WPF 使用MultiBinding ，TwoWay ，ValidationRule ，需要注意的事项

当wpf使用multibinding时， 其内部的validaterule的value 是其多个Binding的值， 要根据情况去验证， 还有就是在做IMultiConverter的ConvertBack时注意TargetType

如： 以下是一个Textbox通过MultiBinding绑定到后台 的字段， 以及前台的一个radiobutton, 该textbox有个validaterule。 

 <TextBox x:Name="txtPatientWeight" TextWrapping="Wrap" Margin="3" MaxLength="5" TabIndex="6" BorderBrush="Black" Grid.Row="5" Grid.Column="1" Height="22" MinWidth="42" Tag="PatientWeight"

                     Visibility="{Binding DataContext, ElementName=window, Converter={StaticResource KeyToVisibilityConverter}, ConverterParameter=PatientWeight}">

                <MultiBinding  Mode="TwoWay" Converter="{StaticResource WeightConverter}"   UpdateSourceTrigger="PropertyChanged">

                    <MultiBinding.ValidationRules>

                        <McsfPAFEContainee_ValidationRules:WeightValidationRule ValidatesOnTargetUpdated="True" ValidationStep="ConvertedProposedValue"/>

                    </MultiBinding.ValidationRules>

                    <Binding Path="PatientWeight"/>

                    <Binding Path="IsChecked" ElementName="rdoKg"/>

                </MultiBinding>

                <i:Interaction.Behaviors>

                    <McsfPAFEContainee_Behaviors:NumericTextBoxBehavior MinValue="0" MaxValue="300" />

                </i:Interaction.Behaviors>

            </TextBox>

////////////////////////

 <RadioButton x:Name="rdoKg" Content="kg" GroupName="WeightMeasure" d:LayoutOverrides="GridBox" MinWidth="34" Margin="5,0,0,0" Tag="PatientWeight" HorizontalAlignment="Center">

                    <RadioButton.IsChecked>

                        <Binding Path="DataContext" Mode="TwoWay" ElementName="window" Converter="{StaticResource DefaultUnitConverter}" ConverterParameter="kg"  UpdateSourceTrigger="PropertyChanged"></Binding>

                    </RadioButton.IsChecked>

                </RadioButton>

//////////////

  private string patientWeight = "";//(0010,1030) Patient Weight PatientWeight DS unit kg

        public string PatientWeight

        {

            get { return patientWeight; }

            set

            {

                if (value == patientWeight)

                {

                    return;

                }

                patientWeight = value;

                OnPropertyChanged("PatientWeight");

            }

        }

  

//////////converter

 public class WeightConverter : IMultiValueConverter

    {

        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)

        {

            if (null == values || 2 != values.Length )

            {

                return "";

            }

            string unit = "";

            string temp = values[0].ToString();

            if (String.IsNullOrEmpty(temp))

            {

                return "";

            }

            if (0 <= temp.IndexOf("lb"))

            {

                unit = "lb";

            }

            else if (0 <= temp.IndexOf("kg"))

            {

                unit = "kg";

            }

            else

            {

                return "";

            }

            string number = "";

            number = temp.Substring(0, temp.IndexOf(unit));

            //KG

            if ((bool)values[1])

            {

                measurementUnit = "kg";

            }

            else //LB

            {

                measurementUnit = "lb";

            }

            return ConvertToTargetValue(number, unit, measurementUnit);

        }

        private string measurementUnit = "";

      

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)

        {

            string temp = value.ToString();

            if (String.IsNullOrEmpty(temp))

            {

                return new object[]{DependencyProperty.UnsetValue, DependencyProperty.UnsetValue};

            }

            if (String.IsNullOrEmpty(measurementUnit))

            {

                measurementUnit = (PAFEContainee.MainDataContext as MainViewModel).PRCfgVM.IsDefaultKilogram ? "kg" : "lb";

            }

            object[] list = new object[2];

            list[0] = value.ToString() + measurementUnit;

            list[1] = measurementUnit.Equals("kg") ? "true" : "false";

            return list;

        }

        private string ConvertToTargetValue(string before, string beforeUnit, string afterUnit)

        {

            string result = "";

            if (beforeUnit.Equals(afterUnit))

            {

                return before;

            }

            switch (afterUnit)

            {

                case "lb":

                    result = ConvertKgToPound(before).ToString();

                    break;

                case "kg":

                    result = ConvertPoundToKg(before).ToString();

                    break;

                default:

                    break;

            }

            return result;

        }

        private double ConvertPoundToKg(string pound)

        {

            double kg = 0.4536 * double.Parse(pound);

            return kg;

        }

        private double ConvertKgToPound(string kg)

        {

            double pound = 2.20 * double.Parse(kg);

            return pound;

        }

    }

///////ValidationRule

 public override ValidationResult DoValidate(object value, CultureInfo cultureInfo)

        {

            try

            {

                //string field = value.ToString().Trim();

                string field = (value as object[])[0].ToString();

                string pattern = @"^([1-9]|[1-9][0-9]|[1-5][0-9][0-9]|600)((kg)|(lb))$";

                Regex reg = new Regex(pattern, RegexOptions.IgnoreCase);

                if (field.Length <= 0 || false == reg.IsMatch(field))

                {

                    return new ValidationResult(false, "Please input a number, for example '60'");

                }

                else

                {

                    return ValidationResult.ValidResult;

                }

            }

            catch

            {

                return new ValidationResult(false, "Patient weight convert failed.");

            }

        }