DataTrigger的DataContext设置为窗口，这就是为什么它在窗口中查看状态的原因。您只需要告诉绑定状态在用户控件上即可。尝试以下操作：

The DataContext for the DataTrigger is set to the window, that's why it looks at the window for "State". You just need to tell the binding that State is on the user control. Try this:

<DataTrigger Binding="{Binding Path=State, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}}" Value="True">

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这是一个完整的示例：

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Here is a complete example:

MainWindow.xaml

MainWindow.xaml

<Window x:Class="WpfApplication89.MainWindow"
        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"
        xmlns:local="clr-namespace:WpfApplication89"
        mc:Ignorable="d"
        DataContext="{Binding RelativeSource={RelativeSource Self}}"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <local:UserControl1 State="{Binding Path=DualState}" />
        <CheckBox Content="DualState" IsChecked="{Binding DualState}" />
    </StackPanel>
</Window>

MainWindow.xaml.cs

MainWindow.xaml.cs

using System.Windows;

namespace WpfApplication89
{
    public partial class MainWindow : Window
    {
        public static readonly DependencyProperty DualStateProperty = DependencyProperty.Register("DualState", typeof(bool), typeof(MainWindow), new PropertyMetadata(false));

        public bool DualState
        {
            get { return (bool)GetValue(DualStateProperty); }
            set { SetValue(DualStateProperty, value); }
        }

        public MainWindow()
        {
            InitializeComponent();
        }
    }
}

UserControl1.xaml

UserControl1.xaml

<UserControl x:Class="WpfApplication89.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApplication89"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <TextBlock Text="User Control 1">
            <TextBlock.Style>
                <Style TargetType="TextBlock">
                    <Setter Property="Background" Value="Beige" />
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding Path=State, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}}" Value="true">
                            <Setter Property="Background" Value="Red" />
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </TextBlock.Style>
        </TextBlock>
    </Grid>
</UserControl>

UserControl1.xaml.cs

UserControl1.xaml.cs

using System.Windows;
using System.Windows.Controls;

namespace WpfApplication89
{
    public partial class UserControl1 : UserControl
    {
        public static readonly DependencyProperty StateProperty = DependencyProperty.Register("State", typeof(bool), typeof(UserControl1), new PropertyMetadata(false));

        public bool State
        {
            get { return (bool)GetValue(StateProperty); }
            set { SetValue(StateProperty, value); }
        }

        public UserControl1()
        {
            InitializeComponent();
        }
    }
}

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MainWindow.xaml.cs（INotifyPropertyChanged版本）

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MainWindow.xaml.cs (INotifyPropertyChanged version)

using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;

namespace WpfApplication89
{
    public partial class MainWindow : Window, INotifyPropertyChanged
    {

        #region INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        protected bool SetProperty<T>(ref T field, T value, [CallerMemberName]string name = null)
        {
            if (Equals(field, value))
            {
                return false;
            }
            field = value;
            this.OnPropertyChanged(name);
            return true;
        }
        protected void OnPropertyChanged([CallerMemberName]string name = null)
        {
            var handler = this.PropertyChanged;
            handler?.Invoke(this, new PropertyChangedEventArgs(name));
        }
        #endregion

        #region Property bool DualState
        private bool _DualState;
        public bool DualState { get { return _DualState; } set { SetProperty(ref _DualState, value); } }
        #endregion


        public MainWindow()
        {
            InitializeComponent();
        }
    }
}