Question

FormCollection fc = Application.OpenForms;

foreach (Form frm in fc)
{
//iterate through
}

OR

Form fc = Application.OpenForms["FORMNAME"]; if (fc != null) fc.Close(); fm.Show();

but non of this works in compact framework 3.5. How can i check if form is already opened in CF 3.5?

Answer 1

As @Barry wrote, you will have to do it yourself. Easiest way is to use a dictionary. Your key can be a form’s type, its name, or whatever you need.

private static readonly Dictionary<string, MyForm> _dict 
    = new Dictionary<string, MyForm>();

public MyForm CreateOrShow(string formName)
{
    Form f = null;
    if (!_dict.TryGetValue(formName, out f))
    {
        f = new MyForm();
        _dict.Add(formName, f);
    } 
    return f;
}

Or, if you want to support multiple form types and want to avoid casting, use a generic method:

private static readonly Dictionary<string, Form> _dict 
    = new Dictionary<string, Form>();

public T CreateOrShow<T>(string formName) where T : Form, new()
{
    Form f = null;
    if (!_dict.TryGetValue(formName, out f))
    {
        f = new T();
        _dict.Add(formName, f);
    }
    return (T)f;
}

public T CreateOrShow<T>(string formName, Func<T> ctor) where T : Form
{
    Form f = null;
    if (!_dict.TryGetValue(formName, out f))
    {
        f = ctor();
        _dict.Add(formName, f);
    }
    return (T)f;
}

There are two generic overloads. One of them is used like this:

// use this if MyFormType has a parameterless constructor
var form = CreateOrShow<MyFormType>("Form1");

or, if you need to pass parameters to your form during init:

// use this if MyFormType accepts parameters in constructor
var form = CreateOrShow<MyFormType>("Form1", () => new MyFormType(someData));