databinding 双向绑定类型

官方支持的双向绑定：

• AbsListView android:selectedItemPosition
• CalendarView android:date
• CompoundButton android:checked
• DatePicker android:year, android:month, android:day
• NumberPicker android:value
• RadioGroup android:checkedButton
• RatingBar android:rating
• SeekBar android:progress
• TabHost android:currentTab
• TextView android:text
• TimePicker android:hour, android:minute