转换器 IValueConverter

public class WidthConverter : IValueConverter{
public object Convert(object value, Type targetType, object parameter,  CultureInfo culture)
  {
            if (value != null)
            {
                double num = System.Convert.ToInt32(value);
                if (num != 0)
                {
                    return (double)(num - 40);
                }
                return 0d;
               }
            return null;
  }
 public object ConvertBack(object value, Type targetType, object parameter,  CultureInfo culture)
         {
            return null;
         }
 }

WidthConverter是对IValueConverter接口的两个方法的实现