Casting to generic type fails in c#

问题

I'd wish to save some coding by being able to create a dynamic GetControl method. My ideas is something like this

private T GetControl<T>(ASPxGridView control, string element)
{
    var returnedElement = (T)control.FindEditFormTemplateControl(element);
    return returnedElement;
}

Which I call with

var myElement = GetControl<ASPxTextBox>(myGridView, "UserId");

But, this fails miserably:

Cannot convert type 'System.Web.UI.Control' to 'T'

Any advices?

回答1:

Try adding a generic constraint:

private T GetControl<T>(ASPxGridView control, string element) where T : Control
{
    var returnedElement = (T)control.FindEditFormTemplateControl(element);
    return returnedElement;
}

回答2:

You can circumvent type safety by casting via object:

var returnedElement = (T)(object)control.FindEditFormTemplateControl(element);

Furthermore, I would constrain your generic type to Web.UI.Control, if only for the purpose of self-documentation:

private T GetControl<T>(ASPxGridView control, string element)
    where T: System.Web.UI.Control
{
    return (T)control.FindEditFormTemplateControl(element);
}

来源：https://stackoverflow.com/questions/7269967/casting-to-generic-type-fails-in-c-sharp