HelpAuto key press doesn't work in game

I made this code, it's really simple and what it does is it presses or types whatever you put into the textbox. But this doesn't work in games. How do i make it work? The program doesn't focus onto the game

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Timer1.Start()
End Sub

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Timer1.Stop()
End Sub

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
SendKeys.Send(TextBox1.Text)
End Sub
End Class

Try other methods of sending the keys to the game:
- PostMessage / SendMessage
- SendInput
- keybd_event
- Hook DirectInput and inject directly into the buff (if the game uses it).
- Hook the games input system itself and inject directly into it.

Otherwise force the game into focus before you start using SendKeys and see if it helps.