Question

I have written an extension method which finds a control depending on the Type passed as an indexer to the function. Here is my extension method.

public static T FindControlByType<T>(this Control childCnt, string Id = "")
    {
        foreach (Control item in childCnt.Controls)
        {
            if (item is T)
            {
                if (Id == "")
                {
                    return (T)Convert.ChangeType(item, typeof(T));
                }
                if (item.ID.Contains(Id))
                {
                    return (T)Convert.ChangeType(item, typeof(T));
                }
            }
        }

        //return T 

    }

I want to return control of Type T. How do i achieve this?

Answer 1

If you add a generic constraint to restrict T to be of type Control, then you don’t need the ChangeType calls. The cast is enough.

public static T FindControlByType<T>(this Control childCnt, string id = "") 
    where T : Control
{ 
    foreach (Control item in childCnt.Controls) 
    { 
        if (item is T && ((id == "" || item.ID.Contains(id)))
        { 
            return (T)item; 
        } 
    } 

    return default(T);

}