Question

I am doing a simple page (Default.aspx), where is a DropDownList (id colors) control. It is easy to populate it with items in PageLoad method.

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        colors.Items.Add("red");
    }
}   etc. ....

However, is it possible to fill the colors control from external class file (I mean some class file located in AppCode folder).

Thanks.

Answer 1

Absolutely. For example, if you just want to create some generic utility method to bind a IEnumerable<T> of values to a DropDownList, you’d pass both of those object as arguments to the method:

public static void BindDropDownControl<T>(DropDownList dropDown, IEnumerable<T> listValues)
{
    // logic to bind the values to the DropDownList
}

What makes this work is the fact that classes like DropDownList are reference types. This means that the instance of dropDown in the method is not a copy of the one form the page, but is instead the same one from the page. So modifications made to it in this method will be applicable to the DropDownList on the page itself.

So to call it from the page, you’d do something like:

if (!this.IsPostBack)
{
    HttpUtils.BindDropDownControl(colors, colorValues);
}

Where colorValues is some list of values to bind to the list. (And HttpUtils is the name of the class containing the above method, but you can name it whatever you want.)