如何僅在輸入有效時使用轉換器

Question

我有一個文本框用於輸入用於指定顏色的十六進制值。我有一個Validator驗證字符串是一個有效的十六進制顏色值。以及一個將「FF0000」字符串轉換爲「＃FFFF0000」.NET顏色對象的轉換器。我只想在數據有效時轉換值，就好像數據無效一樣，我會從轉換器中得到一個異常。我怎樣才能做到這一點？

代碼如下僅供參考

XAML

<TextBox x:Name="Background" Canvas.Left="328" Canvas.Top="33" Height="23" Width="60"> 
    <TextBox.Text> 
     <Binding Path="Background"> 
      <Binding.ValidationRules> 
       <validators:ColorValidator Property="Background" /> 
      </Binding.ValidationRules> 
      <Binding.Converter> 
       <converters:ColorConverter /> 
      </Binding.Converter> 
     </Binding> 
    </TextBox.Text> 
</TextBox> 

驗證

class ColorValidator : ValidationRule 
{ 
    public string Property { get; set; } 

    public ColorValidator() 
    { 
     Property = "Color"; 
    } 

    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo) 
    { 
     string entry = (string)value; 
     Regex regex = new Regex(@"[0-9a-fA-F]{6}"); 
     if (!regex.IsMatch(entry)) { 
      return new ValidationResult(false, string.Format("{0} should be a 6 character hexadecimal color value. Eg. FF0000 for red", Property)); 
     } 
     return new ValidationResult(true, ""); 
    } 
} 

轉換

class ColorConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 
    { 
     string entry = ((Color)value).ToString(); 
     return entry.Substring(3); 
    } 

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 
    { 
     string entry = (string)value; 
     return (Color)System.Windows.Media.ColorConverter.ConvertFromString("#FF" + entry); 
    } 
} 

Answer 1

您可以使用Binding.DoNothing或DependencyProperty.UnsetValue作爲轉換器中的返回值。

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 
{ 
    string entry = (string)value; 
    Regex regex = new Regex(@"[0-9a-fA-F]{6}"); 
    if (!regex.IsMatch(entry)) { 
     return Binding.DoNothing; 

    return entry.Substring(3); 
}