Multibinding and IMultiValueConverter in WPF

Introduction

In some cases we might have several fields in your data model that represent a name (first name, middle name and last name) that you want to combine into a single entry in a list. Multibinding takes multiple values and combines them into another value. There are two ways to do multibinding, either using StringFormat or by a converter. The StringFormat is simple compared to a converter, so we will start with that first.

<TextBlock>
   <TextBlock.Text>
   <MultiBinding StringFormat=" {0}, {1}, {2}">
   <Binding ElementName="ThisWindow" Path="FirstName"/>
   <Binding ElementName="ThisWindow" Path="MiddleName"/>
   <Binding ElementName="ThisWindow" Path="LastName"/>
   </MultiBinding>
   </TextBlock.Text>
</TextBlock>

Here the {0} ,{1}, {2} values will be replaced at runtime with FirstName, MiddleName, LastName.

Using Converter

The converter must be derived from IMultiValueConverter and is very similar to a converter derived from IValueConverter, except that instead of having a single value as an argument, it takes multiple arguments.

public class TotalConverter : IMultiValueConverter
    {

        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            decimal Amount = 0;
            decimal Discount = 0;
            string TotalAmount = string.Empty;
            Amount = (values[0] != null && values[0] != DependencyProperty.UnsetValue) ? System.Convert.ToDecimal(values[0]) : 0;
            Discount = (values[0] != null && values[1] != DependencyProperty.UnsetValue) ? System.Convert.ToDecimal(values[1]) : 0;
            TotalAmount = System.Convert.ToString(Amount - Discount);
          return TotalAmount;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

Here in the value field we will get multiple values (amount and discount), after conversation the single value will be returned.

Now we have a MultiValue converter, we need to create an instance of it in a XAML resource.



We put in the main Window tag to remind you to put in the converter namespace. Then we instantiate the converter as a resource with a name. Now we can do our multibinding.

<TextBox Margin="2" MinWidth="120" Grid.Row="1" Grid.Column="1">
            <TextBox.Text>
                <MultiBinding Converter="{StaticResource Totalconverter }">
                    <Binding Path="Amount"   ElementName="ThisWindow"/>
                    <Binding Path="Discount"  ElementName="ThisWindow"/>
                </MultiBinding>
            </TextBox.Text>
        </TextBox>

Here we have the two properties (Amount and Discount), these properties are bound to the TextBox and implemented TotalConverter.

In MainWindow.xaml.cs:

public partial class MainWindow : Window, INotifyPropertyChanged
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        private decimal amount ;

        public decimal Amount
        {
            get { return amount; }
            set { amount = value;
            OnPropertyChanged("Amount");
            }
        }
        private decimal discount;

        public decimal Discount
        {
            get { return discount; }
            set { discount = value;
            OnPropertyChanged("Discount");
            }
        }


        #region INotifyPropertyChanged Members implementation

        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged(string txt)
        {

            PropertyChangedEventHandler handle = PropertyChanged;
            if (handle != null)
            {
                handle(this, new PropertyChangedEventArgs(txt));
            }
        }
        #endregion
    }

That's it. We made the application. Let me run the application.



Figure: Initial state



Figure: Amount = 2 and Discount = 0. So Amount – Discount = Total = 2



Figure: Amount = 223413 and Discount = 0. So Amount – Discount = Total = 223413



Figure: Amount = 223413 and Discount = 564554544. So Amount – Discount = Total = -564331131