C#: Trying to use control elements in different class - "object reference is required"

Question

I am brand new to C# (I apologise if my question is noobish - I'm teaching myself, so it's a bumpy process). I am trying to develop a winform and since some of the methods are pretty long, I am trying to keep it in a couple classes. This is what I'm kind of hoping to achieve:

public partial class formMainForm : Form
{
    public formMainForm()
    {
        InitializeComponent(); 
    }

    private void UpDown1_ValueChanged(object sender, EventArgs e)
    {
        longCalculations.LongMethod1(); 
    }
}

public class longCalculations
{
    private void LongMethod1()
    {
        // Arbitrarily long code goes here
    }
}

I'm doing this in an attempt to keep the formMainForm class tidy and be able to split any calculations into manageable chunks. However, I'm encountering problems with using form controls (e.g. check boxes, numeric up-down controls, etc.) in my non-form classes.

If I leave them as is (e.g. CheckBox1) I get a the name does not exist in the current context error. I searched around and I found that it's because that box is defined in a different class. However, if I change it to formMainForm.CheckBox1, the error is now an object reference is required for the non-static field, method or property. Again, I looked around and it appears that that is due to the form initialization method not being static.

If I change public formMainForm() to static formMainForm(), the error now moves to InitializeComponent(); and I do not know where to go from here. I also tried making an instantiation of the formMainForm() method, but that didn't do anything (the code I attempted to use is below. I found it somewhere on this site as an answer to a similar problem).

private void formLoader(object sender, EventArgs e)
{
    shadowrunMainForm runForm = new shadowrunMainForm();
    runForm.Show();
}

How can I use the formcontrol names in other classes?

P.S. It is my first post here - I am super sorry if I have missed this question already being asked somewhere. I did search, but I didn't find what I was looking for.

EDIT

It seems I hadn't made myself clear - this was just an example of code and my problem is with the second class, not the first one. I have now simplified the code to:

public partial class formMainForm : Form
{
    public formMainForm()
    {
        InitializeComponent(); 
    }
}

public class longCalculations
{
    private void LongMethod1()
    {
        List<CheckBox> listOfBoxes = new List<CheckBox>();
        listOfBoxes.Add(CheckBox1);
        // The code displays an "object reference is required for the non-static field, method or property" error at this stage. Changing the "CheckBox1" to formMainForm.CheckBox1 doesn't help
        // Arbitrarily long code goes here
    }
}

LongMethod1 works perfectly fine when placed in the formMainForm partial class. Moving it to the other form makes it unable to take data from those checkboxes.

Answer 1

Ideally, your longCalculations class would not attempt to modify the form directly. Instead it would return an object that the form could use to update its controls.

If you need to access the form directly from the longCalculations class, first change the method to accept an instance of your form

public void LongMethod1(formMainForm myForm)

Then you can pass the form itself as a parameter

var calc = new longCalculations();
calc.LongMethod1(this);

Answer 2

I believe this line longCalculations.LongMethod1(); is throwing error cause you are trying to access a instance method as if it's a static method and as well it's defined as private method which won't be accessible outside the class. You need to create an instance of longCalculations class before accessing any of it's member or method(s) and mark the method public like

private void UpDown1_ValueChanged(object sender, EventArgs e)
{
    longCalculations ln = new longCalculations();
    ln.LongMethod1(); 
}

public class longCalculations
{
    public void LongMethod1()
    {
        // Arbitrarily long code goes here
    }
}

(OR) If you really want it to be a static method then define accordingly with static modifier like

public class longCalculations
{
    public static void LongMethod1()
    {
        // Arbitrarily long code goes here
    }
}

Now you can call it like the way you are trying

Answer 3

public static class longCalculations
{
    public static void LongMethod1()
    {
        // Arbitrarily long code goes here
    }
}

If you're going to make a call longCalculations.LongMethod1();, then you need to make your class static as such.

Or you leave it as not static method by calling

longCalculations lc = new longCalculations()
lc.LongMethod1();

As for accessing controls in separate classes, you can pass in the form and make the controls public which can be dangerous.

So on your Form.designer.cs, change any control you may have to public modifier. Then you would make a call like this...

private void UpDown1_ValueChanged(object sender, EventArgs e)
{
    longCalculations.LongMethod1(this); 
}

public void LongMethod1(Form1 form)
{
    // Arbitrarily long code goes here
    form.label1.Text = someString;
    //more settings and whatnot
}

Or do something like this:

public class longCalculations
{
    public string LongMethod1()
    {
        // Arbitrarily long code goes here

        return myString;
    }
}

longCalculations lc = new longCalculations()
string result = lc.LongMethod1();
this.label1.Text = result;

Answer 4

In your other class, you need to have an instance of your formMainForm class:

var myForm = new formMainForm();

Then you can access its members like this:

myForm.CheckBox1.Checked = true;