Hi If you use
SendKeys
function instead of appending a text from the soft keyboard then the autocomplte will be trigger.
private void button1_Click(object sender, EventArgs e)
{
textBox1.Focus();
SendKeys.Send("{A}");
}
Autocomplete mode work by hooking the current key state and the previous text in the textbox. So if you emulate the key state it supposed to work. I am not sure how you can do this with the touch screen.