MAUI中如何修改Windows平台Entry控件各视觉状态的边框样式？

1. 通过Handler修改各视觉状态的边框属性 #

WinUI的TextBox控件的视觉状态定义在其默认控件模板内部，直接调用GetVisualStateGroups()无法获取——这些状态属于模板内的元素而非TextBox本身。需要先获取模板中的Border控件（默认x:Name为BorderElement），再修改其视觉状态触发器的属性。

实现代码： #

在MauiProgram.cs中扩展EntryHandler的映射逻辑，借助Loaded事件确保控件模板加载完成后再操作：

builder.ConfigureMauiHandlers(handlers =>
{
#if WINDOWS
    handlers.AddHandler<Entry, EntryHandler>(handler =>
    {
        handler.PlatformView.Loaded += (s, e) =>
        {
            var textBox = handler.PlatformView;
            // 获取模板中的核心Border控件
            if (textBox.FindName("BorderElement") is Border borderElement)
            {
                var visualStateGroups = VisualStateManager.GetVisualStateGroups(borderElement);
                if (visualStateGroups == null) return;

                // 遍历并修改目标视觉状态的边框属性
                foreach (var group in visualStateGroups.OfType<VisualStateGroup>())
                {
                    foreach (var state in group.States.OfType<VisualState>())
                    {
                        switch (state.Name)
                        {
                            case "Normal":
                                state.Setters.Add(new Setter(Border.BorderThicknessProperty, new Thickness(1)));
                                state.Setters.Add(new Setter(Border.BorderBrushProperty, new SolidColorBrush(Colors.Gray)));
                                break;
                            case "PointerOver":
                                state.Setters.Add(new Setter(Border.BorderThicknessProperty, new Thickness(2)));
                                state.Setters.Add(new Setter(Border.BorderBrushProperty, new SolidColorBrush(Colors.Blue)));
                                break;
                            case "Focused":
                                state.Setters.Add(new Setter(Border.BorderThicknessProperty, new Thickness(2)));
                                state.Setters.Add(new Setter(Border.BorderBrushProperty, new SolidColorBrush(Colors.Green)));
                                break;
                        }
                    }
                }
            }
        };
    });
#endif
});

2. WinUI部分适配明暗主题的边框样式 #

之前修改Platforms/Windows/App.xaml资源字典仅支持单主题，是因为未将资源放入ThemeDictionaries对应的Light和Dark主题节点中。正确的做法是通过主题字典定义不同主题下的资源，再在视觉状态中引用，实现自动切换。

实现步骤： #

第一步：定义主题资源

在Platforms/Windows/App.xaml中添加分主题的资源字典：

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.ThemeDictionaries>
            <!-- Light主题资源 -->
            <ResourceDictionary x:Key="Light">
                <SolidColorBrush x:Key="EntryNormalBorderBrush" Color="Gray"/>
                <Thickness x:Key="EntryNormalBorderThickness">1</Thickness>
                <SolidColorBrush x:Key="EntryPointerOverBorderBrush" Color="Blue"/>
                <Thickness x:Key="EntryPointerOverBorderThickness">2</Thickness>
                <SolidColorBrush x:Key="EntryFocusedBorderBrush" Color="Green"/>
                <Thickness x:Key="EntryFocusedBorderThickness">2</Thickness>
            </ResourceDictionary>
            <!-- Dark主题资源 -->
            <ResourceDictionary x:Key="Dark">
                <SolidColorBrush x:Key="EntryNormalBorderBrush" Color="LightGray"/>
                <Thickness x:Key="EntryNormalBorderThickness">1</Thickness>
                <SolidColorBrush x:Key="EntryPointerOverBorderBrush" Color="LightBlue"/>
                <Thickness x:Key="EntryPointerOverBorderThickness">2</Thickness>
                <SolidColorBrush x:Key="EntryFocusedBorderBrush" Color="LightGreen"/>
                <Thickness x:Key="EntryFocusedBorderThickness">2</Thickness>
            </ResourceDictionary>
        </ResourceDictionary.ThemeDictionaries>
    </ResourceDictionary>
</Application.Resources>

第二步：引用主题资源（二选一）

• 方式一：结合Handler动态引用
  修改Handler中的Setters代码，替换为引用全局主题资源：

  // 以Normal状态为例，其他状态同理
  state.Setters.Add(new Setter(Border.BorderThicknessProperty, Application.Current.Resources["EntryNormalBorderThickness"]));
  state.Setters.Add(new Setter(Border.BorderBrushProperty, Application.Current.Resources["EntryNormalBorderBrush"]));
  

• 方式二：修改全局TextBox模板（全局生效）
  复制WinUI的TextBox默认模板到App.xaml，将视觉状态中的边框属性替换为主题资源引用（模板可从WinUI官方文档获取）：

  <Style TargetType="TextBox">
      <Setter Property="Template">
          <Setter.Value>
              <ControlTemplate TargetType="TextBox">
                  <!-- 省略其他模板元素 -->
                  <Border x:Name="BorderElement" CornerRadius="{TemplateBinding CornerRadius}">
                      <VisualStateManager.VisualStateGroups>
                          <VisualStateGroup x:Name="CommonStates">
                              <VisualState x:Name="Normal">
                                  <VisualState.Setters>
                                      <Setter Target="BorderElement.BorderThickness" Value="{StaticResource EntryNormalBorderThickness}"/>
                                      <Setter Target="BorderElement.BorderBrush" Value="{StaticResource EntryNormalBorderBrush}"/>
                                  </VisualState.Setters>
                              </VisualState>
                              <VisualState x:Name="PointerOver">
                                  <VisualState.Setters>
                                      <Setter Target="BorderElement.BorderThickness" Value="{StaticResource EntryPointerOverBorderThickness}"/>
                                      <Setter Target="BorderElement.BorderBrush" Value="{StaticResource EntryPointerOverBorderBrush}"/>
                                  </VisualState.Setters>
                              </VisualState>
                              <VisualState x:Name="Focused">
                                  <VisualState.Setters>
                                      <Setter Target="BorderElement.BorderThickness" Value="{StaticResource EntryFocusedBorderThickness}"/>
                                      <Setter Target="BorderElement.BorderBrush" Value="{StaticResource EntryFocusedBorderBrush}"/>
                                  </VisualState.Setters>
                              </VisualState>
                          </VisualStateGroup>
                      </VisualStateManager.VisualStateGroups>
                      <!-- 省略其他模板元素 -->
                  </Border>
              </ControlTemplate>
          </Setter.Value>
      </Setter>
  </Style>
  

切换系统明暗主题时，资源会自动同步，Entry的边框样式也会随之更新。

内容的提问来源于stack exchange，提问作者Barreto