2017/10/26 Android Taipei 分享 透過 Data Model 的演進，了解 Kotlin 的優點，並開始導入 Kotlin 現今 Data Model 的趨勢為以下三點: 1. 自動產生 (Code Generation) 2. Immutable Object 3. Null-safety 了解如何透過 Kotlin Data Classes 達到以上三點要求 Demo Project https://github.com/ch8908/KotlinDataClass

1. Kotlin Data Model
黃千碩 (Kros)
oSolve, Ltd./打⼯工趣
Mobile App Developer

2. Outline
• Android data model 演化史
• Kotlin 介紹
• Kotlin classes/data classes 介紹
• Kotlin companion object 介紹
• Unit testing
• What’s next?

3. Data Model 演化史
• 當第⼀一次在 Android 上寫 data model 時

4. Data Model 演化史
• 定義 property

5. public class User {
private String name;
private String email;
private int age;
private Date createdAt;
}

6. Data Model 演化史
• 定義 property
• ⼿手動實作 get, set

7. Data Model 演化史
• 定義 property
• ⼿手動實作 get, set

8. Data Model 演化史
• 定義 property
• ⼿手動實作 get, set
• IDE 可以幫忙產⽣生 setter, getter

9. Data Model 演化史
• 定義 property
• ⼿手動實作 get, set
• IDE 可以幫忙產⽣生 setter, getter, equal, hash, toString

10. public class User implements Parcelable {
private String name;
private String email;
private int age;
private Date createdAt;
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (email != null ? email.hashCode() : 0);
result = 31 * result + age;
result = 31 * result + (createdAt != null ? createdAt.hashCode() : 0);
return result;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (age != user.age) return false;
if (name != null ? !name.equals(user.name) : user.name != null) return false;
if (email != null ? !email.equals(user.email) : user.email != null) return false;
return createdAt != null ? createdAt.equals(user.createdAt) : user.createdAt == null;
}
@Override
public String toString() {
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", age=" + age +
", createdAt=" + createdAt +
'}';
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}

11. Parcelable
• 遇到 parcelable

12. Parcelable
• 遇到 parcelable
• ⼿手動實作

13. Parcelable
• 遇到 parcelable
• ⼿手動實作

14. Parcelable
• 遇到 parcelable
• ⼿手動實作
• ⽤用 android studio plugin 產⽣生 parcelable 實作

15. public class User implements Parcelable {
private String name;
private String email;
private int age;
private Date createdAt;
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (email != null ? email.hashCode() : 0);
result = 31 * result + age;
result = 31 * result + (createdAt != null ? createdAt.hashCode() : 0);
return result;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (age != user.age) return false;
if (name != null ? !name.equals(user.name) : user.name != null) return false;
if (email != null ? !email.equals(user.email) : user.email != null) return false;
return createdAt != null ? createdAt.equals(user.createdAt) : user.createdAt == null;
}
@Override
public String toString() {
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", age=" + age +
", createdAt=" + createdAt +
'}';
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}
@Override
public int describeContents() { return 0; }
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.name);
dest.writeString(this.email);
dest.writeInt(this.age);
dest.writeLong(this.createdAt != null ? this.createdAt.getTime() : -1);
}
public User() {}
protected User(Parcel in) {
this.name = in.readString();
this.email = in.readString();
this.age = in.readInt();
long tmpCreatedAt = in.readLong();
this.createdAt = tmpCreatedAt == -1 ? null : new Date(tmpCreatedAt);
}
public static final Creator<User> CREATOR = new Creator<User>() {
@Override
public User createFromParcel(Parcel source) {return new User(source);}
@Override
public User[] newArray(int size) {return new User[size];}
};

16. public class User implements Parcelable {
private String name;
private String email;
private int age;
private Date createdAt;
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (email != null ? email.hashCode() : 0);
result = 31 * result + age;
result = 31 * result + (createdAt != null ? createdAt.hashCode() : 0);
return result;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (age != user.age) return false;
if (name != null ? !name.equals(user.name) : user.name != null) return false;
if (email != null ? !email.equals(user.email) : user.email != null) return false;
return createdAt != null ? createdAt.equals(user.createdAt) : user.createdAt == null;
}
@Override
public String toString() {
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", age=" + age +
", createdAt=" + createdAt +
'}';
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}
@Override
public int describeContents() { return 0; }
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.name);
dest.writeString(this.email);
dest.writeInt(this.age);
dest.writeLong(this.createdAt != null ? this.createdAt.getTime() : -1);
}
public User() {}
protected User(Parcel in) {
this.name = in.readString();
this.email = in.readString();
this.age = in.readInt();
long tmpCreatedAt = in.readLong();
this.createdAt = tmpCreatedAt == -1 ? null : new Date(tmpCreatedAt);
}
public static final Creator<User> CREATOR = new Creator<User>() {
@Override
public User createFromParcel(Parcel source) {return new User(source);}
@Override
public User[] newArray(int size) {return new User[size];}
};
隨隨便便便便就超過 100 ⾏行行

17. Parcelable
• 遇到 parcelable
• ⼿手動實作
• ⽤用 plugin 產⽣生 Parcelable 實作
• 當 class 越來來越多，property 越來來越多，開發的⼈人越來來越多
• 每次實作就成了了問題

18. 願望
• 如果可以這⼀一切可以⾃自動產⽣生就好！

19. Libraries
• Google AutoValue
https://github.com/google/auto
• Lombok
https://github.com/rzwitserloot/lombok

20. AutoValue
• 只要定義好 interface，就會⾃自動產⽣生 model
• ⾃自動產⽣生 setter, getter, equal, hash, toString
• 有 plugin ⾃自動產⽣生 parcelable 實作
• Builder pattern

21. @AutoValue
public abstract class User implements Parcelable {
public abstract String name();
@Nullable
public abstract String email();
public abstract int age();
public abstract Date createdAt();
public static User create(String name, String email, int age, Date createdAt) {
return builder()
.name(name)
.email(email)
.age(age)
.createdAt(createdAt)
.build();
}
public static Builder builder() {return new AutoValue_User.Builder();}
@AutoValue.Builder
public abstract static class Builder {
public abstract Builder name(String name);
public abstract Builder email(String email);
public abstract Builder age(int age);
public abstract Builder createdAt(Date createdAt);
public abstract User build();
}
}

22. AutoValue
• 除此之外，加入兩兩個概念念：
• Immutable Object: 預設產⽣生的 object 都是 value object，沒有
setter，只有 getter
• Null-safety: 每個 property 都需定義 NonNull, Nullable

23. @AutoValue
public abstract class User implements Parcelable {
public abstract String name();
@Nullable
public abstract String email();
public abstract int age();
public abstract Date createdAt();
public static User create(String name, String email, int age, Date createdAt) {
return builder()
.name(name)
.email(email)
.age(age)
.createdAt(createdAt)
.build();
}
public static Builder builder() {return new AutoValue_User.Builder();}
@AutoValue.Builder
public abstract static class Builder {
public abstract Builder name(String name);
public abstract Builder email(String email);
public abstract Builder age(int age);
public abstract Builder createdAt(Date createdAt);
public abstract User build();
}
}

24. Kotlin 介紹
val name: String = "Android"

25. Kotlin 介紹
val name: String = "Android"
val email: String? = null

26. Kotlin 介紹
val name: String = "Android"
val email: String? = null
var name: String = "Android"

27. Kotlin 介紹
val name: String = "Android"
val email: String? = null
var name: String = "Android"
name = "Android Taipei"

28. Kotlin 介紹
val name: String = "Android"
val email: String? = null
var name: String = "Android"
name = "Android Taipei"
• val: Assign-once (read-only) local variable
• var: Mutable variable:

29. Kotlin 介紹
fun doSomething(name: String) : String {
return name.toUpperCase()
}

30. Classes
• 如何定義⼀一個 class

31. class User {
}

32. class User constructor(
name: String,
email: String?,
age: Int,
createdAt: Date
) { }
• 定義 constructor

33. class User(
name: String,
email: String?,
age: Int,
createdAt: Date
) { }
• 可以省略略關鍵字

34. class User(
name: String,
email: String?,
age: Int,
createdAt: Date
) {
var name: String = name,
var email: String? = email,
var age: Int = age,
var createdAt: Date = createdAt
}
• 定義 properties

35. class User(
var name: String,
var email: String?,
var age: Int,
var createdAt: Date
) { }
• 更更簡單的寫法

36. class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) { }
• 定義 immutable properties

37. class User(
val name: String = "No Name",
val email: String? = null,
val age: Int = 0,
val createdAt: Date = Date()
) { }
• 給預設值

38. Data Classes
• The compiler automatically derives the following members from all
properties declared in the primary constructor:
• 根據你定義的 properties，⾃自動幫你產⽣生以下四種內容
• equals()/hashCode()
• toString()
• componentN() functions
• copy()

39. Data Classes
• Primary constructor ⾄至少要有⼀一個參參數
• 參參數只能是 val, var

40. class User (
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) { }

41. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) { }

42. Parcelable
• 當然也有開發者提供 parcelable 的 plugin，⾃自動產⽣生 parcelable 實作

43. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) { }

44. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) : AutoParcelable { }

45. 演化比較

46. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) : AutoParcelable { }
public class User implements Parcelable {
private String name;
private String email;
private int age;
private Date createdAt;
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (email != null ? email.hashCode() : 0);
result = 31 * result + age;
result = 31 * result + (createdAt != null ? createdAt.hashCode() : 0);
return result;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
if (age != user.age) return false;
if (name != null ? !name.equals(user.name) : user.name != null) return false;
if (email != null ? !email.equals(user.email) : user.email != null) return false;
return createdAt != null ? createdAt.equals(user.createdAt) : user.createdAt == null;
}
@Override
public String toString() {
return "User{" +
"name='" + name + ''' +
", email='" + email + ''' +
", age=" + age +
", createdAt=" + createdAt +
'}';
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}
@Override
public int describeContents() { return 0; }
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.name);
dest.writeString(this.email);
dest.writeInt(this.age);
dest.writeLong(this.createdAt != null ? this.createdAt.getTime() : -1);
}
public User() {}
protected User(Parcel in) {
this.name = in.readString();
this.email = in.readString();
this.age = in.readInt();
long tmpCreatedAt = in.readLong();
this.createdAt = tmpCreatedAt == -1 ? null : new Date(tmpCreatedAt);
}
public static final Creator<User> CREATOR = new Creator<User>() {
@Override
public User createFromParcel(Parcel source) {return new User(source);}
@Override
public User[] newArray(int size) {return new User[size];}
};
@AutoValue
public abstract class User implements Parcelable {
public abstract String name();
@Nullable
public abstract String email();
public abstract int age();
public abstract Date createdAt();
public static User create(String name, String email, int age, Date createdAt) {
return builder()
.name(name)
.email(email)
.age(age)
.createdAt(createdAt)
.build();
}
public static Builder builder() {return new AutoValue_User.Builder();}
@AutoValue.Builder
public abstract static class Builder {
public abstract Builder name(String name);
public abstract Builder email(String email);
public abstract Builder age(int age);
public abstract Builder createdAt(Date createdAt);
public abstract User build();
}
}

47. Copy
• 很多時候我們會更更新 object 內容
• 如何更更新⼀一個 immutable object？
• 利利⽤用 copy()

48. class User(
val name: String,
val email: String?
) {
}

49. class User(
val name: String,
val email: String?
) {
fun copy(name: String = this.name, email: String? = this.email): User {
return User(name = name, email = email)
}
}
• copy() 的實作如下

50. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) : AutoParcelable { }

51. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) : AutoParcelable {
fun updateAge(newAge: Int): User {
return copy(age = newAge)
}
}

52. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) : AutoParcelable {
fun updateAge(newAge: Int): User {
return copy(age = newAge)
}
}

53. data class User(
val name: String,
val email: String?,
val age: Int,
val createdAt: Date
) : AutoParcelable {
fun updateAge(newAge: Int): User {
return copy(age = newAge)
}
}
user = user.updateAge(18);
assertThat(user.getAge()).isEqualTo(18);

54. Companion Object
• Kotlin 中沒有 static 的概念念，改⽤用 Companion Object

55. Companion Object
• Kotlin 中沒有 static 的概念念，改⽤用 Companion Object
• Static method -> Companion method

56. class User(
val name: String,
val email: String?
) {
}

57. class User(
val name: String,
val email: String?
) {
companion object {
fun myCompanionMethod() {
// ...
}
}
}

58. class User(
val name: String,
val email: String?
) {
companion object {
fun myCompanionMethod() {
// ...
}
}
}
// Java 中使⽤用
User.Companion.myCompanionMethod();

59. Companion Object
• Kotlin 中沒有 static 的概念念，改⽤用 Companion Object
• Static method -> companion method
• 舉例例：ViewModel (MVVM 中的 ViewModel)

60. User user = ... // age = 50
UserViewModel viewModel = createViewModel(user)
viewModel.getAgeString(); // "50 歲"

61. class UserViewModel(
context: Context,
val user: User
) {
}

62. class UserViewModel(
context: Context,
val user: User
) {
val ageString: String
}

63. class UserViewModel(
context: Context,
val user: User
) {
val ageString: String
init {
ageString = context.getString(R.string.age_is, user.age.toString())
}
}

64. class UserViewModel(
context: Context,
val user: User
) {
val ageString: String
init {
ageString = context.getString(R.string.age_is, user.age.toString())
}
}
UserViewModel viewModel = new UserViewModel(context, user);
viewModel.getAgeString(); // “50 歲"

65. Companion Object
• 想要使⽤用 data classes
• 使⽤用 companion method

66. data class UserViewModel(
val user: User,
val ageString: String
) {
}

67. data class UserViewModel(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}

68. data class UserViewModel(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}

69. Private Constructor
• 與 Java 相同，可以 private constructor，讓維護更更容易易

70. data class UserViewModel(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}

71. data class UserViewModel private constructor(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}

72. data class UserViewModel private constructor(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}
// Java 中使⽤用
new UserViewModel();

73. data class UserViewModel private constructor(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}
// Java 中使⽤用
new UserViewModel();

74. data class UserViewModel private constructor(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}
// Java 中使⽤用
new UserViewModel();
UserViewModel viewModel = UserViewModel.Companion.create(context, user);

75. data class UserViewModel private constructor(
val user: User,
val ageString: String
) {
companion object {
fun create(context: Context, user: User): UserViewModel {
val ageString = context.getString(R.string.age_is, user.age.toString())
return UserViewModel(user, ageString)
}
}
}
// Java 中使⽤用
new UserViewModel();
UserViewModel viewModel = UserViewModel.Companion.create(context, user);
viewModel.getAgeString(); // "50 歲"

76. Unit Test
• Kotlin 所有的東⻄西，預設都是 final

77. Unit Test
• Kotlin 所有的東⻄西，預設都是 final
• 當要 Mock (2.0) 時，會出現以下問題：
org.mockito.exceptions.base.MockitoException:
Cannot mock/spy class com.example.kotlindataclass.model.xxx
cannot mock/spy because :
- final class

78. Solution
• 啟動 Mockito 2 的 option 功能
(opt-in mocking of final classes/methods)
• 在路路徑 test/resources/mockito-extensions 底下新增檔案：
org.mockito.plugins.MockMaker
• 檔案內容：
mock-maker-inline

79. Solution

80. 如何開始導入 Kotlin
1.挑選最少⽤用到的 Data Model
2.對此 Data Model 寫測試 (encode/decode)
3.透過 Android Studio Converter (command+shift+a)
4.在⼀一個 commit 裡⼀一次做完 (要反悔悔也容易易)

81. What’s Next
• ViewModel 採⽤用 Kotlin
• Presenter 採⽤用 Kotlin
• Helper 採⽤用 Kotlin
• View 採⽤用 Kotlin
• …

82. What’s Next
• 資料操作
• Collections: List, Set, Map
• map, filter, find…etc.
• more…

83. Using Kotlin for Android today!

84. Reference
• Kotlin Data Classes
https://kotlinlang.org/docs/reference/data-classes.html
• Kotlin 的 data class 會對你的程式產⽣生什什麼樣的化學反應
https://ingramchen.io/blog/2017/06/kotlin-data-class.html
• Kotlin Koans
https://kotlinlang.org/docs/tutorials/koans.html
• Mock the unmockable
https://github.com/mockito/mockito/wiki/What%27s-new-in-
Mockito-2#mock-the-unmockable-opt-in-mocking-of-final-classesmethods