Databinding, MaterialCardView should act like Radiogroup

Question

I am trying to implement two MaterialCardViews that should act like a Radiogroup. So if I click one, the other should be unchecked. I am using viewModel, liveData and custom two-way data binding to save these values for later purpose (sending per email).

I had success writing the .xml and implementing the check logic, but I struggle implementing uncheck logic.

XML, short version for better visibility

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

    <data>
        <variable
            name="vm"
            type="com.example.app.data.viewmodel.EmailViewModel" />
    </data>

        <com.google.android.material.card.MaterialCardView
            android:id="@+id/cardViewOne"
            android:checkable="true"
            android:clickable="true"
            android:focusable="true"
            <!-- Custom Two way databinding -->
            app:state_checked="@={vm.cardOptionOneChecked}"
        </com.google.android.material.card.MaterialCardView>


        <com.google.android.material.card.MaterialCardView
            android:id="@+id/cardViewTwo"
            android:checkable="true"
            android:clickable="true"
            android:focusable="true"
            <!-- Custom Two way databinding -->
            app:state_checked="@={vm.cardOptionTwoChecked}">

        </com.google.android.material.card.MaterialCardView>
</layout>

ViewModel

class EmailViewModel @ViewModelInject constructor(
    @Assisted private val savedStateHandle: SavedStateHandle
) : ViewModel() {

    // Variable for Id = cardViewOne
    val cardOptionOneChecked = MutableLiveData<Boolean>()
    
    // Variable for Id = cardViewTwo
    val cardOptionTwoChecked = MutableLiveData<Boolean>()
}

CardViewAdapter.kt

@BindingAdapter("state_checked")
fun setStateChecked(view: MaterialCardView, liveData: MutableLiveData<Boolean>) {
    if (view.isChecked != liveData.value) {
        liveData.value = view.isChecked
    }
}

@InverseBindingAdapter(attribute = "state_checked")
fun getStateChecked(view: MaterialCardView,): Boolean {
    return view.isChecked
}

// I don't know what logic belongs here to make it work! 
// Current approach just checks the current view and does nothing more. How can I save the last
// checked value?
@BindingAdapter("state_checkedAttrChanged")
fun setCheckedAttrListener(
    view: MaterialCardView,
    attrChange: InverseBindingListener,
) {
    view.apply {
        setOnClickListener { view.isChecked = true }
        setOnCheckedChangeListener { card, isChecked ->
            if (card.isChecked && card != view) {
                card.isChecked = false
            }
        }
        attrChange.onChange()
    }
}

I appreciate every help, thank you very much!

P.S: If there is a better and easier way to achieve this e.g. telling the viewModel from the view to save isChecked, please inform me. MaterialCardView has implemented "isChecked" by default but no logic.

Answer 1

Okay, I've solved the Problem:

First, Change Binding Adapter

I actually don't saw any way to use two-way data binding to achieve the above written case. Here is the new Binding Adapter

// View = Clicked MaterialCard, liveData = value in viewModel
@BindingAdapter("state_checked")
fun setStateChecked(view: MaterialCardView, liveData: MutableLiveData<Boolean>) {
    if (view.isChecked != liveData.value) {
        if (liveData.value != null) {
            view.isChecked = liveData.value!!
        }
    }
}

Second, Change XML Layout, because we don't use two-way data binding anymore

<layout
        xmlns:app="http://schemas.android.com/apk/res-auto">
    
        <data>
            <variable
                name="vm"
                type="com.example.app.data.viewmodel.EmailViewModel" />
        </data>
    
            <com.google.android.material.card.MaterialCardView
                android:id="@+id/cardViewOne"
                android:checkable="true"
                android:clickable="true"
                android:focusable="true"
                <!-- Deleted "=" -->
                app:state_checked="@{vm.cardOptionOneChecked}"
            </com.google.android.material.card.MaterialCardView>
    

            <com.google.android.material.card.MaterialCardView
                android:id="@+id/cardViewTwo"
                android:checkable="true"
                android:clickable="true"
                android:focusable="true"
                <!-- Deleted "=" -->
                app:state_checked="@{vm.cardOptionTwoChecked}">
    
            </com.google.android.material.card.MaterialCardView>
    </layout>

Third, Change viewmodel

class EmailViewModel @ViewModelInject constructor(
    @ApplicationContext context: Context,
    @Assisted private val savedStateHandle: SavedStateHandle
) : ViewModel() {

    val cardOptionOneChecked = MutableLiveData<Boolean>()
    
    val cardOptionTwoChecked = MutableLiveData<Boolean>()

    // Added
     fun firstCardClicked() {
        cardOneChecked.value = true
        cardTwoChecked.value = false
    }

    fun secondCardClicked() {
        cardOneChecked.value = false
        cardTwoChecked.value = true
    }
}

Fourth, add clickListener to XML or Fragment (here Fragment)

cardViewOne.setOnClickListener {
    viewModel.firstCardClicked()
}
cardViewTwo.setOnClickListener {
    viewModel.secondCardClicked()
}

If someone has any questions, just write it in the comments, I will help.