为什么在WPF中坚持使用TextBox Border Color而不进行更改？

尝试设置BorderThickness大于1（默认）的值：

<Window.Resources>
    <Style TargetType="{x:Type TextBox}">
        <Style.Triggers>
            <Trigger Property="IsFocused" Value="True">
                <Setter Property="BorderBrush" Value="Pink" />
            </Trigger>
        </Style.Triggers>
    </Style>
</Window.Resources>

<Grid>
    <TextBox Width="100"
             Height="30"
             Text="Test" 
             BorderThickness="4" />
</Grid>

在Windows 7上进行了测试。

Edit: why is this happening?

我TextBox在Windows 7下的Blend中使用了默认样式，这里是ControlTemplate：

<ControlTemplate x:Key="TextBoxControlTemplate1" TargetType="{x:Type TextBox}">
    <Microsoft_Windows_Themes:ListBoxChrome x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderFocused="{TemplateBinding IsKeyboardFocusWithin}" SnapsToDevicePixels="true">
        <ScrollViewer x:Name="PART_ContentHost" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
    </Microsoft_Windows_Themes:ListBoxChrome>

    <ControlTemplate.Triggers>
        <Trigger Property="IsEnabled" Value="false">
            <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
        </Trigger>
    </ControlTemplate.Triggers>
</ControlTemplate>

这里有两个参数：

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

当状态为时，它们负责蓝色渐变边框Focus，MouseOver并且可能在BorderThickness和上存在条件BorderBrush。如果它们remove / reset是蓝色的，则“渐变边框”将消失，并且不需要将值设置为BorderThickness大于1。

在ILSpy我发现ChangeVisualState(bool)在TextBoxBase类的方法，那就是：

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);
}

事实证明，这些视觉状态是“系统地”实现的，并且没有样式。