10 MVVM Toolkit

What is MVVM Toolkit

• The CommunityToolkit.Mvvm is a free, open-source library maintained by Microsoft and the .NET community.
• It provides a set of helpers and base classes to implement the MVVM pattern in WPF applications efficiently. It helps you write cleaner C# code for WPF applications, especially when working with data binding, buttons, commands, and updating the UI when values change.

RelayCommand

• RelayCommand is a simple way to connect a button to a method in your ViewModel without writing a click event in the code-behind.
• This allow as to move the logic from the code-behind to the ViewModel, keeping the UI and business logic separate.
• Relay command is not built into WPF by default. You need to implement it yourself or use a library like MVVM Light or CommunityToolkit.Mvvm.

Original Button Code

```xml
<Button Content="Save" Click="SaveButton_Click"/> 
```
```csharp
private void SaveButton_Click(object sender, RoutedEventArgs e)
{
    MessageBox.Show("Client saved!");
}
```

Button with RelayCommand

• Here save button bind to the SaveCommand property in the ViewModel.

  <Button Content="Save" Command="{Binding SaveCommand}"/>
  

  public RelayCommand SaveCommand { get; }
  
  public ViewModel()
  {
      SaveCommand = new RelayCommand(SaveClient);
  }
  
  private void SaveClient()
  {
      MessageBox.Show("Client saved!");
  }
  

RelayCommand

• RelayCommand is a generic version of RelayCommand that allows you to pass a parameter to the command.
• The parameter type is specified by the generic type T.

<Button Content="Save" Command="{Binding SaveCommand}" CommandParameter="{Binding SelectedClient}"/>

public RelayCommand<Client> SaveCommand { get; }

public ViewModel()
{
    SaveCommand = new RelayCommand<Client>(SaveClient);
}

private void SaveClient(Client client)
{
    MessageBox.Show($"Client {client.Name} saved!");
}

ObservableObject

• ObservableObject is a base class that implements the INotifyPropertyChanged interface. and allows your ViewModel to notify the UI when a property value changes.

  public partial class Client : ObservableObject
  {
      [ObservableProperty]
      private string name = "";
  
      [ObservableProperty]
      private double rate;
  }
  

  <StackPanel>
      <TextBox Text="{Binding Name,
                      UpdateSourceTrigger=PropertyChanged}" />
  
      <TextBlock Text="{Binding Name}" />
  </StackPanel>
  

ObservableProperty

• ObservableProperty is an attribute that you can apply to a private field in a class that inherits from ObservableObject. It automatically generates a public property with getter and setter, and raises the PropertyChanged event when the value changes.

  public partial class Client : ObservableObject
  {
      [ObservableProperty]
      private string name = "";
  
      [ObservableProperty]
      private double rate;
  }
  

ObservableRecipient

ObservableValidator