An object reference is required for the non-static field

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

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.


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.


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.


Your method must be static

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

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