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

huda_60930 0
Viewed 1469803

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)

c#
9 Answers

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:

  1. Make the called member static also:

    static void setTextboxText(int result)
{
    // Write static logic for setTextboxText.  
    // This may require a static singleton instance of Form1.
}

  2. 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);
}

    Passing in an instance of Form1 would be an option also.

  3. 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.

Admin1

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.

user_382060

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());
    }
}
user_8920700

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.

user_63270860

Make the function static. This must solve your problem.

user_110673030

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)
        }
    }
}
user_59593720
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