Should my Models have Observable Properties?

[Peaj]

Problem

I am just starting out with MAUI and was using the MVVM Community Toolkit as recommended in various tutorials.
I was pretty happy with my Model logic being completely clean and not using any MAUI specific code at all.

But than I encountered the problem that observing a complete object does not work as I expected.

[ObservableProperty]
private WorkTimeTracker workTimeTracker = new();

Using this code and Binding to WorkTimeTracker.StartTime does not seem to update the UI parts that are displaying WorkTimeTracker .WorkTime etc.

Solution?

I can only see two solutions to this problem:

1) Using observable property attributes in the Model

• Dirties the Model code with MAUI specific attributes
• Binding to WorkTimeTracker .StartTime also raises the question whether the View should know about the Model at all

2) Wrap every Model property in a ViewModel property and call OnPropertyChanged

public partial class EditWorkTimesViewModel : BaseViewModel
{
  ...
  public TimeSpan WorkTime
  {
      get => this.WorkTimeTracker.WorkTime;
      set
      {
          this.WorkTimeTracker.WorkTime = value;
          OnPropertyChanged(nameof(WorkTimeTracker));
          OnPropertyChanged(nameof(StartTime));
      }
  }
  ...
}

• Seems to get pretty tedious
• Has the problem that you need to know the implementation details of WorkTimeTracker in the ViewModel to know what changed

Maybe I am just missing something here. But most of the Tutorials seem to just stop before the Model gets too complex.
Or maybe I am just being too puristic here?

[ne0rrmatrix]

If you are trying to update an object inside a ObservableCollection after page has loaded you can try something like the following.
Here is an example using community toolkit for Maui.

namespace NerdNewsNavigator2.Model;

/// <summary>
/// A class for storing <see cref="Download"/> in a Database.
/// </summary>
[Table("Downloads")]
public partial class Download : ObservableObject
{
   [PrimaryKey, AutoIncrement, Column("Id")]
    public int Id { get; set; }
    [ObservableProperty]
    private string _copyRight;
    [ObservableProperty]
    private string _fileName;
    [ObservableProperty]
    private bool _deleted;
}

That above is part of model file that I use. Also adding:

 /// <summary>
    /// An <see cref="ObservableCollection{T}"/> of downloaded <see cref="Download"/> managed by this class.
    /// </summary>
    [ObservableProperty]
    private ObservableCollection<Download> _downloadedShows;

Adding [ObserrvableProperty] lets you dynamically update an observable object or observable collection. Just adding observable will not apply property changed outside of adding or removing an item to it. If you want to update properties of a collection you need to add observable property to both the collection and model.

[Peaj]

Thank you for your answer.
I was not asking about ObservableCollections though.

Maybe I was not specific enough about my model.
WorkTimeTracker is my model class and I was asking if I should/have to use [ObservableProperty] inside this model class.
I was under the impression that I could manage all the bindings in the view model which would leave the model nice and clean
with no MAUI specific dependencies.

From your answer I can see that you are using [ObservableProperty] in your models class.
I have also since found some code examples doing the same so it seems to be the way to go.

Although in your case of using an ObservableCollection I am wondering if it wouldnt be more MVVM conform to have a DownloadViewModel for each list item because you are technically skipping the view model when binding to download.FileName etc.
Sometimes there may even be UI specific data to be stored with the list items like "IsSelected" etc.

[ne0rrmatrix]

Sorry about the confusion. I am using a collection view to display a list of items that are wrapped in Observable collection. I have to update the properties in the collection itself from an event that is in a background process.

share some model data across pages. An example is I have a button you can click to download a show from a podcast. That show can appear on the most recent show list, which is on a different page. I have a cancel button that appears once download start. The show also has download button go away and so does cancel button when download completes.

When you click on download it spawns a background thread that starts the download and uses events to update the relevant button on what ever page I am on for the current item in the observable collection I am using. So updating an item in collection that is being actively updated from a background process is what I need to do. So decorating the model with [ObservableProperty] was the first solution I came across that worked.

[Peaj]

I see. The background thread might make it trickier. But I guess there should still be a way to wire it up via a DownloadViewModel that is shared across your pages. For now I also put [ObservableProperty] attributes in my model to get it to work. But I will see if I can get rid of them in the future.

[sjordanGSS]

Of the two options presented, I've often taken the second route. Although tedious it's pretty straightforward and provides an opportunity to pull in data from other sources when creating the ViewModel.

As an aside for something I've seen elsewhere in this thread, you don't need an ObservableProperty for an ObservableCollection<T>. It's more efficient to do something like

public ObservableCollection<string> Strings { get; } = new();

so it only gets bound to once and then use Add() and Clear() than it is to keep creating and binding to new ObservableCollections. You can even use Mode=OneTime on the Binding in this case to make that a little bit more efficient as well.

[Peaj]

Thanks for the insight.
That would also mean that the list item should be a view model and not the model directly.
Interestingly most MVVM examples just seem to ignore that.

[SalKly]

I am just starting out with MAUI and I have the same exact question so is still using [ObservableProperty] inside of the model is the way to go ? it doesn't feel right D: