How do you programtically underline text in a normal textbox

How would i, in runtime, set a textbox's underline font property to true? I tried:

Code:

---

txt.Font.Underline = True

---

but this property seems to be readonly for some reason.

Font objects are immutable, i.e. once you create one you cannot change it. If you want to change a font you have to create a new one and assign it to the relevant property. Because changing a font style is a common operation there is a constructor provided just for the occasion:

vb Code:

'Apply the underline style.
Me.TextBox1.Font = New Font(Me.TextBox1.Font, _
                            Me.TextBox1.Font.Style Or FontStyle.Underline)
 
'Remove the underline style.
Me.TextBox1.Font = New Font(Me.TextBox1.Font, _
                            Me.TextBox1.Font.Style And Not FontStyle.Underline)
 
'Toggle the underline style.
Me.TextBox1.Font = New Font(Me.TextBox1.Font, _
                            Me.TextBox1.Font.Style Xor FontStyle.Underline)

Note that after the first expression the text will be underlined no matter what it was before, after the second it will not be underlined no matter what it was before, while after the third it will be the opposite of what it was before.

Note also that this code affects the Underline style without affecting any other styles. That's why you use the existing Style property of the font.