[SOLVED] MVVM+Kotlin+Databinding best practice

MVVM+Kotlin+Databinding best practice

I am building an app on MVVM+Kotlin+Databinding, and i have this situation i am stuck at. I have LoginFragment which has a phone number edittext and a button, Now i need to check if the phone number is empty or not when user clicks the button. Normally i would do that by using this code in my fragment.

if(!binding!!.phone.text.isEmpty()) {
    //do something
}

But according to experts my view should not know anything about the business logic, Hence i need to have this check inside my viewModel. so what should be the best way to achieve this?

Solution

Here is the bet practice to achieve that (from my point of view):

In your layout add text watcher and text to your EditText

android:text="@{view_model.phone}"
app:addTextChangedListener="@{view_model.phoneWatcher}"

and on click method to your button

android:onClick="@{() -> view_model.save()}"

Inside the ViewModel you will have text observable and a watcher

val phone = ObservableField<String?>()

val phoneWatcher = object : TextWatcherAdapter() {
    override fun afterTextChanged(s: Editable?) {
        phone.set(s?.toString())
    }
}

Now you can make your check inside ViewModel

fun save() {
    if (phone.get()?.isNotEmpty == true) {
        // TODO: do something
    }
}

Also please note that it is a best practice to avoid doing something like that binding!!.phone in Kotlin. If you're using !! to make a possible nullable object look like it is not-nullable (even if you're 100% sure it is) - you're doing something wrong.