Why does TextBox Border Colour insist on and not changing in WPF?

Question

As far as I understand I should be using Style triggers to update the TextBox\'s border colour when it is focused. However no matter what I do it always turns to the system

Answer 1

Try set for BorderThickness value more than 1 (by default):

Tested on Windows Seven.

Edit: why is this happening?

I looked in the default style for TextBox in Blend under Windows 7, here it is ControlTemplate:

Here there is two parameters:

RenderMouseOver="{TemplateBinding IsMouseOver}"
RenderFocused="{TemplateBinding IsKeyboardFocusWithin}"

They are responsible for blue gradient Border when states Focus and MouseOver and probably there stands a condition on BorderThickness and BorderBrush. If they remove / reset the blue gradient Border will disappear and will not need to set values for BorderThickness greater than 1.

In ILSpy I found ChangeVisualState(bool) method in TextBoxBase class, here it is:

internal override void ChangeVisualState(bool useTransitions)
{
    if (!base.IsEnabled)
    {
        VisualStateManager.GoToState(this, "Disabled", useTransitions);
    }
    else
    {
        if (this.IsReadOnly)
        {
            VisualStateManager.GoToState(this, "ReadOnly", useTransitions);
        }
        else
        {
            if (base.IsMouseOver)
            {
                VisualStateManager.GoToState(this, "MouseOver", useTransitions);
            }
            else
            {
                VisualStateManager.GoToState(this, "Normal", useTransitions);
            }
        }
    }

    if (base.IsKeyboardFocused)
    {
        VisualStateManager.GoToState(this, "Focused", useTransitions);
    }
    else
    {
        VisualStateManager.GoToState(this, "Unfocused", useTransitions);
    }

    base.ChangeVisualState(useTransitions);
}

It turns out that these visual states implemented "systematically" and in Styles not present.