MVVM.VBSourceGenerators

The CommunityToolkit.MVVM source generators only work in C#. This package augments the toolkit to allow some of the generators to work for VB.NET.

Working

• <ObservableProperty>
  • Generates a public property with OnPropertyChanged notification as well as most helper methods defined as per the CommunityToolkit.
• <NotifyPropertyChangedFor(NameOf(T))>
  • Generates a property with change notification for existing properties.
• <RelayCommand>
  • Can decorate Sub, Async Sub, or Async Function
  • Supports CanExecute callback functionality
  • Supports parameter passthrough
  • Supports CancellationToken for async commands
  • Supports all RelayCommand attribute properties from the CommunityToolkit.MVVM library, except for the CanExecute property
    • CanExecute is defined by simply naming a Sub Can[MethodName].
• NotifyCanExecuteChangedFor(NameOf(T))
  • Use on an ObservableProperty marked field to automatically notify the CanExecute state of a command when the property changes.
• NotifyPropertyChangedRecipients
  • Use on an ObservableProperty marked field to send a message when the property changes
  • Does not support use on existing properties, only on generated properties.
• AttachAttribute
  • Custom implementation of the [property: Attribute] C# usage for VB.NET
  • Passthrough attributes to the generated property by annotating the field/method with e.g <AttachAttribute(GetType(JsonIgnoreAttribute))>.
  • If an attached attribute requires a parameter, it must be passed into AttachAttribute as a fully qualified string instead.

Planned

• Property Validation Attributes
• INotifyPropertyChanged Attribute
• Custom Attributes

Installation

1. Add the NuGet package for MVVM.VBSourceGenerators to your VB.NET project:

   dotnet add package IridiumIO.MVVM.VBSourceGenerators

2. Ensure that you also reference CommunityToolkit.MVVM in your project.

ObservableProperty Usage

1. In your VB.NET ViewModel, use the [ObservableProperty] attribute as you would in C#
2. Make sure your fields follow the naming convention of starting with an underscore (e.g., _name).
3. You can then use the generated Uppercase property Name in your code.

Example 1:

Imports CommunityToolkit.Mvvm.ComponentModel

Partial Public Class MyViewModel
    Inherits ObservableObject

    <ObservableProperty>
    Private _name As String
End Class

 

Example 2: Including NotifyPropertyChangedFor

Imports CommunityToolkit.Mvvm.ComponentModel

Partial Public Class PersonViewModel
    Inherits ObservableObject

    <ObservableProperty>
    <NotifyPropertyChangedFor(NameOf(FullName))>
    Private _firstName As String

    <ObservableProperty>
    <NotifyPropertyChangedFor(NameOf(FullName))>
    Private _lastName As String

    Public ReadOnly Property FullName As String
        Get
            Return $"{FirstName} {LastName}"
        End Get
    End Property

End Class

Additional Features:

• As defined here, additional methods for On[Name]Changed and On[Name]Changing are also generated as partial methods and can be included.

RelayCommand Usage

1. In your VB.NET ViewModel, use the [RelayCommand] attribute as you would in C# on a method.

Examples:

Imports CommunityToolkit.Mvvm.ComponentModel

Partial Public Class MyViewModel
    Inherits ObservableObject

    <RelayCommand>
    Private Sub Save()
        ' Save logic here
    End Sub

    <RelayCommand>
    Private Sub SelectItem(item As String)
        ' Logic to select an item
    End Sub

    'Will generate two commands:
    'LoadDataAsyncCommand and CancelLoadDataAsyncCommand
    <RelayCommand(IncludeCancelCommand:=True)>
    Private Async Function LoadDataAsync(ctx As CancellationToken) As Task
        ' Load data logic here
        Await Task.Delay(1000) ' Simulating async work
    End Function

End Class

 

Example 2: Including CanExecute callback

By creating a function that returns a Boolean and prefixing it with Can, you can control whether the command can execute.

Imports CommunityToolkit.Mvvm.ComponentModel

Partial Public Class PersonViewModel
    Inherits ObservableObject

    <RelayCommand>
    Private Sub SaveData()
        ' Logic to save data
    End Sub

    Private Function CanSaveData() As Boolean
        ' Logic to determine if saving is allowed
         Return MyData.Count > 0
    End Function

End Class