Q:

WIndows 10 UWP - How can I determine if a Key press is a letter or number?

Windows 10 UWP: Example: On UWP grid, a button1.content = 1 and a textbox. Using mouse to press button1.content, 1 is shown in the textbox.text.
How to simulate numeric keypad (1) and 1 is shown in the textbox.text?

A:

You can use TextBlock.Text to set the text to TextBlock.
If you want to know the key press, you should add KeyDown in Grid
<Grid KeyDown="Grid_OnKeyDown"></Grid>

And add the following code
private void Grid_OnKeyDown(object sender, KeyEventArgs e)
{
    var str = e.Key.ToString();
    if (char.IsDigit(str[0]))
    {
        //is digit
    }
    // is letter
}

You can use TextBlock.Text = xx to set the TextBlock.

