How to bind calculated value in c# method to TextBox?

Question

I want to calculate the sum of a column in my list(ObservableCollection displayed in ListView) and display it in TextBox.

<ListView x:Name="ProductListView" ItemsSource="{Binding ViewModel}">
<TextBlock Text="{Binding ???, StringFormat={}{0:N2}}" />

I have written a method in my ViewModel for this. But now I don't know how to bind the variable res to TextBox (The TextBox should always be updated when the ListView is changed).

public void CalcTotal()
{
    decimal res = 0;
    for (var i = 0; i < ProductsList.Count; i++)
    {
        res += ProductsList[i].Amount;
    }
}

Thanks!

Answer 1

Hi Imilio,
instead of method use property binding with your code in getter:

<ListView x:Name="ProductListView" ItemsSource="{Binding ViewModel}">
<TextBlock Text="{Binding CalcTotal, StringFormat={}{0:N2}}" />

...

 public decimal CalcTotal()
 get
   {
     decimal res = 0;
     for (var i = 0; i < ProductsList.Count; i++) res += ProductsList[i].Amount;
     return res;
  }
 }

Answer 2

Hi,
try following demo:

XAML:

<Window x:Class="WpfApp1.Window105"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp105"
        mc:Ignorable="d"
        Title="Imilio-3053_220214" Height="450" Width="800">
  <Window.DataContext>
    <local:ProductViewModel/>
  </Window.DataContext>
  <StackPanel>
    <Button Content="new Amount" Command="{Binding}"/>
    <ListView ItemsSource="{Binding View}">
      <ListView.View>
        <GridView>
        <GridViewColumn Header="Amount" Width="100" DisplayMemberBinding="{Binding Amount}"/>
      </GridView>
        </ListView.View>
    </ListView>
    <TextBlock Text="{Binding CalcTotal, StringFormat={}{0:N2}, Mode=OneWay}"/>
  </StackPanel>
</Window>

ViewModels:

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Data;
using System.Windows.Input;

namespace WpfApp105
{
  public class ProductViewModel : BaseViewModell, ICommand
  {
    public ProductViewModel() => cvs.Source = ProductsList;
    private CollectionViewSource cvs = new CollectionViewSource();
    private ObservableCollection<Data> ProductsList = new ObservableCollection<Data>();
    private Random rnd = new Random();

    public ICollectionView View { get => cvs.View; }

    public decimal CalcTotal
    {
      get
      {
        decimal res = 0;
        for (var i = 0; i < ProductsList.Count; i++)
        {
          res += ProductsList[i].Amount;
        }
        return res;
      }
    }

    public event EventHandler CanExecuteChanged;
    public void Execute(object parameter)
    {
      ProductsList.Add(new Data() { Amount = (decimal)(Math.Round(rnd.NextDouble() * 100,2))});
      RaisePropertyChanged(nameof(CalcTotal));
    }
    public bool CanExecute(object parameter) => true;
  }

  public class Data
  {
    public decimal Amount { get; set; } 
  }

  public class BaseViewModell : INotifyPropertyChanged
  {
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = "") =>
      this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));   
  }
}