sap.m.CheckBox binding

I tried to bind a checkBox to an OData field, its type is Edm.Boolean. I can done the binding but it behaves like one-way binding, the chekbox shows the right statement when I ask for the value, but when I change the checkbox from checked to unchecked or vica verse, and save it, it will not update the value of the field.

xml view:

                        <CheckBox id="Seen"
                                  selected="{= ${Seen} === 'true'}" 
                                  text="Seen"
                                  enabled="true" />

However, if I change the value in an input box next to the checkbox it takes effect on the checkbox, but the checkbox can not take effect on the input field...

Input xml:

                    <Input value="{Seen}" valueLiveUpdate="true" />

Am I missing something?

Thank for any help in advance!