How to create CustomValidator in code behind

Gary King

If I have a basic page with 2 dropdownlists (myDDL1 and myDDL2).
The Items for the lists are:

myDDL1: "", "Red" and "Blue"
myDDL2: "", "Sky" and "Royal"

If the user selects "Blue", then they should also select a value from myDDL2 (if a value is not selected, then display "Please select a value" next to myDDL2.

If the user selects "Red", then I dont need any validation on myDDL2 (or maybe I should validate that the user has not selected a value from myDDL2?)

I think that what I need is a custom validator which will check if myDDL2 selected text is "Blue" and that a value has been selected on myDDL2 , but I'm not having any luck with coding.

The aspx does not have a custom validator - instead, I would like it to be created within the aspx.cs Page_Load event. Also, I would prefer this to be a server-side validation (although I would consider using client-side).

7 Replies

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Felipe Ramos16y ago
Accepted answer
Gary, it works the same way. The only difference is at what point you create your control.

  CustomValidator custom = new CustomValidator();
   custom.ServerValidate += new ServerValidateEventHandler(custom_ServerValidate);
   this.Controls.Add(custom); // This will add it to the page

You can add it to a table or panel if you wish.
Felipe Ramos16y ago
You can only assign a control to validate to the asp.net validators. You can still have a dynamically generate page, but you will need to create independent validators for each control or a function to validate since you are doing at the server level anyways.

public bool IsValid(DropDowList control, string desireValue)
{
if (control.SelectedValue == desireValue)
return true;
else
return false;
}
Gary King16y ago
OMG - that is way too complex for me to understand :o(

I really cannot even start to figure out how to write my own validation function. Is there really no way that I can use the custom valdiator to achieve the result that I want?

What I am trying achieve is a web page that is completely data driven (from SQL Server).
- The code reads from the database and creates controls (currently DropDownList and Textboxes).
- Some of the DropDownLists are required fields (again, defined in the database) and the code creates RequiredFieldValidators for these.
- The problem that I now have is the some of the DropDownLists should be required fields if a preceeding DDL is a certain value.
  
  For example:
Q1 - Do you develop .NET applications? (Yes/No)
Q2 - Which language do you use? (VB/C#)

Q1 is a required field, but Q2 is only a required field if the answer to Q1 is YES. Hence me looking at the custom validator option - maybe there is a better approach to the problem?
Felipe Ramos16y ago
Gary, I think it would be easier to write your own validator or function instead.

http://msdn.microsoft.com/en-us/library/aa720677(VS.71).aspx
Gary King16y ago
Excellent!
I would now like to improve this by making it dynamic as follows.....

I want to pass values to the custom_ServerValidate function, so that it can be used for various validations. What I would be passing is the first control (XXXX), the value to be evaluated (somevalue), the second control (YYYY) and the value of this to be evaluated (anothervalue).

So what I would end up with is multiple controls on my page (eg, DropDownLists that are created by code) and multiple CustomValidators (again, created by code) - each of which would call the same custom_ServerValidate function. The custom_ServerValidate function would then validate the values of the controls that are passed to it.
Is this possible?

    protected void Page_Load(object sender, EventArgs e)
    {
        CustomValidator objCV = new CustomValidator();
        objCV.ServerValidate += new ServerValidateEventHandler(custom_ServerValidate);
        objCV.ID = "myCV";
        objCV.ErrorMessage = "Custom Validator Message";
        form1.Controls.Add(objCV);
    }

    protected void custom_ServerValidate(object source, ServerValidateEventArgs args)
    {
        if (XXXX.SelectedItem.Text == somevalue)
               if (YYYY.SelectedItem.Text == anothervalue)
                  {
                      args.IsValid = false;
                  }
             else
                      args.IsValid = true;
    }

Note: the values in RED BOLD text are to be passed to the custom_ServerValidate function.
Gary King16y ago
Thanks Filipe, but you missed what is probably the most important part of my question...
The aspx does not have a custom validator control on it (or rather, I do not create the control on the page). What I need is for the Page_Load event to create the control and then set it to validate myDDL2.
So, other than the 2 DDL's, there is nothing on the aspx.
Felipe Ramos16y ago
It would look something like this

aspx page

   onservervalidate="ddlValidator_ServerValidate" />

code behind

   protected void ddlValidator_ServerValidate(object source, ServerValidateEventArgs args)
   {
   if (myDDL1.SelectedItem.Text = "Blue")
   if (myDDL2.SelectedItem.Text = "")
   {
   args.IsValid = false;
   ddlValidator.Text = "Please select a value.";
   }
   else
   args.IsValid = true;
   }