How to create CustomValidator in code behind

Question

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).

Felipe Ramos · 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 Ramos · Answer

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 King · Answer

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 Ramos · Answer

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 King · Answer

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 King · Answer

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 Ramos · Answer

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; }

How to create CustomValidator in code behind

Answers (7)