依赖属性不会更新Silverlight 4

<local:Snapshot BrandID=\"{Binding Path=Session.Test}\" />

<TextBlock Text=\"Sample text\" x:Name=\"brandIDTBlock\" />

public string BrandID
{
    get { return (string)GetValue(BrandIdProperty); }
    set { SetValue(BrandIdProperty, value); }
}

public static readonly DependencyProperty BrandIdProperty = DependencyProperty.Register(\"BrandID\", typeof(string), typeof(Snapshot), new PropertyMetadata(new PropertyChangedCallback(OnBrandIdChange)));

private static void OnBrandIdChange(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var control = (Snapshot)d;
    control.brandIDTBlock.Text = (string)e.NewValue;
}

private string _test = \"Test Value Binding\";

public string Test 
{
    get { return _test; }
    set { _test = value; } 
}

public string Test
{
    get { return _test; }
    set
    {
        _test = value;
        OnPropertyChanged(\"Test\");
    }
}

public event PropertyChangedEventHandler PropertyChanged;

protected void OnPropertyChanged(string name)
{
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null)
    {
        handler(this, new PropertyChangedEventArgs(name));
    }
}