title: Viewmodel doesn't exist in namespace
body: <p>I'm sorry if this is a stupid question or doesn't even fall under what I'm asking, but I'm new to WPF and I can't seem to get the hang of it.  Right now I'm doing something akin to <a href="https://www.c-sharpcorner.com/article/use-inotifypropertychanged-interface-in-wpf-mvvm/" rel="nofollow noreferrer">https://www.c-sharpcorner.com/article/use-inotifypropertychanged-interface-in-wpf-mvvm/</a> and I've run into a problem.  When I try to execute my code:</p>
  
  <pre><code>namespace DPS_Calculator_Prototype
  {
      /// &lt;summary&gt;
      /// Interaction logic for MainWindow.xaml
      /// &lt;/summary&gt;
      public partial class MainWindow : Window
      {
          public MainWindow() {
              InitializeComponent();
              }
      }
      public class NotifyPropertyChanged : INotifyPropertyChanged
      {
          public event PropertyChangedEventHandler PropertyChanged;
          public void RaisePropertyChange(string propertyName) {
              PropertyChanged?.Invoke(this, new 
  PropertyChangedEventArgs(propertyName));
          }
      }
  
  
          public class Calculator: NotifyPropertyChanged
          {
              private string _damage;
              public string Damage {
                  get { return _damage; }
                  set {
                      _damage = value;
                      RaisePropertyChange("Damage");
                  }
              }
          }
  
      namespace UseOf_INotifyPropertyChanged
      {
          public class MainWindowViewModel : Calculator
          {
              public MainWindowViewModel() {
                  Damage = "7";
              }
          }
      }
  }
  </code></pre>
  
  <p>I get the error that "The type or namespace name 'ViewModel' does not exist in the namespace 'DPS_Calculator_Prototype.UseOf_INotifyPropertyChanged' (are you missing an assembly reference?)" 
  and 
  "The name "MainWindowViewModel" does not exist in the namespace 'clr-namespace:DPS_Calculator_Prototype.UseOf_INotifyPropertyChanged.ViewModel'."
  and
  "The type 'VM:MainWindowViewModel' was not found. Verify that you are not missing an assembly reference and that all referenced assemblies have been built."
  I get the first error twice, once in MainWindow.g.cs and another in MainWindow.xaml.  The other two are all in MainWindow.XAML If anyone can tell me what I'm doing wrong then that would be great.  Here's the XAML file:</p>
  
  <pre><code>&lt;Window x:Class="DPS_Calculator_Prototype.MainWindow"
      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:VM="clr-namespace:DPS_Calculator_Prototype.UseOf_INotifyPropertyChanged.ViewModel"
      xmlns:local="clr-namespace:DPS_Calculator_Prototype"
      mc:Ignorable="d"
      Title="MainWindow" Height="450" Width="800"&gt;
  
      &lt;Window.DataContext&gt;
          &lt;VM:MainWindowViewModel x:Name="VMMainWindow"&gt;
          &lt;/VM:MainWindowViewModel&gt;
      &lt;/Window.DataContext&gt;
  
      &lt;Grid&gt;
          &lt;TextBox HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" 
           Text="{Binding Damage}" VerticalAlignment="Top" Width="120" 
           Margin="78,28,0,0" TextChanged="TextBox_TextChanged"/&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>