WPF用户控件数据绑定异常：运行时无法更新Slider属性

尝试创建一个包含Slider的用户控件，用于绑定Slider的Value、SelectionStart和SelectionEnd属性。编译阶段设置的值能正常显示，但点击按钮修改ViewModel属性时，用户控件的依赖属性未触发更新，Slider状态无法同步。

主窗口XAML #

xmlns:local="clr-namespace:DependencyPropertyExample"
    xmlns:uc="clr-namespace:DependencyPropertyExample.User_Controls"
    
    x:Name="MainWin"
    
    mc:Ignorable="d"
    Title="Slider Test"
    WindowStartupLocation="CenterScreen"
    Height="450"
    Width="200">

    <Grid >
    <Grid.RowDefinitions>
        <RowDefinition Height="40" />
        <RowDefinition Height="*" />
        <RowDefinition Height="40" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="100" />
        <ColumnDefinition Width="100" />
    </Grid.ColumnDefinitions>

    <Label Content="{Binding Path=Position, ElementName=userTest}" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" FontWeight="Bold" />
    <uc:UserTest x:Name="userTest" Position="{Binding Path=Pos}" Set_Title="THUMB" Set_SelStart="{Binding Path=Start}" Set_SelEnd="{Binding Path=End}" Grid.Row="1" Margin="0,0,0,20" />

    <Label Content="{Binding Value, ElementName=Slider1, StringFormat=\{0:D0\}}" Grid.Column="1" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" FontWeight="Bold" />
    <Slider x:Name="Slider1" Value="50" IsSelectionRangeEnabled="True" SelectionStart="10" SelectionEnd="90" Grid.Row="1" Grid.Column="1" Orientation="Vertical" HorizontalAlignment="Center" Maximum="100" SmallChange="1" Margin="0,45,0,24" />

    <Button x:Name="btn_Press" Content="Press" Grid.Row="2" Margin="10,10,10,10" Click="btn_Press_Click" />
</Grid>

主窗口后台代码 #

public static event PropertyChangedEventHandler PropertyChanged;

    public static void OnPropertyChanged([CallerMemberName] string? propertyname = null)
    {
        PropertyChanged?.Invoke(null, new PropertyChangedEventArgs(propertyname));
    }


    private double _start { get; set; }

    public double Start
    {
        get { return _start; }
        set 
        {
            _start = value;
            OnPropertyChanged("Start");
        }
    }

    private double _end { get; set; }

    public double End
    {
        get { return _end; }
        set
        {
            _end = value;
            OnPropertyChanged("End");
        }
    }

    private double _pos { get; set; }

    public double Pos
    {
        get { return _pos; }
        set
        {
            _pos = value;
            OnPropertyChanged("Pos");
        }
    }


    public MainWindow()
    {
        InitializeComponent();

        DataContext = this;

        Start = 10;
        End = 90;
        Pos = 50;
    }

    private void btn_Press_Click(object sender, RoutedEventArgs e)
    {
        Start = 30;
        End = 60;
        Pos = 70;
    }
}

UserTest用户控件XAML #

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="40" />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>

    <Label x:Name="title" Content="{Binding Set_Title, ElementName=SliderRoot}" Grid.Row="0" Grid.Column="0" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" FontWeight="Bold" />

    <Slider x:Name="Digit_Slider" 
            Orientation="Vertical"
            Value="{Binding Position, RelativeSource={RelativeSource AncestorType=UserControl}}"
            SelectionStart="{Binding Set_SelStart, RelativeSource={RelativeSource AncestorType=UserControl}}"
            SelectionEnd="{Binding Set_SelEnd, RelativeSource={RelativeSource AncestorType=UserControl}}"
            Grid.Row="1"
            Grid.Column="0" 
            HorizontalContentAlignment="Center" 
            VerticalContentAlignment="Center" 
            Margin="0,5,0,5" 
            Maximum="100" 
            HorizontalAlignment="Center" 
            IsSelectionRangeEnabled="True" 
            RenderTransformOrigin="0.5,0.5" 
            IsDirectionReversed="True" 
            Cursor="Hand"
            ValueChanged="Digit_Slider_ValueChanged" />
</Grid>

UserTest用户控件后台代码 #

public static readonly DependencyProperty Title_Property =
        DependencyProperty.Register("Set_Title", typeof(string), typeof(UserTest), new PropertyMetadata(string.Empty));

    public static DependencyProperty SelStart_Property =
        DependencyProperty.Register("Set_SelStart", typeof(double), typeof(UserTest), new PropertyMetadata(0.0, OnSelStart_Changed));

    public static readonly DependencyProperty SelEnd_Property =
        DependencyProperty.Register("Set_SelEnd", typeof(double), typeof(UserTest), new PropertyMetadata(0.0, OnSelEnd_Changed));

    public static DependencyProperty Pos_Property =
        DependencyProperty.Register("Position", typeof(double), typeof(UserTest), new PropertyMetadata(0.0, OnPosition_Changed));

    private static void OnSelStart_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var User = d as UserTest;
        User.Digit_Slider.SelectionStart = (double)e.NewValue;
    }

    private static void OnSelEnd_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var User = d as UserTest;
        User.Digit_Slider.SelectionEnd = (double)e.NewValue;
    }

    private static void OnPosition_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var User = d as UserTest;
        User.Digit_Slider.Value = (double)e.NewValue;
    }

    // Set TITLE (string) property of Slider
    public string Set_Title
    {
        get { return (string)GetValue(Title_Property); }
        set { SetValue(Title_Property, value); }
    }

    // Set SELECTION START (double) property of Slider
    // MODE = 1 Way (Write)
    public double Set_SelStart
    {
        get { return (double)GetValue(SelStart_Property); }
        set { SetValue(SelStart_Property, value); }
    }

    // Get VALUE (double) property of Slider
    // MODE = 2 Way (Read / Write)
    public double Position
    {
        get { return (double)GetValue(Pos_Property); }
        set { 
            SetValue(Pos_Property, value); 
        }
    }

    // Set SELECTION END (double) property of Slider
    public double Set_SelEnd
    {
        get { return (double)GetValue(SelEnd_Property); }
        set { SetValue(SelEnd_Property, value); }
    }

    #endregion DEPENDENCY_PROPERTIES

    public UserTest()
    {
        InitializeComponent();
    }

解决方案 #

问题出在主窗口的PropertyChanged事件定义为静态，WPF的数据绑定系统无法正确订阅静态事件来更新UI绑定。将事件和触发方法改为非静态即可：

修改主窗口的事件和方法：

// 去掉static修饰符
public event PropertyChangedEventHandler PropertyChanged;

// 去掉static修饰符
public void OnPropertyChanged([CallerMemberName] string? propertyname = null)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
}

补充说明： #

1. WPF绑定系统默认监听的是实例级的INotifyPropertyChanged事件，静态事件无法被绑定引擎正确处理，导致属性更新时无法通知到绑定目标（用户控件的依赖属性）。
2. 用户控件中通过依赖属性回调直接设置Slider属性的逻辑是正常的，只要依赖属性能接收到绑定源的更新值，就能同步到Slider上。

内容的提问来源于stack exchange，提问作者user3119168