This is my Xml code
<Data>
<variable
        name="selectSession"
        type="com.braingroom.user.SessionHandler"/>
<android.support.v7.widget.AppCompatCheckBox
                            android:id="@+id/class_check_box"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:layout_alignParentLeft="true"
                            android:layout_weight="1"
                            android:background="@drawable/checkbox_bg"

android:onCheckedChanged="@{selectSession::checkFullSession}"/>
</Data>

public class SessionHandler {
private final String TAG = "SessionHandler";
MessageHelper messageHelper;

public void checkFullSession(View view, boolean isVisible) {
    Toast toast = Toast.makeText(getApplicationContext(), "checked", Toast.LENGTH_SHORT);
    toast.show();
    Log.d("checked","full session");
}