[ValueConversion(typeof(DateTime), typeof(string))]
    class DateTimeConverter1 : Freezable, IValueConverter
    {
        // Convertは問題なし。
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            // DateTime型 -> HH:ss (時刻だけを表示する)
            var d = System.Convert.ToDateTime(value);
            return d.ToString("HH:ss");
        }
 
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            // valueにはテキストボックスに入力したstring型の時刻(HH:mm)が入っている。
 
            DateTime time = System.Convert.ToDateTime(value.ToString());
            DateTime date = Date; // HogeDateの値
 
            // return ～
        }
 
 
        public DateTime Date
        {
            get { return (DateTime)GetValue(DayProperty); }
            set { SetValue(DayProperty, value); }
        }
        public static readonly DependencyProperty DayProperty =
            DependencyProperty.Register("Date", typeof(DateTime), typeof(DateTimeConverter1));
 
        protected override Freezable CreateInstanceCore()
        {
            return new DateTimeConverter1();
        }
    }
 
 
    <Window.Resources>
        <v:DateTimeConverter1 x:Key="converter1" Date="{Binding HogeDate}" />
    </Window.Resources>
 
    <TextBox Text="{Binding HogeDate,Converter={StaticResource converter1}}"/>
 

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