WPF C# MVVM Radio Button load list content

You must create a structure of a list of questions, where each question has a list of possible answers.

The following example uses the RelayCommand implementation provided by Microsoft Docs: Relaying Command Logic. It uses a composed data model consisting of Question and Answer:

Question.cs

public class Question : INotifyPropertyChanged
{
  public Question(string summary, Answer answer)
  {
    this.Summary = summary;
    this.Answer = answer;
  }

  public string Summary { get; set; }
  public Answer Answer { get; set; }

  public event PropertyChangedEventHandler PropertyChanged;
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
}

Answer.cs

public class Answer : INotifyPropertyChanged
{
  public Answer(IEnumerable<IChoice> choices)
  {
    this.Choices = choices;
  }

  // Evaluates the answer(s)
  public bool Validate()
  {
    this.IsCorrect = this.Choices.All(
      choice => choice.IsValidChoice && choice.IsSelected 
                || !choice.IsValidChoice && !choice.IsSelected);
    return this.IsCorrect;
  }

  public ICommand CheckAnswerCommand =>
    new RelayCommand(answer => Validate());
  
  public IEnumerable<IChoice> Choices { get; set; }

  private bool isCorrect;
  public bool IsCorrect
  {
    get => this.isCorrect;
    private set
    {
      this.isCorrect = value;
      OnPropertyChanged();
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
}

IChoice

public interface IChoice : INotifyPropertyChanged
{
  // Marks whether the choice is a valid answer
  bool IsValidChoice { get; }

  // Selects the choice as an answer
  bool IsSelected { get; set; }

  string Text { get; set; }
}

MultiChoice.cs

class MultiChoice : IChoice
{
  public MultiChoice(string text, bool isValidChoice)
  {
    this.Text = text;
    this.IsValidChoice = isValidChoice;
  }

  #region Implementation of IChoice

  public bool IsValidChoice { get; }

  private bool isSelected;    
  public bool IsSelected
  {
    get => this.isSelected;
    set
    {
      this.isSelected = value;
      OnPropertyChanged();
    }
  }

  private string text;    
  public string Text
  {
    get => this.text;
    set
    {
      this.text = value;
      OnPropertyChanged();
    }
  }

  #endregion

  #region Implementation of INotifyPropertyChanged

  public event PropertyChangedEventHandler PropertyChanged;
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }

  #endregion
}

SingleChoice.cs

class SingleChoice : IChoice
{
  public SingleChoice(string text, bool isValidChoice)
  {
    this.Text = text;
    this.IsValidChoice = isValidChoice;
  }

  #region Implementation of IChoice

  public bool IsValidChoice { get; }    
  
  private bool isSelected;    
  public bool IsSelected
  {
    get => this.isSelected;
    set
    {
      this.isSelected = value;
      OnPropertyChanged();
    }
  }

  private string text;    
  public string Text
  {
    get => this.text;
    set
    {
      this.text = value;
      OnPropertyChanged();
    }
  }

  #endregion

  #region Implementation of INotifyPropertyChanged    

  public event PropertyChangedEventHandler PropertyChanged;    
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }

  #endregion
}

ViewModel.cs

public class ViewModel : INotifyPropertyChanged
{
  public ObservableCollection<Question> Questions { get; set; }

  public ViewModel()
  {
    this.Questions = new ObservableCollection<Question>
    {
      new Question(
        "Which number follows '1'?",
        new Answer(
          new[]
          {
            new SingleChoice("3", false), 
            new SingleChoice("15", false), 
            new SingleChoice("2", true),
            new SingleChoice("7", false)
          })),
      new Question(
        "Which creature can fly?",
        new Answer(
          new[]
          {
            new MultiChoice("Bird", true),
            new MultiChoice("Elephant", false),
            new MultiChoice("Bee", true),
            new MultiChoice("Cat", false)
          }))
    };
  }

  public event PropertyChangedEventHandler PropertyChanged;
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
}

MainWindow.xaml

<Window xmlns:system="clr-namespace:System;assembly=mscorlib">
  <Window.DataContext>
    <ViewModel />
  </Window.DataContext>

  <StackPanel>
    <CheckBox Content="Answer 1 is Correct?" IsChecked="{Binding Questions[0].Answer.IsCorrect, Mode=OneWay}" />
    <CheckBox Content="Answer 2 is Correct?" IsChecked="{Binding Questions[1].Answer.IsCorrect, Mode=OneWay}" />
    <ListBox ItemsSource="{Binding Questions}">
      <ListBox.ItemTemplate>
        <DataTemplate DataType="{x:Type viewModels:Question}">
          <StackPanel>
            <TextBlock Text="{Binding Summary}" />
            <ListBox ItemsSource="{Binding Answer.Choices}">
              <ListBox.Resources>
                <DataTemplate DataType="{x:Type viewModels:SingleChoice}">
                  <RadioButton Content="{Binding Text}" 
                               GroupName="Answer"
                               IsChecked="{Binding IsSelected}"
                               Command="{Binding RelativeSource={RelativeSource AncestorType=ListBox}, Path=DataContext.Answer.CheckAnswerCommand}" />
                </DataTemplate>
                <DataTemplate DataType="{x:Type viewModels:MultiChoice}">
                  <CheckBox Content="{Binding Text}" 
                            IsChecked="{Binding IsSelected}"
                            Command="{Binding RelativeSource={RelativeSource AncestorType=ListBox}, Path=DataContext.Answer.CheckAnswerCommand}" />
                </DataTemplate>
              </ListBox.Resources>
            </ListBox>
          </StackPanel>
        </DataTemplate>
      </ListBox.ItemTemplate>
    </ListBox>
  </StackPanel>
</Window>