Add additional Css class programmatically

Question

I have a textbox with a Css class called 'required'. When a user click a button, I'd like to add additional Css Class to the textbox called 'error' without removing the 'required' class. I want to accomplish this from code-behind.

Neoclassic

This would be much easier with client side code. Is there a specific reason for wanting to do this in the codebehind? – Involved

It's not really that difficult (from a development perspective) from code-behind. But you're right about it being easy on the client side and not requiring a round-trip to the server. – Carinacarinate

@Ken he wants to do this onclick. – Involved

the purpose for this is server side validation – Neoclassic

Ah that clears things up considerable. The best way to do this is to validate the whole form on submit. As a side note you should validate on server and client side. – Involved

Answer 1

You can set the CssClass property of the ASP.NET Textbox control. To add more than one CSS class for an element, just separate it with a space:

MyTextBox.CssClass = "class1 class2";

You can put this in your OnClick event handler:

<asp:TextBox ID="MyTextBox" runat="server" OnClick="MyTextBox_Click" />

Then in code-behind:

void MyTextBox_Click(Object sender, EventArgs e) {
    MyTextBox.CssClass = "class1 class2";
}

Carinacarinate

hah i did not know you could do that. And what if I want to delete the second css class? MyTextBox.CssClass = "class1";?? – Neoclassic

okay but what if I don't know what the other CssClass is. I'll be done with the coding and give the back-end to the designers.. in that case I'll hafta know what the name of the CssClass is. I dont prefer working like this since it's hard coded. Can't i do textbox.cssclas += "class2"; – Neoclassic

Yes, just set the property to the single class. You're really just setting a string value of what will appear in the class attribute for the control. – Carinacarinate

If you do textbox.CssClass += "class2", you'll end up with class1class2 in your class attribute. I would write an AddClass method and a RemoveClass method if you want to make this cleaner. Perhaps as extension methods to the WebControl class. – Carinacarinate

Answer 2

I decided to create extension methods for WebControl to have a generic solution. Here's my code:

public static class WebControlExtensions
{
    public static void AddCssClass(this WebControl control, string cssClass)
    {
        if (string.IsNullOrEmpty(control.CssClass))
        {
            control.CssClass = cssClass;
        }
        else
        {
            string[] cssClasses = control.CssClass.Split(' ');
            bool classExists = cssClasses.Any(@class => @class == cssClass);

            if (!classExists)
            {
                control.CssClass += " " + cssClass;
            }
        }
    }

    public static void RemoveCssClass(this WebControl control, string cssClass)
    {
        if (!string.IsNullOrEmpty(control.CssClass))
        {
            string[] cssClasses = control.CssClass.Split(' ');
            control.CssClass = string.Join(" ", cssClasses.Where(@class => @class != cssClass).ToArray());
        }
    }
}

Akvavit

Answer 3

Here is a way to remove css class using a function. Adding a class would be very similar.

public void RemoveCssClass(string className)
{
    string[] splitClasses = TextButton.CssClass.Split(' ');
    string separator = "";

    foreach (string _class in splitClasses)
    {
        if (_class != className)
        {
            TextButton.CssClass += separator + _class;
            separator = " ";
        }
    }

    if (TextButton.CssClass == className)
        TextButton.CssClass = "";
}

Phototelegraphy

That's pretty bad code. How about something like var lsc = splitClasses.ToList(); lsc.Remove(className); TextButton.CssCLass = String.Join(" ", lsc); – Dibbrun

Answer 4

Here's a simple C# method to add or remove a CssClass into a WebControl...

    public static void SetOrRemoveCssClass( WebControl control, string className, bool adding )
    {
        string[] splitClasses = control.CssClass.Split(' ');

        bool hasNow = splitClasses.Contains( className );
        if ( adding && !hasNow )
        {
            control.CssClass += " " + className;
        }
        else if ( !adding && hasNow )   // remove the CssClass attribute
        {
            control.CssClass = control.CssClass.Replace( className, "");
        }
        control.CssClass = control.CssClass.Replace("  "," ").Trim();
    }

Entomostracan