UserControl上的DataContext更改不更新子控件的属性

Question

我有这个简单的控制：

<UserControl x:Class="MyProject.Controls.ImageToggleButton"
             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"
             d:DesignHeight="480"
             d:DesignWidth="480"
             Loaded="OnLoaded"
             Tap="OnTap"
             Background="{x:Null}">

    <Image x:Name='ButtonImage' />
</UserControl>

代码背后：

    public partial class ImageToggleButton
    {
        public static readonly DependencyProperty CheckedImageProperty = DependencyProperty.Register("CheckedImage", typeof(ImageSource), typeof(ImageToggleButton), new PropertyMetadata(default(ImageSource), OnPropertyChanged));

        public static readonly DependencyProperty IsCheckedProperty = DependencyProperty.Register("IsChecked", typeof(bool), typeof(ImageToggleButton), new PropertyMetadata(default(bool), OnPropertyChanged));

        public static readonly DependencyProperty UncheckedImageProperty = DependencyProperty.Register("UncheckedImage", typeof(ImageSource), typeof(ImageToggleButton), new PropertyMetadata(default(ImageSource), OnPropertyChanged));

        public ImageToggleButton()
        {
            this.InitializeComponent();
        }

        public ImageSource CheckedImage
        {
            get { return (ImageSource)this.GetValue(CheckedImageProperty); }
            set { this.SetValue(CheckedImageProperty, value); }
        }

        public bool IsChecked
        {
            get { return (bool)this.GetValue(IsCheckedProperty); }
            set { this.SetValue(IsCheckedProperty, value); }
        }

        public ImageSource UncheckedImage
        {
            get { return (ImageSource)this.GetValue(UncheckedImageProperty); }
            set { this.SetValue(UncheckedImageProperty, value); }
        }

        private static void OnPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((ImageToggleButton)d).UpdateImage();
        }

        private void OnLoaded(object sender, RoutedEventArgs e)
        {
            this.UpdateImage();
        }

        private void OnTap(object sender, GestureEventArgs e)
        {
            this.IsChecked = !this.IsChecked;
        }

        private void UpdateImage()
        {
            this.ButtonImage.Source = this.IsChecked ? this.CheckedImage : this.UncheckedImage;
        }
    }

此控件包含在另一个UserControl中，该DataTemplate用作LongListSelector.ItemTemplate的{​​{1}}。

(Some xaml snipped for brevity...)
<UserControl ...>
    <Grid>
        <controls:ImageToggleButton Grid.Column="0"
                                    CheckedImage="/Assets/icon_checked.png"
                                    UncheckedImage="/Assets/icon_unchecked.png"
                                    IsChecked="{Binding Store.IsSelected}"
                                    Height="48" />
    </Grid>
</UserControl>

DataContext是一个包含Store成员的视图模型，其中Store是类型为的对象：

public class Store : NotificationObject
{
    private bool isSelected;
    public bool IsSelected
    {
        get { return isSelected; }
        set { this.Set(() => IsSelected, ref IsSelected, value); }
    }
}

我的问题是，当LongListSelector为父控件设置新的DataContext时，IsChecked值无法在图像上正确更新。