C # static function, how to operate the controls in the Form?

1.第一个问题，关于，回调函数是否必须为静态函数或者全局函数？

2.第二个问题，静态函数，如何操作Form中的控件？

public static Form1 form1;

public Form1()
{
   InitializeComponent();

   form1 = this;
}

state.workSocket = handler;
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallback), state);

public static void ReadCallback(IAsyncResult ar)
{
 Form1.form1.textBoxReceive.AppendText(strmsgtemp);
}

3. The third question: the non-threaded create a control, not access

//非创建控件线程，无法访问
//richTextBox1.AppendText(Encoding.ASCII.GetString(data, 0, recvlength));

delegate void richtexttip();
richtexttip richtext3 = delegate()
{
  richTextBox1.AppendText("client:"+Encoding.Unicode.GetString(data, 0, recvlength) + "\r\n");
};
richTextBox1.Invoke(richtext3);