WorkManager Data.Builder does not support Parcelable

I'm posting my solution here as I think it might be interesting for other people. Note that this was my first go at it, I am well aware that we could probably improve upon it, but this is a nice start.

Start by declaring an abstract class that extends from Worker like this:

abstract class SingleParameterWorker<T> : Worker(), WorkManagerDataExtender{

    final override fun doWork(): WorkerResult {
        return doWork(inputData.getParameter(getDefaultParameter()))
    }

    abstract fun doWork(t: T): WorkerResult

    abstract fun getDefaultParameter(): T
}

The WorkManagerDataExtender is an interface that has extensions to Data. getParameter() is one of these extensions:

 fun <T> Data.getParameter(defaultValue: T): T {
    return when (defaultValue) {
        is ClassA-> getClassA() as T
        is ClassB-> getClassB() as T
        ...
        else -> defaultValue
    }
}

Unfortunately I was not able to use the power of inlined + reified to avoid all the default value logic. If someone can, let me know in the comments. getClassA() and getClassB() are also extensions on the same interface. Here is an example of one of them:

fun Data.getClassA(): ClassA {
        val map = keyValueMap
        return ClassA(map["field1"] as String,
                map["field2"] as Int,
                map["field3"] as String,
                map["field4"] as Long,
                map["field5"] as String)
    }

fun ClassA.toMap(): Map<String, Any> {
        return mapOf("field1" to field1,
                "field2" to field2,
                "field3" to field3,
                "field4" to field4,
                "field5" to field5)
    }

(Then you can call toWorkData() on the return of this extension, or make it return Data instead, but this way you can add more key value pairs to the Map before calling toWorkData()

And there you go, now all you have to do is create subclasses of the SingleParameterWorker and then create "to" and "from" extensions to Data to whatever class you need. In my case since I had a lot of Workers that needed the same type of POJO, it seemed like a nice solution.

Super easy with GSON: https://stackoverflow.com/a/28392599/5931191

// Serialize a single object.    
public String serializeToJson(MyClass myClass) {
    Gson gson = new Gson();
    String j = gson.toJson(myClass);
    return j;
}
// Deserialize to single object.
public MyClass deserializeFromJson(String jsonString) {
    Gson gson = new Gson();
    MyClass myClass = gson.fromJson(jsonString, MyClass.class);
    return myClass;
}

This solution works without using JSON, and serializes directly to byte array.

package com.andevapps.ontv.extension

import android.os.Parcel
import android.os.Parcelable
import androidx.work.Data
import java.io.*

fun Data.Builder.putParcelable(key: String, parcelable: Parcelable): Data.Builder {
    val parcel = Parcel.obtain()
    try {
        parcelable.writeToParcel(parcel, 0)
        putByteArray(key, parcel.marshall())
    } finally {
        parcel.recycle()
    }
    return this
}

fun Data.Builder.putParcelableList(key: String, list: List<Parcelable>): Data.Builder {
    list.forEachIndexed { i, item ->
        putParcelable("$key$i", item)
    }
    return this
}

fun Data.Builder.putSerializable(key: String, serializable: Serializable): Data.Builder {
    ByteArrayOutputStream().use { bos ->
        ObjectOutputStream(bos).use { out ->
            out.writeObject(serializable)
            out.flush()
        }
        putByteArray(key, bos.toByteArray())
    }
    return this
}

@Suppress("UNCHECKED_CAST")
inline fun <reified T : Parcelable> Data.getParcelable(key: String): T? {
    val parcel = Parcel.obtain()
    try {
        val bytes = getByteArray(key) ?: return null
        parcel.unmarshall(bytes, 0, bytes.size)
        parcel.setDataPosition(0)
        val creator = T::class.java.getField("CREATOR").get(null) as Parcelable.Creator<T>
        return creator.createFromParcel(parcel)
    } finally {
        parcel.recycle()
    }
}

inline fun <reified T : Parcelable> Data.getParcelableList(key: String): MutableList<T> {
    val list = mutableListOf<T>()
    with(keyValueMap) {
        while (containsKey("$key${list.size}")) {
            list.add(getParcelable<T>("$key${list.size}") ?: break)
        }
    }
    return list
}

@Suppress("UNCHECKED_CAST")
fun <T : Serializable> Data.getSerializable(key: String): T? {
    val bytes = getByteArray(key) ?: return null
    ByteArrayInputStream(bytes).use { bis ->
        ObjectInputStream(bis).use { ois ->
            return ois.readObject() as T
        }
    }
}

Add proguard rule

-keepclassmembers class * implements android.os.Parcelable {
  public static final android.os.Parcelable$Creator CREATOR;
}