Basic example of using databinding to handle button clicks

_Bind onClick.md

• Use a viewmodel to bind the data
• Bind the Button's onClick method to MainViewModel.handleClick()
• Use a custom @BoundFunction annotation to make the viewmodel code more self-documenting

Code

activity_main.xml

<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="viewModel"
            type="com.n8ebel.databindingsandbox.MainViewModel" />

    </data>

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

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

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text='@{"And here we are binding a simple value like the number " + viewModel.number}'
            />

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

    </LinearLayout>
</layout>

MainActivity.kt

class MainActivity : AppCompatActivity(), ViewModelListener {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main).bindData {
            viewModel = MainViewModel("hello", 5, this@MainActivity)
        }
    }

    // region implements ViewModelListener

    override fun showMessage(message: String) {
        Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
    }

    // endregion implements ViewModelListener
}

MainViewModel.kt

class MainViewModel(msg:String, num:Int, val listener:ViewModelListener) {

    val message = ObservableField<String>(msg)
    val number = ObservableInt(num)

    @BoundFunction
    fun handleClick() {
        listener.showMessage("You Clicked It!!")
    }
}