CS0120: An object reference is required for the nonstatic field, method, or property 'foo'

Question

Consider:

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //int[] val = { 0, 0};
            int val;
            if (textBox1.Text == "")
            {
                MessageBox.Show("Input any no");
            }
            else
            {
                val = Convert.ToInt32(textBox1.Text);
                Thread ot1 = new Thread(new ParameterizedThreadStart(SumData));
                ot1.Start(val);
            }
        }

        private static void ReadData(object state)
        {
            System.Windows.Forms.Application.Run();
        }

        void setTextboxText(int result)
        {
            if (this.InvokeRequired)
            {
                this.Invoke(new IntDelegate(SetTextboxTextSafe), new object[] { result });
            }
            else
            {
                SetTextboxTextSafe(result);
            }
        }

        void SetTextboxTextSafe(int result)
        {
            label1.Text = result.ToString();
        }

        private static void SumData(object state)
        {
            int result;
            //int[] icount = (int[])state;
            int icount = (int)state;

            for (int i = icount; i > 0; i--)
            {
                result += i;
                System.Threading.Thread.Sleep(1000);
            }
            setTextboxText(result);
        }

        delegate void IntDelegate(int result);

        private void button2_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }
}

Why is this error occurring?

An object reference is required for the nonstatic field, method, or property 'WindowsApplication1.Form1.setTextboxText(int)

TylerH · Accepted Answer · 2025-04-01 00:56:21Z

It looks like you are calling a non static member (a property or method, specifically setTextboxText) from a static method (specifically SumData). You will need to either:

If you can, make setTextboxText static:
static void setTextboxText(int result)

HOWEVER, in this case, setTextboxText REQUIRES access to instance variables, so cannot be static.
Instead do:

Call setTextboxText via a static singleton of Form1:

class Form1
{
    public static Form1 It;   // Singleton.

    public Form1()
    {
        It = this;
    }

    private static void SumData(object state)
    {
        ...
        It.setTextboxText(result);
    }
}

Create an instance of Form1 within the calling method:

private static void SumData(object state)
{
    int result = 0;
    //int[] icount = (int[])state;
    int icount = (int)state;

    for (int i = icount; i > 0; i--)
    {
        result += i;
        System.Threading.Thread.Sleep(1000);
    }
    Form1 frm1 = new Form1();
    frm1.setTextboxText(result);
}

BUT that won't do what you want, if an instance of Form1 already exists.
Passing in an instance of Form1 would be an option also.

Make the calling method a non-static instance method (of Form1):

 private void SumData(object state)
 {
     int result = 0;
     //int[] icount = (int[])state;
     int icount = (int)state;

     for (int i = icount; i > 0; i--)
     {
         result += i;
         System.Threading.Thread.Sleep(1000);
     }
     setTextboxText(result);
 }

More info about this error can be found on MSDN.

Simon Nitzsche · Accepted Answer · 2017-10-15 17:48:32Z

25

For this case, where you want to get a Control of a Form and are receiving this error, then I have a little bypass for you.

Go to your Program.cs and change

Application.Run(new Form1());

to

public static Form1 form1 = new Form1(); // Place this var out of the constructor
Application.Run(form1);

Now you can access a control with

Program.form1.<Your control>

Also: Don't forget to set your Control-Access-Level to Public.

And yes I know, this answer does not fit to the question caller, but it fits to googlers who have this specific issue with controls.

edited Oct 15, 2017 at 17:48

answered Jan 7, 2017 at 20:28

Simon Nitzsche

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Comments

Brian Rasmussen · Accepted Answer · 2009-01-31 08:40:21Z

22

You start a thread which runs the static method SumData. However, SumData calls SetTextboxText which isn't static. Thus you need an instance of your form to call SetTextboxText.

answered Jan 31, 2009 at 8:40

Brian Rasmussen

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2 Comments

Robert Over a year ago

This answer appears to restate the problem. It doesn't explain why this produces an error.

Shidouuu Over a year ago

@Robert Neither do all the other answers... this comment was pointless

PiotrWolkowski · Accepted Answer · 2014-07-01 13:38:55Z

9

Your method must be static

static void setTextboxText(int result)
{
    if (this.InvokeRequired)
    {
        this.Invoke(new IntDelegate(SetTextboxTextSafe), new object[] { result }); 
    }
    else
    {
        SetTextboxTextSafe(result);
    }
}

edited Jul 1, 2014 at 13:38

PiotrWolkowski

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answered Jul 1, 2014 at 13:16

issam chouchane

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1 Comment

dbc Over a year ago

This specific method explicitly accesses instance properties (specifically this.InvokeRequired and this.Invoke) and so cannot be made static.

veggiebenz · Accepted Answer · 2018-07-27 02:34:38Z

5

Credit to @COOLGAMETUBE for tipping me off to what ended up working for me. His idea was good but I had a problem when Application.SetCompatibleTextRenderingDefault was called after the form was already created. So with a little change, this is working for me:


static class Program
{
    public static Form1 form1; // = new Form1(); // Place this var out of the constructor

    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(form1 = new Form1());
    }
}

answered Jul 27, 2018 at 2:34

veggiebenz

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Comments

Dean P · Accepted Answer · 2021-05-02 00:05:34Z

5

The essence, and solution, to your problem is this:

using System;

namespace myNameSpace
{
    class Program
    {
        private void method()
        {
            Console.WriteLine("Hello World!");
        }

        static void Main(string[] args)
        {
            method();//<-- Compile Time error because an instantiation of the Program class doesnt exist
            Program p = new Program();
            p.method();//Now it works. (You could also make method() static to get it to work)
        }
    }
}

answered May 2, 2021 at 0:05

Dean P

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Comments

Max Alexander Hanna · Accepted Answer · 2019-06-03 15:17:12Z

4

I actually got this error because I was checking InnerHtml for some content that was generated dynamically - i.e. a control that is runat=server.

To solve this I had to remove the "static" keyword on my method, and it ran fine.

answered Jun 3, 2019 at 15:17

Max Alexander Hanna

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Comments

Peter Mortensen · Accepted Answer · 2017-10-15 17:38:25Z

3

From my looking you give a null value to a textbox and return in a ToString() as it is a static method. You can replace it with Convert.ToString() that can enable null value.

edited Oct 15, 2017 at 17:38

Peter Mortensen

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answered Jan 12, 2013 at 12:20

Abd Al-Kareem Attiya

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