How to set a selecting parameter for an ObjectDataSource

Hi I want to pass a parameter to a dataset in a typed dataset .xsd tableadapter.  So when a user clicks on the button named 'Add' they will see the data associated with 'Add' and when they click on the button named 'Remove' they will see the data associated with 'Remove'  

 <asp:ObjectDataSource ID="ObjectDataSource2" runat="server" OldValuesParameterFormatString="original_{0}" SelectMethod="GetData" TypeName="RapidFire.RFTableAdapters.USP_RD_UPSELL_CALCTableAdapter" OnSelecting="ObjectDataSource2_Selecting">
            <SelectParameters>
                <asp:Parameter Name="action" ConvertEmptyStringToNull="true" Type="String" />
            </SelectParameters>
        </asp:ObjectDataSource>

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So I think I'm supposed to create a 'Selecting' event and do something like this:

protected void ObjectDataSource2_Selecting(object sender, ObjectDataSourceSelectingEventArgs e)
        {
            e.InputParameters[""] = "Add";
        }

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I'm not really sure how to apply logic so when a user presses the add or remove button they are going to get the appropriate data ... any point in the right direction would really be appreciated!