tvJAV.setOnClickListener {
Toast.makeText(context, "Hello JAV", Toast.LENGTH_SHORT).show()
}
}
Java Style

4. Apply, Also, With
fun initTextView(context: Context) {
val tvJAV = TextView(context).apply {
//this in this block is tvJAV scope
setText(R.string.app_name)
setTextColor(ContextCompat.getColor(context, R.color.colorPrimary))
setOnClickListener {
Toast.makeText(context, "Hello JAV", Toast.LENGTH_SHORT).show()
}
}
}
Apply

5. Apply, Also, With
Also
fun initTextView(context: Context) {
val tvJAV = TextView(context).also {
//it or can assign new name
it.setText(R.string.app_name)
it.setTextColor(ContextCompat.getColor(context, R.color.colorPrimary))
it.setOnClickListener {
Toast.makeText(context, "Hello JAV", Toast.LENGTH_SHORT).show()
}
}
}

6. Apply, Also, With
With
fun initTextView(context: Context) {
val textViewText = with(textView) {
setText(R.string.app_name)
setTextColor(ContextCompat.getColor(context, R.color.colorPrimary))
setOnClickListener{
Toast.makeText(context, "Hello JAV", Toast.LENGTH_SHORT).show()
}
// Last statement is return value
text
}
// textViewText = "Miracle of stdLib"
}

7. Let, Run
fun callApi(callback: ((String) -> Unit)? = null) {
val resultString: String? = "" //TODO: Call API and get String result
if (resultString != null && callback != null) {
callback.invoke(resultString)
}
}
Java Style
fun callApi(callback: ((String) -> Unit)? = null) {
val resultString: String? = ""//TODO: Call API and get String result
resultString?.let { success?.invoke(it) }
// or
resultString?.run { success?.invoke(this) }
}
Kotlin Style

8. Let, Run
fun sumPair() {
val pair: Pair<Int, Int>? = Pair(3, 5)
var sum = if (pair != null) pair.first + pair.second else 0
}
Java Style
fun sumPair() {
val pair: Pair<Int, Int>? = Pair(3, 5)
val sumRun = pair?.run { first + second } ?: 0
// or
val sumLet = pair?.let { it.first + it.second } ?: 0
}
Kotlin Style

9. Quiz ?

10. Delegates

11. Lazy
class FakeFragment : Fragment() {
// This approach can not run cuz ...
val badPreference = context.getSharedPreferences(...)
lateinit var lateInitPreference: SharedPreferences
val lazyPreference: SharedPreferences by lazy { context.getSharedPreferences(...) }
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
lateInitPreference = context.getSharedPreferences(...)
lateInitPreference.getString("LATEINIT_PREFERENCE", ":|")
lazyPreference.getString("LAZY_PREFERENCE", ":)")
}
}

12. Observable
class HelloObservable {
var name by Delegates.observable("time0") { _, old, new ->
println("New $new, Old $old")
}
fun run() {
name = "time1" // New time1, Old time0
name = "time2" // New time2, Old time1
name = "time3" // New time3, Old time2
name = "time5" // New time5, Old time3
name = "time6" // New time6, Old time5
}
}

13. Vetoable
class HelloVetoable {
var age by Delegates.vetoable(0) { _, old, new ->
println("New $new, Old $old")
new < 10
}
fun run() {
age = 1 // age = 1
age = 2 // age = 2
age = 10 // age = 2
age = 1000 // age = 2
}
}

14. Collections

15. Type
val list = listOf(1, 2, 3) // [1, 2, 3]
val set = setOf("Ant", "Bat", "Cat", "Ant", "Bat") // [Ant, Bat, Cat]
val map = mapOf("A" to 1, "B" to 2) // {"A":1, "B":2}
val range = 1..5 // [1, 2, 3, 4, 5]
val rangeChar = 'A'..'C' // ['A', 'B', 'C']
Immutable
val list = mutableListOf("A", "B", "C", "A", "B") // [A, B, C, A, B]
list.add("D") // [A, B, C, A, B, D]
list.add(0, "Z") // [Z, A, B, C, A, B, D]
list.removeAt(1) // [Z, B, C, A, B, D]
val set = mutableSetOf("A", "B", "C", "A", "B") // [A, B, C]
val map = mutableMapOf("A" to 1, "B" to 2) // {"A":1, "B":2}
map.remove("C") // {"A":1, "B":2}
Mutable

16. Extension Function
val list = listOf(1, 2, 3)
list.all { it > 0 } // true
list.any { it < 0 } // false
list.none { it > 5 } // false
list.joinToString("Kotlin") // 1Kotlin2Kotlin3
list.sum() // 6
set.sumBy { it.length } // 9
map.minBy { it.value } // {"A":1}
3 in range // true
range.sum() // 15
// Loop
for (i in 0..list.size - 1) {
list[i]
}
list.forEach { item -> }
list.forEachIndexed { index, item -> }
// Convert Type
list.toSet()
set.toMutableList()
map.toList()
range.toList()

17. Extension Function (Operator/Infix)
val list1 = listOf(1, 2, 3) // [1, 2, 3]
val list2 = listOf(3, 4) // [3, 4]
val listPlus = list1 + list2 // [1, 2, 3, 3, 4]
val listMinus = list1 - list2 // [1, 2]
val listContain = 1 in list1 // true
val listUnion = list1 union list2 // [1, 2, 3, 4]
val listIntersect = list1 intersect list2 // [3]
val listSubtract = list1 subtract list2 // [1, 2]
val listZip = list1 zip list2 // [(1, 3), (2, 4)]
Operator Infix

18. Data Model
data class Category(val id: String,
val name: String,
val subCategoryList: List<Category> = listOf())
data class Product(val id: String,
val name: String,
val description: String,
val price: Double,
val category: Category)

19. Search One Item
private val categoryList = listOf(Category("1", "sport"))
private val productList = listOf(
Product("1", "product1", "description1", 100.0, categoryList[0]),
Product("2", "product2", "description2", 200.0, categoryList[0]),
Product("3", "product3", "description3", 300.0, categoryList[0]),
Product("4", "product4", "description4", 400.0, categoryList[0]),
Product("5", "product5", "description5", 200.0, categoryList[0]),
Product("6", "product6", "description6", 600.0, categoryList[0])
)
fun search_one() {
productList.first() // Product 1
productList.first { it.name == "product20" } // Throw NoSuchElementException
productList.firstOrNull { it.price == 200.0 } // Product 2
productList.firstOrNull { it.price == 1000.0 } // Null
productList.last() // Product 6
productList.lastOrNull { it.price == 200.0 } // Product 5
productList.single() // throw IllegalArgumentException("List has more than one element.")
productList.singleOrNull() // Null
productList.single { it.price == 600.0 } // Product 6
productList.single { it.price == 200.0 } // throw IllegalArgumentException("Collection contains more than one
matching element.")
}

20. Advance
private val categoryList = listOf(
Category("1", "sport1", listOf(
Category("4", "sport4"),
Category("5", "sport5")
)),
Category("2", "sport2", listOf(
Category("6", "sport6")
)),
Category("3", "sport3")
)
private val productList = listOf(
Product("1", "product1", "description1", 100.0,
categoryList[0]),
Product("2", "product2", "description5", 200.0,
categoryList[1]),
Product("3", "product3", "description3", 300.0,
categoryList[2]),
Product("4", "product4", "description4", 400.0,
categoryList[1]),
Product("5", "product5", "description2", 200.0,
categoryList[0]),
Product("6", "product6", "description6", 600.0,
categoryList[2])
)
fun advance_collection() {
productList.filter { it.price > 200.0 } // 3,4,6
productList.filterNot { it.price == 200.0 } //
1,3,4,6
productList.map { it.price * 1.07 } // 107.0, 214.0
,321.0, 428.0, 214.0, 642.0 vat7%
categoryList.flatMap {
it.subCategoryList.map { it.name } // [sport4,
sport5], [sport6], []
} // [sport4, sport5, sport6]
productList.groupBy { it.category } // {cat1:[p1,p5],
cat2:[p2,p4], cat3:[p3,p6]
productList.sortedBy { it.price } //
[p1,p2,p5,p3,p4,p6]
productList.sortedByDescending { it.price }
//[p6,p4,p3,p5,p2,p1]
productList.sortedWith(compareBy(Product::price,
Product::description)) // [p1,p5,p2,p3,p4,p6]
}

21. Quiz ?

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