Question

I know you can pass in an array list of String via intent, but what if it’s an array list of some object that I defined? Say an array list of Bicyles, how do I do this?

Answer 1

You can make your objects implement Parcelable and use putParcelableArrayListExtra. Alternatively, you can serialize your objects in some way and put the byte array of your serialized objects. However, while Serializable is easier to implement, it does not perform as well at run time–requiring all objects to be converted to byte streams and generating lots of temporary objects.

There are a lot of examples of how to implement Parcelable, including several in this thread. If you’re using Kotlin, the easiest is to use the kotlin-parcelize plugin. First, add the following to your module’s build.gradle file:

plugins {
    id 'kotlin-parcelize'
}

Then, make your Bicycle class parcelable:

import kotlinx.parcelize.Parcelize

@Parcelize
class Bicycle(val id: Int, val brand: String): Parcelable

Now you can pass an array list of Bicycle via an intent using putParcelableArrayListExtra:

var bicycles : MutableList<Bicycle> = ...

...

intent.putParcelableArrayListExtra("bicycles",
    bicycles as java.util.ArrayList<out Parcelable>
)

The receiving activity can retrieve the bicycles like this:

var bicycles : List<Bicycle>

list=intent.getParcelableArrayListExtra("bicycles")

If you’re targeting API level 33 or later, you can use:

list=intent.getParcelableArrayListExtra("bicycles", Bicycle)

which has better type safety.