01_generate_a_viewModel.md

Generate a ViewModel

In this article you learn everything about generating a ViewModel:

1. Install the MvvmGen NuGet package
2. Generate your first ViewModel
3. Look at the Generated Code

Install the MvvmGen NuGet Package

To get started with MvvmGen, install the NuGet Package MvvmGen

dotnet add package MvvmGen

After that, you are ready to generate a ViewModel.

Generate Your First ViewModel

To generate a ViewModel with MvvmGen, you define a partial class in your code and you add the ViewModel attribute to it:

using MvvmGen;

namespace MyWpfApp.ViewModel
{
  [ViewModel]
  public partial class EmployeeViewModel
  {
  }
}

The ViewModel attribute tells MvvmGen's ViewModelGenerator to generate a partial EmployeeViewModel class that looks like below. This generation happens on-the-fly while you type in your code editor.

using MvvmGen.Commands;
using MvvmGen.Events;
using MvvmGen.ViewModels;

namespace MyWpfApp.ViewModel
{
    partial class EmployeeViewModel : ViewModelBase
    {
        public EmployeeViewModel()
        {
            this.OnInitialize();
        }

        partial void OnInitialize();
    }
}

As you can see, the generated class inherits from ViewModelBase. ViewModelBase is MvvmGen's base class for ViewModels. It implements the INotifyPropertyChanged interface that defines the PropertyChanged event, and it has a protected OnPropertyChanged method to raise that event from subclasses.

Note: You can also inherit your class directly or indirectly from ViewModelBase. Then the generated class won't inherit from ViewModelBase. This allows you to define custom base classes for your ViewModels.

The generated ViewModel class in the code snippet above has also a constructor. From that constructor a partial method with the name OnInitialize is called. You can implement this partial method in your code if you want to add some initialization logic:

[ViewModel]
public partial class EmployeeViewModel
{
  partial void OnInitialize()
  {
    // Add initialization logic here
  }
}

Look at the Generated Code

In Visual Studio, you can navigate to the generated code via the Solution Explorer. Expand Dependencies->Analyzers, and there you find MvvmGen.SourceGenerators. Expand this node and also the MvvmGen.ViewModelGenerator, and then you'll find there the generated EmployeeViewModel.g.cs file, prefixed with the namespace like you see it in the following screenshot:

You can keep that generated file open side-by-side with your file to see how the code is generated on-the-fly.

Important to understand is that this generated file is generated as part of the compilation of your project. It will work as well if you build your project for example on the command line with the .NET CLI via

dotnet build

Also with the .NET CLI the code generation will be executed and the generated code gets compiled into your project. So, it's always generated for you.

Now, with the ViewModel ready, let's create some properties.