Android Data binding - Error:(119, 29) Identifiers must have user defined types from the XML file. main_radio_subscribe is missing it

As you use View.VISIBLE / View.GONE in your .xml file, you should import the View type by doing adding <import type="android.view.View"/> in the data section like the following:

<data>
    <import type="android.view.View"/>

    <variable
        name="viewModel"
        type="xx.xx.MyViewModel"/>
</data>

Looks like the implicit Attribute listeners use camel case when it is used in the expressions, thanks to this post I figured it out.

<!--Recurring Reminder -->
        <android.support.v7.widget.SwitchCompat
            android:id="@+id/addTodo_switch_remind"
            style="@style/MediumTextViewStyle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/addTodo_space_project"
            android:text="@string/add_todo_remind_label"
            android:textOff="@string/generic_no_text"
            android:textOn="@string/generic_yes_text" />

        <android.support.v4.widget.Space
            android:id="@+id/addTodo_space_remind"
            style="@style/FormsSpacingStyle"
            android:layout_below="@+id/addTodo_switch_remind" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/addTodo_space_remind"
            android:orientation="vertical"
            android:padding="@dimen/grid_box_single"
            android:visibility="@{addTodoSwitchRemind.checked ? View.VISIBLE : View.GONE}">

Documenting for others who have the same issue

Step 1: create BindingAdapter:

@BindingAdapter("android:visibility")
public static void setVisibility(final View view, @IdRes int layourId) {
    SwitchCompat switcher = (SwitchCompat)view.getRootView().findViewById(layourId)
    switcher.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener(){
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked)
        {
            view.setVisibility(isChecked ? View.VISIBLE : View.GONE);
        }
    }
}

Step 2: import R class in databinding data section at you layout.xml:

<data>
     <import type="example.package.R"/>
</data>

Step 3: bind custom view to your switcher like this:

<android.support.v7.widget.SwitchCompat
    android:id="@+id/addTodo_switch_remind"/>

<LinearLayout
    android:visibility="@{R.id.addTodo_switch_remind">