Gerva

Gerva is a small and very useful library made for building RecyclerViews using a single, smart generic RecyclerViewAdapter.

Key Features

• Eliminating the need for writing all the boilerplate code involved with RecyclerViewAdapters.
• Making sure the RecyclerViewAdapter is not abused and turned into a massive class containing hundreds of lines of code and business logic.
• Separating UI into small reusable elements, Easy to maintain, extend and bugfix.
• Encapsulates all data binding code into xml files using data binding mechanism.
• Eliminating the need of having more than 1 RecyclerViewAdapter in your project :)

How To Use Gerva?

Let's say we want to show a list of students. The simplest use case would look something like this:

GenericRecyclerViewAdapter(
    listOf(
        Student("1", "will", "Smith", Date(63, 2, 1)),
        Student("2", "Harry", "Potter", Date(72, 11, 3)),
        Student("3", "Dave", "Lawrence", Date(99, 8, 5))
        ...
    )
).also { recyclerView.adapter = it }

Result:

Model

The GenericRecyclerViewAdapter takes in a list of Models, Model is an interface that represents each item of that list.

interface Model: Identifiable {
    fun getViewType(): Int
    fun areItemsTheSame(otherItem: Model): Boolean = this.id == otherItem.id
    fun areContentsTheSame(otherItem: Model): Boolean = this == otherItem
}

data class Student(
    override val id: String,
    val firstName: String,
    val lastName: String,
    val dateOfBirth: Date
    ): Model {
    
    override fun getViewType(): Int = R.layout.item_student
    
    // Checks for same identifier
    override fun areItemsTheSame(otherItem: Model): Boolean = (otherItem as? Student)?.id == this.id
    
    // Checks for same UI data - called only if `areItemsTheSame` returns true
    override fun areContentsTheSame(otherItem: Model): Boolean = this == otherItem
}

In order of getting your Model injected to your layout with DataBinding, You must use a data binding layout and add a variable named model:

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="model"
            type="com.ziv_nergal.gerva.model.Student" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="10dp">
        
        <TextView
            android:id="@+id/firstName"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:text="@{model.firstName}" />
            ...

Now let's say we want to add another view to our list, a card that flips every 3 seconds:

GenericRecyclerViewAdapter(
    arrayListOf(
        Student("1", "Will", "Smith", Date(63, 2, 1)),
        Student("2", "Harry", "Potter", Date(72, 11, 3)),
        Student("3", "Dave", "Lawrence", Date(99, 8, 5)),
        Card()
    ),
    viewHolderFactory = MyViewHolderFactory()
).also { recyclerView.adapter = it }

We use the ViewHolderFactory interface here to tell the adapter that we need a custom viewHolder for the card view:

interface ViewHolderFactory {
    fun createViewHolder(
        parent: ViewGroup,
        viewType: Int
    ): GenericRecyclerViewAdapter.GenericViewHolder?
}

class MyViewHolderFactory : ViewHolderFactory {

    override fun createViewHolder(
        parent: ViewGroup,
        viewType: Int
    ): GenericRecyclerViewAdapter.GenericViewHolder? {

        return when (viewType) {
            R.layout.item_card_view ->
                CardViewHolder(
                    ItemCardViewBinding.inflate(
                        LayoutInflater.from(parent.context),
                        parent,
                        false
                    )
                )
                
            // Returning null will tell the adapter to use the base GenericViewHolder
            else -> null
        }
    }
}

class CardViewHolder(
    override val binding: ItemCardViewBinding
) : GenericRecyclerViewAdapter.GenericViewHolder(binding) {

    override fun bind(model: Model?) {
        super.bind(model)
        flipCard()
    }

    private fun flipCard() {
        val mainHandler = Handler(Looper.getMainLooper())

        mainHandler.post(object : Runnable {
            override fun run() {
                itemView.animate().scaleY(0f).withEndAction {
                    binding.cardContent.rotation += 180f
                    itemView.animate().scaleY(1f).withEndAction {
                        (listener as? Card.Listener)?.onCardFlipped()
                    }
                }
                mainHandler.postDelayed(this, 3000)
            }
        })
    }
}

Result:

One more thing, we now want to create another in our list that when clicked, he shuffles the order of the recyclerView items:

data class Button(
    val title: String,
    val subtitle: String? = null,
    val mainIcon: Int,
    val secondaryIcon: Int? = null
) : Model {

    interface Listener {
        fun onButtonClicked(button: Button)
    }
    
    override val id: String = UUID.randomUUID().toString()

    override fun getViewType(): Int = R.layout.item_button
}

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:bind="http://schemas.android.com/apk/res-auto"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>

        <variable
            name="model"
            type="com.ziv_nergal.gerva.model.Button" />

        <variable
            name="listener"
            type="com.ziv_nergal.gerva.model.Button.Listener" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="@{()-> listener.onButtonClicked(model)}">
        ...

We can create an interface and pass it to the adapter as an Any object. the interface will be later be binded with our layout so we can use it to notify listeners on user interaction with our views. now, in our main activity we implement that interface and pass it to the adapter:

val models = arrayListOf(
    Student("1", "Will", "Smith", Date(63, 2, 1)),
    Student("2", "Harry", "Potter", Date(72, 11, 3)),
    Student("3", "Dave", "Lawrence", Date(99, 8, 5)),
    Card(),
    Button(
        "Shuffle",
        "Click to shuffle",
        R.drawable.ic_baseline_flip_camera_android_24
    )
)

private fun initGenericRecyclerViewAdapter() {
    GenericRecyclerViewAdapter(
        models,
        listener =  this@MainActivity,
        viewHolderFactory = ExampleViewHolderFactory()
    ).also { recyclerView.adapter = it }
}

override fun onButtonClicked(button: Button) {
    (recyclerView.adapter as? GenericRecyclerViewAdapter)?.updateData(models.shuffled())
}

Result:

Installation

• Add the JitPack maven repository to the list of repositories
• Add the dependency information

Gradle example:

allprojects {
   repositories {
       mavenCentral()
       maven { url "https://jitpack.io" }
   }
}

dependencies {
   implementation 'com.github.Ziv-Nergal:Gerva:1.0.3'
}

Requirements

• view & data binding enabled

buildFeatures {
    viewBinding true
    dataBinding true
}

Author

Ziv Nergal, [email protected]

License

Gerva is available under the MIT license. See the LICENSE file for more info.