Question : Validating dropdownlist cascading.

If you goto omegalove.com/register.aspx
you will see that I have used ajax to populate the

 
 Country   Choose a Country
 State/Province  Choose a Province/State  ==> if it does not exist what should I put.
 City  Choose a City  ==> if it returns nothing what should I populate it with

I have the following if you goto omegalove.com/Register.aspx

I need to make sure a user selects a region if there exist one for that country.
As well as selecting a city if there exist one for that specific region.


At the present moment the user can press the submit button where he/she can goto the
next page in which there was no selection made. What can I do in the code to make sure
this does not occur. Have a message occur? Thanks for helping me.



opDownList>
        Down
                ID="cddCountryRegister"
                runat="server"
                TargetControlID="ddlCountryRegister"
                BehaviorID="myCDECountryRegister"
                Category="Country"
                PromptText="Choose a Country"
                LoadingText="[Loading Countries...]"
                ServicePath="../LocationService.asmx"
                ServiceMethod="GetCountries"
                Enabled="True"
          />

                     ID="ddlRegion" runat="server" ForeColor="Black">opDownList>
               
                Down
                ID="cddRegion"
                runat="server"
                TargetControlID="ddlRegion"
                ParentControlID="ddlCountryRegister"
                Category="Region"
                PromptText="Choose a Province/State"
                LoadingText="Loading Provinces/States..."
                ServicePath="../LocationService.asmx"
                ServiceMethod="GetRegionsForCountry"
     />

           Width="180px" ID="ddlCity" runat="server" ForeColor="Black">opDownList>
          Down
                        ID="cddCity"
                        runat="server"
                        TargetControlId="ddlCity"
                        ParentControlID="ddlRegion"  
                        Category="City"
                        PromptText="Choose a City"
                        LoadingText="Loading Cities..."        
                        ServicePath="../LocationService.asmx"
                        ServiceMethod="GetCityForRegionCountry"
     />

Answer : Validating dropdownlist cascading.

One option is to add Validator controls to your page.  They take care of displaying error messages whenever the validation fails.

Another alternative is to intercept the OnClick event of the Submit button and perform your validation there.  It's simple, you make sure that the SelectedValue of each DropDownList is not empty if the Count of items is greater than one.  I said greater than one because you always leave a comment item in your lists, such as "Select City", even when they are empty.

You could do this also in the Page_Load event of the page.

     -dZ.