On Screen Keypad in application C#

I am trying to Create KEYPAD for my application for a touch screen computer, I can't use windows onscreen keyboard. in my application in Form I have my KEYPAD GROUPBOX and I have multiple textbox's and one datagridview.

I did try to use SendKeys.Send() by this code

for code :

    public partial class Form1 : Form
  {
    const int W_ACTIVATE = 0x08000000;

    public Form1()
    {      
      InitializeComponent();      
    }

    protected override CreateParams CreateParams
    {
      get
      {
        CreateParams param = base.CreateParams;
        param.ExStyle |= W_ACTIVATE;
        return param;
      }
    }

    private void button1_Click(object sender, EventArgs e)
    {
     Button btn = (Button)sender;
        string btnTag = btn.Tag.ToString();
        switch (btnTag)
        {
            case "0":
                SendKeys.Send("(0)");

                break;
            case "1":
                SendKeys.Send("(1)");
                break;
            case "2":
                SendKeys.Send("(2)");
                break;
            case "3":
                SendKeys.Send("(3)");
                break;
            case "4":
                SendKeys.Send("(4)");
                break;
            case "5":
                SendKeys.Send("(5)");
                break;
            case "6":
                SendKeys.Send("(6)");
                break;
            case "7":
                SendKeys.Send("(7)");
                break;
            case "8":
                SendKeys.Send("(8)");
                break;
            case "9":
                SendKeys.Send("(9)");
                break;

            default:
                // Do Something
                break;
        }
    }
  }

But it doesn't work,I need Help ,I would like to know how to make the keys type into the textbox and active cell in Datagridview which is focused.