kotlin - Parcelable implementations generator

本文摘自——https://kotlinlang.org/docs/tutorials/android-plugin.html

Android Extensions plugin provides Parcelable implementation generator as an experimental feature. To be able to use it, turn on the experimental flag.

How to use

Annotate the class with @Parcelize, and a Parcelable implementation will be generated automatically.

import kotlinx.android.parcel.Parcelize
@Parcelize
class User(val firstName: String, val lastName: String, val age: Int): Parcelable

@Parcelize requires all serialized properties to be declared in the primary constructor. Android Extensions will issue a warning on each property with a backing field declared in the class body. Also, @Parcelize can't be applied if some of the primary constructor parameters are not properties.

If your class requires more advanced serialization logic, you can write it inside a companion class:

@Parcelize
data class User(val firstName: String, val lastName: String, val age: Int) : Parcelable {
    private companion object : Parceler<User> {
        override fun User.write(parcel: Parcel, flags: Int) {
            // Custom write implementation
        }

        override fun create(parcel: Parcel): User {
            // Custom read implementation
        }
    }
}

Supported types

@Parcelize supports a wide range of types:

• primitive types (and their boxed versions);
• objects and enums;
• String, CharSequence;
• Exception;
• Size, SizeF, Bundle, IBinder, IInterface, FileDescriptor;
• SparseArray, SparseIntArray, SparseLongArray, SparseBooleanArray;
• all Serializable (yes, Date is supported too) and Parcelable implementations;
• collections of all supported types: List (mapped to ArrayList), Set (mapped to LinkedHashSet), Map (mapped to LinkedHashMap);
  • Also a number of concrete implementations: ArrayList, LinkedList, SortedSet, NavigableSet, HashSet, LinkedHashSet, TreeSet, SortedMap, NavigableMap, HashMap, LinkedHashMap, TreeMap, ConcurrentHashMap;
• arrays of all supported types;
• nullable versions of all supported types.

Custom Parcelers

Even if your type is not supported directly, you can write a Parceler mapping object for it.

class ExternalClass(val value: Int)

object ExternalClassParceler : Parceler<ExternalClass> {
    override fun create(parcel: Parcel) = ExternalClass(parcel.readInt())

    override fun ExternalClass.write(parcel: Parcel, flags: Int) {
        parcel.writeInt(value)
    }
}

External parcelers can be applied using @TypeParceler or @WriteWith annotations:

// Class-local parceler
@Parcelize
@TypeParceler<ExternalClass, ExternalClassParceler>()
class MyClass(val external: ExternalClass)

// Property-local parceler
@Parcelize
class MyClass(@TypeParceler<ExternalClass, ExternalClassParceler>() val external: ExternalClass)

// Type-local parceler
@Parcelize
class MyClass(val external: @WriteWith<ExternalClassParceler>() ExternalClass)