Question

I want to simulate data changing in the model and having that data be reflected in XAML. As I understand I need to implement INotifyPropertyChanged.

However, in the following code example, XAML displays the data from the customer only once but the date and time never changes.

What do I have to change in the following example to make XAML continually display the current date and time as it changes in the model?

In particular, I don’t understand how the Binding would know when to check the model, every second? 10 times a second? There is no event that it is responding to. What am I missing here?

XAML:

<Window x:Class="TestBinding99382.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TestBinding99382"
    Title="Window1" Height="300" Width="300">

    <Window.Resources>
        <ObjectDataProvider 
              x:Key="DataSourceCustomer" 
              ObjectType="{x:Type local:ShowCustomerViewModel}" 
              MethodName="GetCurrentCustomer"/>
    </Window.Resources>

    <DockPanel DataContext="{StaticResource DataSourceCustomer}">
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <TextBlock Text="{Binding Path=FirstName}"/>
            <TextBlock Text=" "/>
            <TextBlock Text="{Binding Path=LastName}"/>
        </StackPanel>
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
            <TextBlock Text="{Binding Path=TimeOfMostRecentActivity}"/>
        </StackPanel>

    </DockPanel>
</Window>

Code Behind:

using System.Windows;
using System.ComponentModel;
using System;

namespace TestBinding99382
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }
    }

    //view model
    public class ShowCustomerViewModel : INotifyPropertyChanged
    {
        private Customer _currentCustomer;

        public Customer CurrentCustomer
        {
            get
            {
                return _currentCustomer;
            }

            set
            {
                _currentCustomer = value;
                this.RaisePropertyChanged("CurrentCustomer");
            }
        }

        public ShowCustomerViewModel()
        {
            _currentCustomer = Customer.GetCurrentCustomer();
        }

        public Customer GetCurrentCustomer()
        {
            return _currentCustomer;
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string property)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(property));
            }
        }
    }

    //model
    public class Customer : INotifyPropertyChanged
    {
        private string _firstName;
        private string _lastName;
        private DateTime _timeOfMostRecentActivity;

        public string FirstName
        {
            get
            {
                return _firstName;
            }
            set
            {
                _firstName = value;
                this.RaisePropertyChanged("FirstName");
            }
        }

        public string LastName
        {

            get
            {
                return _lastName;
            }
            set
            {
                _lastName = value;
                this.RaisePropertyChanged("LastName");
            }
        }

        public DateTime TimeOfMostRecentActivity
        {

            get
            {
                return _timeOfMostRecentActivity;
            }
            set
            {
                _timeOfMostRecentActivity = value;
                this.RaisePropertyChanged("TimeOfMostRecentActivity");
            }
        }

        public static Customer GetCurrentCustomer()
        {
            return new Customer 
                     { FirstName = "Jim"
                       , LastName = "Smith"
                       , TimeOfMostRecentActivity = DateTime.Now};
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string property)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(property));
            }
        }
    }
}

Answer 1

Maybe I’m not getting what you wish this code to do.

You have created a Customer Object which implements INotifyPropertyChanged. You have another class which is a factory for the XAML to get to the instance.
Now you create a Customer instance with predefined properties. The View displays them. Unless you change the properties somehow, the View will not update.

I added a button to your WPF View

<Button DockPanel.Dock="Bottom" 
        x:Name="UpdateTime" 
        Click="UpdateTime_Click">
                 Update Activity Timestamp
 </Button>  

C# code-behind:

private void UpdateTime_Click(object sender, RoutedEventArgs e)
{
     Customer.GetCurrentCustomer().TimeOfMostRecentActivity = DateTime.Now;
}

I also changed Customer type to create a single instance for Current Customer

private static Customer _CurrentCustomer;

public static Customer GetCurrentCustomer()
{
    if (null == _CurrentCustomer)
    {
        _CurrentCustomer = new Customer 
        {   FirstName = "Jim"
           , LastName = "Smith"
           , TimeOfMostRecentActivity = DateTime.Now 
         };
    }
         return _CurrentCustomer;
}

Now each time I click the button, the DateTime Property is modified and the view auto-updates due to the INotifyPropertyChanged mechanism. The code seems to be working AFAISee.