Understanding MVVM Pattern

Question

I am trying to understand the MVVM pattern. I am following the tutorial here. I am stock at Example 4, framework. Putting the code cause issue for me at least for the observable class. I created a new folder called it HelperClass inside my project and copy and pasted the observable class.

Observable.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq.Expressions;

namespace Morza.HelperClass
{
    [Serializable]
    public abstract class ObservableObject : INotifyPropertyChanged
    {
        [field: NonSerialized]
        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
        {
            var handler = this.PropertyChanged;
            if (handler != null)
            {
                handler(this, e);
            }
        }

        protected void RaisePropertyChanged<T>(Expression<Func<T>> propertyExpresssion)
        {
            var propertyName = PropertySupport.ExtractPropertyName(propertyExpresssion);
            this.RaisePropertyChanged(propertyName);
        }

        protected void RaisePropertyChanged(String propertyName)
        {
            VerifyPropertyName(propertyName);
            OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
        }

        /// <summary>
        /// Warns the developer if this Object does not have a public property with
        /// the specified name. This method does not exist in a Release build.
        /// </summary>
        [Conditional("DEBUG")]
        [DebuggerStepThrough]
        public void VerifyPropertyName(String propertyName)
        {
            // verify that the property name matches a real,  
            // public, instance property on this Object.
            if (TypeDescriptor.GetProperties(this)[propertyName] == null)
            {
                Debug.Fail("Invalid property name: " + propertyName);
            }
        }
    }
}

However PropertySupport say it does not exist in the current concept. Morza is the project name.

My second questions:

If I want to implement observable, do I need to implement two ViewModel, where

If I have a person I would do the following

Model
  Person

ViewModel
  PersonViewModel
  PersonListViewModel

Where PersonListViewModel would have an observable list of PersonViewModel?

Answer 1

PropertySupport is not part of .NET. If you are using a framework tutorial, make sure to include that framework in your project.

The standard INotifyPropertyChanged implementation looks like this:

    public event PropertyChangedEventHandler PropertyChanged;

    // This method is called by the Set accessor of each property. 
    // The CallerMemberName attribute that is applied to the optional propertyName 
    // parameter causes the property name of the caller to be substituted as an argument. 
    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

From MSDN.

To answer your second question, your whole view should have a view model. That view model would then contain your list of Person objects. If you want to make separate Person model and view model objects, then it would contain a PersonViewModel collection instead. This separation is often unnecessary however.

PersonListViewModel is very unlikely to be needed. Just by the name, it sounds like a class you do not want to have.