Calendar Filtering In Gridview

 
 
I have 2 dropdownlist and a gridview.  The dropdownlists filter the
gridview, but now I have added two calendars and two textboxes.  After
user makes selections from the calendar the text boxes are populated
with the dates.  How do I add this to the following select parameter so
that the filtering/querying works properly? (what I have here does not
work in terms for the dates, but dropdownlists filter when I remove the
dates section):

<asp:SqlDataSource ID="DATA" runat="server" ConnectionString="<%$ ConnectionStrings:DATA_Connection %>"
 
         SelectCommand="SELECT * FROM [atable] WHERE
(afield=@param1 or
@Param1='Select something' or
((CONVERT(char(10), adate,
101)>=@param3 AND CONVERT(char(10), bdate, 101)<=@param4)) AND
(bfield=@Param2 OR @Param2='Select something' or
((CONVERT(char(10),
adate, 101)>=@param3 AND CONVERT(char(10), bdate, 101)<=@param4))"

             UpdateCommand="Update atable set afield=@afield, bfield=@bfield where id=@ID" >  
             
             <selectParameters>
     <asp:controlparameter name="param1" controlid="DropDownList1" PropertyName="SelectedValue" type="String" />
     <asp:controlparameter name="param2" controlid="DropDownList2" PropertyName="SelectedValue" type="String" />
     <asp:ControlParameter Name="param3" ControlID="Textbox1" PropertyName="Text" Type="string" />
     <asp:ControlParameter Name="param4" ControlID="Textbox2" PropertyName="Text" Type="string" />
     
</selectParameters>