Referencing controls within a class

Question

I would like to know how I would reference a control within a class.

This is a code snippet example:

Would need to create a class fille first, or would I create a class within the main project file?

This is to use and instantiate the class again in future builds.

using [Project_Name].Properties;

public class Control_One
{
	Form1 formOne;
	
	
	public void Output_data_to_text_box()
	{
		Form1 formOne = new Form1;
		formOne.[Name_of_Text_Box_control].Text = "Hello there!";
	}

}

Accepted Answer

When dropping a control on a form, by default the control is private to the form. You can select a control, select properties, select the modifier property and set the value to public which allows you to access the control outside of the form. This technique is usually frown on.

If the control in question is on the form, not in another control like a panel you can use in another form or class.

if (Application.OpenForms[nameof(Form1)].Controls["textBox1"] is not TextBox textBox) return;
textBox.Text = "Hello";
textBox.BackColor = Color.Yellow;

And if the control is in a panel for instance. Add the following class to your project.

public static class ControlExtensions
{
    public static IEnumerable Descendants(this Control control) where T : class
    {
        foreach (Control child in control.Controls)
        {
            if (child is T thisControl)
            {
                yield return (T)thisControl;
            }

            if (child.HasChildren)
            {
                foreach (T descendant in Descendants(child))
                {
                    yield return descendant;
                }
            }
        }
    }
}

Usage from a class or other form.

var tb = ((Form1)Application.OpenForms[nameof(Form1)])
    .Descendants()
    .FirstOrDefault(x => x.Name == "textBox1"); ;
if (tb is null) return;
tb.Text = "Hello";
tb.BackColor = Color.Yellow;

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Referencing controls within a class

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