CS 0120：非靜態字段、方法或屬性“foo”需要對象引用考慮：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();         }     }}為什么會發生此錯誤？非靜態字段、方法或屬性‘WindowsApplication1.Form1.setTextboxText(int)需要對象引用。