How to filter the Application.OpenForms collection with Linq?

Question

I would like to use Where to filter the Application.OpenForms collection with Linq, and several questions on this site [1] [2] [3] suggest that all I that need in order to do that is access its AllKeys property. However, even when I create a new Windows Forms application, the collection doesn't seem to have this property at all and doesn't compile when I try to use it. What could be the reason?

Answer 1

You have to cast it since FormCollection doesn't implement IEnumerable<T> but only IEnumerable:

var query = Application.OpenForms.Cast<Form>()
    .Where(form => ...);

However, the Form has no AllKeys property. Are you confusing webforms and winforms? In the former there is no Application.OpenForms.