C#

private void myButton_Click(object sender, EventArgs e)
{
   changeMyButton(false);
   Form2 frm2 = new Form2(this);
   frm2.Show();
}
public void changeMyButton(bool state)
{
   myButton.Enabled = state;
}

Form1 form1Ref;
public Form2(Form1 fRef)
{
   InitializeComponent();
   form1Ref = fRef;
}
private void Form2_FormClosing(object sender, FormClosingEventArgs e)
{
   form1Ref.changeMyButton(true);
}

void myButton_Click(object sender, EventArgs e)
{
    myButton.Enabled = false;
    Form2 frm2 = new Form2();
    frm2.FormClosing += new FormClosingEventHandler(frm2_FormClosing);
    frm2.Show();
}

void frm2_FormClosing(object sender, FormClosingEventArgs e)
{
    myButton.Enabled = true;
}

zafersavas wrote:

What if you have form3, form4 etc.

DaveyM69 wrote:

what if you have multiple objects that need to know that form2 is closing? You'd need to pass every object in the constructor. How can you predetermine how many there will be or what types?

Form1 : is the main form, Form2 and Form3 are declared here.<br />
Form2(Form1 frmRef);<br />
Form3(Form1 frmRef);

zafersavas wrote:

Well, this topic seems going deeper

Mycroft Holmes wrote:

Presumably you could also use the same method for any child form

khuzwayom wrote:

If there is any problem or error on the program, this light/siren device should be automatically set on, the light comes on and the siren makes the siren noise, this is done to alert the administrator of a problem.