Question

I have 2 Forms in my app, Form1 and Form2. I want to know if there is a
better way of checking if the form has already been loaded. If the form is
loaded in memory and visible, I want the button to do nothing, if the User
has closed the form it should re-instantiate it.

For more info check my code or comment.. 🙂

public partial class Form1: Form
{
    private Form2 form2;

    public Form1() {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e) {

        if (form2== null) {
            form2= new Form2();
        } else {
            if (form2.has_exited()) { // this is a private property
                                      // that I set when Form2.Closing executes
                form2.Dispose();
                form2= new Form2();
            }
        }
        form2.Show();
    }
}

Answer 1

You don’t need to have Form2 handle the closing event, you can just do it directly from Form1:

private Form2 form2;

private void button1_Click(object sender, EventArgs e)
{
    if (form2 == null)
    {
        form2 = new Form2();
        form2.FormClosed += (_, arg) =>
        {
            form2 = null;
        };
        form2.Show();
    }
    else
    {
        //the other form has been opened and not closed; not sure what you want to do
    }
}

Also note that if a form is shown via Show you don’t need to dispose of it. If you show it via ShowDialog then you do, but when you use the non-modal dialog the system will automatically attach an event handler to the closing event that calls dispose.