在代码后置中创建Style Trigger，两个Setter仅一个生效

核心原因 #

你遇到的问题是WPF属性值优先级导致的：

• 直接在pdfButton实例上设置的Foreground = Brushes.Red属于「本地值」，优先级高于Style中Trigger里的Setter，因此Trigger的Foreground修改无法生效。
• 而BorderThickness没有设置本地值，所以Trigger的Setter能正常覆盖默认值。

解决方案一：将Foreground移到Style的默认Setter中 #

移除Button实例上的Foreground = Brushes.Red，转而在Style里添加默认的Foreground Setter，这样Trigger的Setter优先级更高，就能正常覆盖：

var foregroundSetter = new Setter()
{
    Property = Button.ForegroundProperty,
    Value = Brushes.LightGray
};

var borderThicknessSetter = new Setter()
{
    Property = Button.BorderThicknessProperty,
    Value = new Thickness(0)
};

var isEnabledTrigger = new Trigger()
{
    Property = Button.IsEnabledProperty,
    Value = false
};
isEnabledTrigger.Setters.Add(foregroundSetter);
isEnabledTrigger.Setters.Add(borderThicknessSetter);

var style = new Style(typeof(Button));
// 添加默认Foreground的Setter
style.Setters.Add(new Setter(Button.ForegroundProperty, Brushes.Red));
// 补充其他默认样式Setter
style.Setters.Add(new Setter(Button.BorderBrushProperty, Brushes.Transparent));
style.Setters.Add(new Setter(Button.BackgroundProperty, Brushes.Transparent));
style.Setters.Add(new Setter(Button.FontSizeProperty, 9.0));
style.Setters.Add(new Setter(Button.FontWeightProperty, FontWeights.SemiBold));
style.Setters.Add(new Setter(Button.PaddingProperty, new Thickness(0)));

style.Triggers.Add(isEnabledTrigger);

var pdfButton = new Button()
{
    Margin = new Thickness(0, 0, 5, 0),
    Height = 18,
    Width = 20,
    Content = "PDF",
    ToolTip = new ToolTip() { Content = "Create PDF of training day." },
    Command = CreatePdfCommand,
    CommandParameter = newTab,
    Style = style
};

解决方案二：自定义Button的ControlTemplate #

如果需要保留实例上的属性设置，可以自定义ControlTemplate，让内部TextBlock的Foreground直接绑定到Button的Foreground，确保Trigger的修改能传递到显示文本：

// 创建ControlTemplate
var buttonTemplate = new ControlTemplate(typeof(Button));

// 构建模板视觉树
var borderFactory = new FrameworkElementFactory(typeof(Border));
borderFactory.SetValue(Border.BorderBrushProperty, Brushes.Transparent);
borderFactory.SetValue(Border.BackgroundProperty, Brushes.Transparent);
borderFactory.SetValue(Border.BorderThicknessProperty, new Thickness(0));

var textBlockFactory = new FrameworkElementFactory(typeof(TextBlock));
// 绑定Text到Button的Content
textBlockFactory.SetBinding(TextBlock.TextProperty, new Binding("Content") { RelativeSource = RelativeSource.TemplatedParent });
// 绑定Foreground到Button的Foreground
textBlockFactory.SetBinding(TextBlock.ForegroundProperty, new Binding("Foreground") { RelativeSource = RelativeSource.TemplatedParent });
textBlockFactory.SetValue(TextBlock.FontSizeProperty, 9.0);
textBlockFactory.SetValue(TextBlock.FontWeightProperty, FontWeights.SemiBold);
textBlockFactory.SetValue(TextBlock.HorizontalAlignmentProperty, HorizontalAlignment.Center);
textBlockFactory.SetValue(TextBlock.VerticalAlignmentProperty, VerticalAlignment.Center);

borderFactory.AppendChild(textBlockFactory);
buttonTemplate.VisualTree = borderFactory;

// 构建Style
var foregroundSetter = new Setter()
{
    Property = Button.ForegroundProperty,
    Value = Brushes.LightGray
};

var borderThicknessSetter = new Setter()
{
    Property = Button.BorderThicknessProperty,
    Value = new Thickness(0)
};

var isEnabledTrigger = new Trigger()
{
    Property = Button.IsEnabledProperty,
    Value = false
};
isEnabledTrigger.Setters.Add(foregroundSetter);
isEnabledTrigger.Setters.Add(borderThicknessSetter);

var style = new Style(typeof(Button));
style.Setters.Add(new Setter(Button.TemplateProperty, buttonTemplate));
style.Triggers.Add(isEnabledTrigger);

var pdfButton = new Button()
{
    Padding = new Thickness(0, 0, 0, 0),
    Margin = new Thickness(0, 0, 5, 0),
    Height = 18,
    Width = 20,
    Content = "PDF",
    FontSize = 9,
    FontWeight = FontWeights.SemiBold,
    Foreground = Brushes.Red,
    BorderBrush = Brushes.Transparent,
    Background = Brushes.Transparent,
    ToolTip = new ToolTip() { Content = "Create PDF of training day." },
    Command = CreatePdfCommand,
    CommandParameter = newTab,
    Style = style
};

内容的提问来源于stack exchange，提问作者Steve S