How can you pass the state of a variable to a sub-form?

Question

I have a form which contains a bool unitConnected. How can I pass the state of this boolean to a sub-form which I create and open at the press of a button?

Main form code:

// Global variable
public bool unitConnected = false;

private void buttonOpenSubForm_Click(object sender, EventArgs e)
{
    unitConnected = true;

    SubForm subForm= new SubForm();

    if (subForm.ShowDialog(this) == DialogResult.OK)
    {
        // Do something
    }
}

Sub-form code:

private MainForm mainForm = new();

public SubForm()
{
    InitializeComponent();
}

private void SubForm_load(object sender, EventArgs e)
{
    if (mainForm.unitConnected) // Do something
}

Answer 1

Answer by @Jon Skeet (in comments): "You can add a parameter to the constructor, then call new SubForm(this). Or if you only need to know about unitConnected, pass that into the constructor instead."

Sub-form:

private MainForm mainForm = new();

public SubForm(Form1 mainForm)
{
    InitializeComponent();
}

Main form:

public bool unitConnected = false;

private void buttonOpenSubForm_Click(object sender, EventArgs e)
{
    unitConnected = true;

    SubForm subForm= new SubForm(this);

    if (subForm.ShowDialog(this) == DialogResult.OK)
    {
        // Do something
    }
}