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How to Resolve an object reference is required for the non-static field

How to Resolve an object reference is required for the non-static field
Table of Contents

The C# “an object reference is required for the non-static field” error is thrown when an object reference is required for the nonstatic field, method or property..

Install the C# SDK to identify and fix these errors

Introduction to an Object Reference is required for the non-static field

An object reference is required for the nonstatic field, method, or property 'member'

In order to use a non-static field, method, or property, you must first create an object instance.

Consider the following C# example


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 happening?

An object reference is required for the nonstatic
field, method, or property

'WindowsApplication1.Form1.setTextboxText(int)

Calling a non static member (a property or method, specifically setTextboxText) from a static method (specifically SumData) is causing this error.

How to fix: Object Reference is required for the non-static field?

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);
}

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References

[1] StackOverFlow, 2021. Online: https://stackoverflow.com/questions/498400/cs0120-an-object-reference-is-required-for-the-nonstatic-field-method-or-prop

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