g00m / KotlinViewModelExample

This is a small example on how to use ViewModels for your Kotlin RecyclerView.

Kotlin ViewModel Example

This is a small example on how to use ViewModels for your Kotlin RecyclerView.

Gradle

Add the databinding:compiler to your build.gradle. android { dataBinding.enabled = true }

dependencies {
    kapt 'com.android.databinding:compiler:2.3.3'
}

ViewModel

class ViewModel(val initText : String) : BaseObservable() {
    @Bindable var textToDisplay : String? = ""
        set(value) {
            field = value
            notifyPropertyChanged(BR.textToDisplay)
        }

    var count = 0

    init { textToDisplay = initText }

    fun printValue () {
        textToDisplay = initText + " ${++count}"
    }
}

ViewHolder

class BaseViewHolder (view : ViewDataBinding) : RecyclerView.ViewHolder(view.root) {}

BaseAdapter

class BaseViewHolder (val view : ItemViewModelBinding) : RecyclerView.ViewHolder(view.root) {}

    class BaseAdapter(val strings : Array<String>) : RecyclerView.Adapter<BaseViewHolder>() {

        override fun getItemCount(): Int {
            return strings.size
        }

        override fun onBindViewHolder(holder: BaseViewHolder?, position: Int) {
            holder?.view?.viewModel = ViewModel(strings.get(position))
        }

        /**
         * Bind the ViewModel to the ViewHolder
         */
        override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): BaseViewHolder {
            val layoutInflater : LayoutInflater = LayoutInflater.from(parent?.context)

            /**
             * The ItemViewModelBinding will be generated from 'com.android.databinding' for you.
             * It is named after your layout file. In this case after 'R.layout.item_view_model'.
             */
            val binding : ItemViewModelBinding = DataBindingUtil.inflate(layoutInflater, R.layout.item_view_model, parent, false)

            return BaseViewHolder(binding)

    }

}

XML

<data>
    <variable
        name="viewModel"
        type="net.g00m.kotlinviewmodelexample.MainActivity.ViewModel"/>
</data>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:layout_margin="10dp">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@{viewModel.textToDisplay}"
        android:onClick="@{() -> viewModel.printValue()}"/>
</LinearLayout>