class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainsBinding
    private lateinit var viewModel: CounterViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //setContentView( R.layout.activity_main)

        binding = DataBindingUtil.setContentView(this, R.layout.activity_mains)
        viewModel = ViewModelProvider(this)[CounterViewModel::class.java]
        binding.viewModel = viewModel
        binding.lifecycleOwner = this

    }
}

class CounterViewModel : ViewModel() {
    private val _counter = MutableLiveData<Int>()
    val counter: LiveData<Int>
        get() = _counter

    init {
        _counter.value = 0
    }

    fun increment() {
        _counter.value = (_counter.value ?: 0) + 1
    }

    fun decrement() {
        _counter.value = (_counter.value ?: 0) - 1
    }
}
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <data>
        <variable
            name="viewModel"
            type="com.wingderm.welcome.CounterViewModel" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="减少"
            android:onClick="@{() -> viewModel.decrement()}" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{viewModel.counter}" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="增加"
            android:onClick="@{() -> viewModel.increment()}" />

    </LinearLayout>
</layout>

运行就报错

               java.lang.NoSuchFieldError: No static field viewModel of type I in class Lcom/wingderm/lasermachpor/BR; or its superclasses (declaration of 'com.wingderm.lasermachpor.BR' appears in /data/app/~~lFztbEUFK57q_Z6uCjqI0g==/com.wingderm.lasermachpor-sUOS8X67QhcY0k4E-rmmNg==/base.apk!classes7.dex)

                at com.wingderm.lasermachpor.databinding.ActivityMainsBindingImpl.setViewModel(ActivityMainsBindingImpl.java:92)

                at com.wingderm.welcome.MainActivity.onCreate(MainActivity.kt:19)