#927 – Limiting the Size of a TextBox

By default, a TextBox is high enough to accommodate a single line of text and wide enough to accommodate it’s widest line.  The TextBox sizes to fits its content, even if the content changes at run-time.

For example, if we don’t constrain the size of a TextBox and then add and remove lines at run-time, its content will change:

        private void btnAdd_Click(object sender, RoutedEventArgs e)
        {
            MyText = MyText + Environment.NewLine +
                string.Format("This is line {0}", nextLine++);
        }

We can, however, constrain the height by setting the MinLines and MaxLines property of the TextBox.

        <TextBox Text="{Binding MyText}"
                 TextWrapping="NoWrap"
                 HorizontalAlignment="Center"
                 Margin="5"
                 MaxLines="2"/>

In the example above, when we continue adding lines, the TextBox still only shows two lines.

If we enabled a vertical scrollbar, we’d see that we actually have three lines (after adding three) and we could scroll down to the third line.