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

gistfile1.cs

It looks like you are calling a non static property from a static method. You will need to either make the property static, or create an instance of class


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


or

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);
    }
    MyClass objMyClass = new MyClass();
    objMyClass.setTextboxText(result);
}