Restrict column in listview from being greater than X (NotifyPropertyChanged not working)

Question

Here is how my program behaves as I type numbers:

I have a listview that is binded to an observable collection. Here is my code: ( you may skeep this part the classes are very simple)

Class Item:

/// <summary>
/// Represent each row in listview
/// </summary>
public class Item : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }

    void UpdateSum()
    {
        Sum = Col1;// + col2 + col3 etc
    }

    decimal _Col1;
    public decimal Col1 //                                         ||
    {                   //                                         ||
        get             //                                         ||
        {               //                                         ||              
            return _Col1; //                                       ||                              
        }                 //                                       ||              
        set               //                                       ||                
        {                 //                                    \  ||   /                        
            if (value > 100)  //                                 \ || /                                
            {                 //                                   \/                  
                Col1 = 100;  // !!!!!!!!!!!!!!!!!!!!!  HERE why does the listview does't update!!!!!!!!
                NotifyPropertyChanged("Col1");
            }else
            {
                _Col1 = value;
            }
            UpdateSum();
            NotifyPropertyChanged("Col1");
        }
    }

    decimal _Sum;
    public decimal Sum
    {
        get
        {
            return _Sum;
        }
        set
        {
            _Sum = value;

            NotifyPropertyChanged("Sum");
        }
    }
}

Code Behind

using System;
using System.Windows;
using System.ComponentModel;
using System.Collections.ObjectModel;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {

        public ObservableCollection<Item> Collection = new ObservableCollection<Item>();

        public MainWindow()
        {
            InitializeComponent();

            this.Loaded += new RoutedEventHandler(MainWindow_Loaded);
        }

        void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {

            Collection.Add(new Item());
            listView2.DataContext = Collection;
            listView2.ItemsSource = Collection;
            listView2.IsSynchronizedWithCurrentItem = true;
        }
    }
}

Listview in xaml:

 <ListView Name="listView2" >
        <ListView.View>
            <GridView>
                <GridViewColumn Header="Column1" Width="200">
                    <GridViewColumn.CellTemplate>
                        <DataTemplate>
                            <TextBox Width="200" Text="{Binding Col1, UpdateSourceTrigger=PropertyChanged}"></TextBox>
                        </DataTemplate>
                    </GridViewColumn.CellTemplate>
                </GridViewColumn>
                <GridViewColumn Header="Sum" Width="200">
                    <GridViewColumn.CellTemplate>
                        <DataTemplate>
                            <TextBox Width="200" Text="{Binding Sum, UpdateSourceTrigger=PropertyChanged}"></TextBox>
                        </DataTemplate>
                    </GridViewColumn.CellTemplate>
                </GridViewColumn>

            </GridView>
        </ListView.View>
    </ListView>

---

Anyways why when I update Col1=100 it does not update in the listview! Also note how the sum comes to be 100 and not 1000.

I don't want column1 to be greater than some number x. In my real program that number changes dynamically and I calculate it inside the Item class.

How can I fix this?

---

---

Edit

I found something interesting... If I start typing different numbers taks a look at what happens: I will just type 5 in this example:

It works in step 3!!!

once it is equal to 100 it stops working...

Answer 1

I made it work!!! I changed:

 Text="{Binding Col1, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"

for:

 Text="{Binding Col1, Mode=TwoWay}"

But I need to update the property when the textbox changes so this migh be a solution for someone else...