Accessing Form's Controls from another class

Question

I have a windows forms application with some controls added to the designer. When I want to change something (LIKE) enabling a text box from inside the Form1.cs, I simply use:

textBox1.Enabled = true;

but now I have a separated class called class1.cs.

How could I enable textBox1 from a static function class1.cs?

NOTE: I did not try any code because I am totally clueless about doing this.

Answer 1

EDIT: Lot of edit.

public partial class Form1 : Form
{
    // Static form. Null if no form created yet.
    private static Form1 form = null;

    private delegate void EnableDelegate(bool enable);

    public Form1()
    {
        InitializeComponent();
        form = this;
    }

    // Static method, call the non-static version if the form exist.
    public static void EnableStaticTextBox(bool enable)
    {
        if (form != null)
            form.EnableTextBox(enable);
    }

    private void EnableTextBox(bool enable)
    {
        // If this returns true, it means it was called from an external thread.
        if (InvokeRequired)
        {
            // Create a delegate of this method and let the form run it.
            this.Invoke(new EnableDelegate(EnableTextBox), new object[] { enable });
            return; // Important
        }

        // Set textBox
        textBox1.Enabled = enable;
    }
}

Answer 2

This is just another method:

TextBox t = Application.OpenForms["Form1"].Controls["textBox1"] as TextBox;

Answer 3

You can pass the instance of your Form to the class

 MyForm frm = new MyForm();

 MyClass c = new MyClass(frm);

Then your class can take that instance and access the textbox

 public class MyClass
 {

   public MyClass(MyForm f)
   {
      f.TextBox1.Enabled = false;
   }
 }

The design does not look OK

It is better to call the class in your form and based on the value returned, manipulate the textbox

//MyForm Class

 MyClass c = new MyClass();
 c.DoSomethings();
 if(c.getResult() == requiredValue)
   textBox1.enabled = true;
 else
   textBox1.enabled = false;

//MyForm Class ends here

UPDATE

public class Class1
{
   public static int SomeFunction()
   {
      int result = 1;
      return result;
   }

   public static void SomeFunction(out int result)
   {
      result = 1;
   }
}

Usage

if(Class1.SomeFunction() == 1)
   textBox1.Enabled = true;
else
   textBox1.Enabled = false;

OR

int result = 0;
Class1.SomeFunction(out result);

if(result == 1)
   textBox1.Enabled = true;
else
   textBox1.Enabled = false;