WPF UserControl的ValidationRule触发了， 但是这个TextBox的默认的ErrorTemplate没有看到红框
我创建了一个UserControl工程，里面有个TextBox，绑定了一个ValidationRule， 然后我在另一个wpf窗体程序中插入了这个UserControl，调试发现Textbox的ValidationRule触发了，但是默认的红框没有出现。

如果我把UserControl基类改为Window， 单独ShowDialog， 红框是有的。

相关代码：

XML code

<UserControl    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"    mc:Ignorable="d"    x:Class="UserControlValidationDemo.UserControl1"    xmlns:UserControlValidationDemo_ValidationRules="clr-namespace:UserControlValidationDemo.ValidationRules"    xmlns:UserControlValidationDemo_ViewModels="clr-namespace:UserControlValidationDemo.ViewModels"    x:Name="UserControl"    d:DesignWidth="640" d:DesignHeight="480">    <UserControl.Resources>        <UserControlValidationDemo_ViewModels:MainViewModel x:Key="MainViewModelDataSource" d:IsDataSource="True"/>    </UserControl.Resources>    <UserControl.DataContext>        <Binding Mode="OneWay" Source="{StaticResource MainViewModelDataSource}"/>    </UserControl.DataContext>        <Grid x:Name="LayoutRoot" Background="White">        <TextBox HorizontalAlignment="Left" TextWrapping="Wrap" VerticalAlignment="Top" x:Name="txtTest">            <TextBox.Text>                <Binding Path="Collection[0].Property1" UpdateSourceTrigger="PropertyChanged">                    <Binding.ValidationRules>                        <UserControlValidationDemo_ValidationRules:TestValidationRule />                    </Binding.ValidationRules>                </Binding>            </TextBox.Text>        </TextBox>    </Grid></UserControl>

namespace UserControlValidationDemo.ValidationRules
{
public class TestValidationRule : ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
if (GlobalDefinition.MainWnd is UserControl)
{
object t = Validation.GetErrorTemplate((GlobalDefinition.MainWnd as UserControl1).txtTest);
object e = Validation.GetErrors((GlobalDefinition.MainWnd as UserControl1).txtTest);

return new ValidationResult(false, "This is failed validation.");
}
else if (GlobalDefinition.MainWnd is Window)
{
object t = Validation.GetErrorTemplate((GlobalDefinition.MainWnd as Window1).txtTest);
object e = Validation.GetErrors((GlobalDefinition.MainWnd as Window1).txtTest);

return new ValidationResult(false, "This is failed validation.");
}

return new ValidationResult(false, "This is failed validation.");
}
}
}

C# code

[解决办法]
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[解决办法]
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