Help Kotlin Help You

Transcript

1. Help otlin Help You @calren24
2. An ‘early’ taste of Kotlin: from Kotlin in Action
3. Data classes Nullability Scope functions Coroutines Dangers of synthetic binding
4. Data classes
5. public class User { private String name; @Nullable private String emailAddress; public User(String name) { … } public User(String name, String emailAddress) { … } public String getName() { … } public void setName(String name) { … } @Nullable public String getEmailAddress() { … } public void setEmailAddress(@Nullable String emailAddress) { … } @Override public String toString() { … } @Override public boolean equals(Object o) { … } @Override public int hashCode() { … } }
6. public class User { private String name; @Nullable private String emailAddress; public User(String name) { … } public User(String name, String emailAddress) { … } public String getName() { … } public void setName(String name) { … } @Nullable public String getEmailAddress() { … } public void setEmailAddress(@Nullable String emailAddress) { … } @Override public String toString() { … } @Override public boolean equals(Object o) { … } @Override public int hashCode() { … } }
7. • Maintaining data classes can be a hassle
8. • Maintaining data classes can be a hassle • Creating objects can be confusing if builder pattern doesn’t exist
 
 new Book("Jane Eyre", "Charlotte Brontë”);
9. • Maintaining data classes can be a hassle • Creating objects can be confusing if builder pattern doesn’t exist
 
 new Book("Jane Eyre", "Charlotte Brontë”); ??? ???
11. public class User { private String name; @Nullable private String emailAddress; public User(String name) { … } public User(String name, String emailAddress) { … } public String getName() { … } public void setName(String name) { … } @Nullable public String getEmailAddress() { … } public void setEmailAddress(@Nullable String emailAddress) { … } @Override public String toString() { … } @Override public boolean equals(Object o) { … } @Override public int hashCode() { … } }
12. data class User (val name: String, var emailAddress: String? = null)
13. data class User (val name: String, var emailAddress: String? = null)
14. • Automatically creates equals() , hashCode(), toString()
 data class User (val name: String, var emailAddress: String? = null)
15. • Automatically creates equals() , hashCode(), toString() • val vs var
 data class User (val name: String, var emailAddress: String? = null)
16. • Automatically creates equals() , hashCode(), toString() • val vs var • denotes nullable fields
 
 val userDroid = User(name = "Droid")
 data class User (val name: String, var emailAddress: String? = null)
17. • Automatically creates equals() , hashCode(), toString() • val vs var • denotes nullable fields
 
 val userDroid = User(name = "Droid") • default values
 data class User( val name: String, var emailAddress: String? = null, var optIntoEmails: Boolean = true )
18. Nullability
19. !! usually signals a code smell and is not as safe as you think
20. !! usually signals a code smell and is not as safe as you think be wary of silent failures using ? 

21. !! usually signals a code smell and is not as safe as you think be wary of silent failures using ? 
 user?.paymentMethod?.executeTransaction()
22. !! usually signals a code smell and is not as safe as you think be wary of silent failures using ? 
 user?.paymentMethod?.executeTransaction() ?: Log.i("TAG", “No payment method stored”)
23. // Java-like if (userDroid.emailAddress != null && userDroid.optIntoEmails) { sendMarketingEmail(userDroid.emailAddress!!) }
24. // Java-like if (userDroid.emailAddress != null && userDroid.optIntoEmails) { sendMarketingEmail(userDroid.emailAddress!!) } // Kotlin-esque userDroid.emailAddress?. takeIf { userDroid.optIntoEmails }?. let { sendMarketingEmail(it) }
25. Scope Functions
26. Functions that allow for changing ‘scope’ of variables Scope Functions
27. Functions that allow for changing ‘scope’ of variables user?.fullName?.let { fullName -> val formattedName = format(fullName) displayGreeting(formattedName) } Scope Functions
28. Functions that allow for changing ‘scope’ of variables also { } apply { } let { } run { } with("an argument") { doSomething(this) } Similar in functionality, differences in appropriate use case Scope Functions
29. Scope Functions From Medium article: Kotlin Demystified - Scope Functions
30. let { }
31. let { } Useful for null check and self-contained variables
32. if (user != null && user.emailAddress != null) { sendMarketingEmail(user.emailAddress!!) } let { }
33. if (user != null && user.emailAddress != null) { sendMarketingEmail(user.emailAddress!!) } user?.emailAddress?.let { sendMarketingEmail(it) } let { }
34. if (user != null && user.emailAddress != null) { sendMarketingEmail(user.emailAddress!!) } user?.emailAddress?.let { sendMarketingEmail(it) } user?.emailAddress?.let { emailAddress -> sendMarketingEmail(emailAddress) } let { }
35. if (user != null && user.emailAddress != null) { sendMarketingEmail(user.emailAddress!!) } user?.emailAddress?.let { sendMarketingEmail(it) } user?.emailAddress?.let { emailAddress -> sendMarketingEmail(emailAddress) } Database.getConnection().let { } // connection doesn't exist outside let { }
36. apply { }
37. apply { } Useful for object configuration
38. val view = View(this).apply { setBackgroundColor() setOnLongClickListener { } setOnClickListener { } } apply { }
39. val view = View(this).apply { setBackgroundColor() setOnLongClickListener { } setOnClickListener { } } val view2 = View(this) view2.setBackgroundColor() view2.setOnLongClickListener { } view2.setOnLongClickListener { } apply { }
40. also { } Useful for calls that need a contextual object, but doesn’t alter the object itself
41. also { } val paint = Paint() .apply { color = Color.BLUE pathEffect = PathEffect() } .also { print("Starting paint with ${it.color}") }
42. run { }
43. run { } Combination of with and let
44. run { } Combination of with and let Useful for initialization
45. run { } val randomWelcomeGreeting = GreetingGenerator.obtain().run { day = getDayOfWeek() mood = Mood.Cheerful voice = Voice.OPRAH generate() }
46. Scope Functions let Executing code with null check 
 Introducing local variables apply Object configuration
 run Top level initialization also Additional effects with Grouping function calls
47. Kotlin Standard Functions Cheat Sheet
48. Coroutines
49. Simplify managing background threads without managing callbacks
50. Simplify managing background threads without managing callbacks Sequential code is a lot easier to read and manage
51. Simplify managing background threads without managing callbacks Sequential code is a lot easier to read and manage
 
 // Async callbacks networkRequest { result -> // Successful network request databaseSave(result) { rows -> // Result saved } }
52. Simplify managing background threads without managing callbacks Sequential code is a lot easier to read and manage
 
 // Async callbacks networkRequest { result -> // Successful network request databaseSave(result) { rows -> // Result saved } } // The same code with coroutines val result = networkRequest() // Successful network request databaseSave(result) // Result saved vs
53. Synthetic Binding
54. import kotlinx.android.synthetic.main. activity_main.*
 
 button.text = "Click me" <TextView 
 android:id="@+id/button"/> Activity.kt activity.xml
55. import kotlinx.android.synthetic.main. activity_main.*
 
 button.text = "Click me" <TextView 
 android:id="@+id/button"/> Activity.kt activity.xml Makes available ALL ids defined in the project
56. import kotlinx.android.synthetic.main. activity_main.*
 
 button.text = "Click me" <TextView 
 android:id="@+id/button"/> Activity.kt activity.xml Makes available ALL ids defined in the project Views unrelated to inflated layout are accessible
57. import kotlinx.android.synthetic.main. activity_main.*
 
 button.text = "Click me" <TextView 
 android:id="@+id/button"/> Activity.kt activity.xml Makes available ALL ids defined in the project Views unrelated to inflated layout are accessible Doesn’t expose nullability well
58. import kotlinx.android.synthetic.main. activity_main.*
 
 button.text = "Click me" <TextView 
 android:id="@+id/button"/> Activity.kt activity.xml Makes available ALL ids defined in the project Views unrelated to inflated layout are accessible Doesn’t expose nullability well Other options: Data Binding or Butter Knife
59. Codelabs
60. Refactoring to Kotlin Using Kotlin Coroutines in your Android app Android Data Binding Room with a View