C#•2y ago

Unmanaged struct backed INPC ViewModel, only raising PropertyChanged when backing field(s) changed

So, suppose we have a large unmanaged struct that we obtain from external source, suppose from a network resource. This unmanaged struct decomposes into a set of primitives, with various values.

public struct ExampleStruct
{
  public int StructId;
  public float StructRealAmount;
  public DateTimeOffset StructTimestamp;
}

public struct ExampleStruct
{
  public int StructId;
  public float StructRealAmount;
  public DateTimeOffset StructTimestamp;
}

and then we have our ViewModel class that implements INotifyPropertyChanged. I have made an example below, not using the above struct as a field.

public class ExampleViewModel : INotifyPropertyChanged 
{
  // INPC boilerplate, to be replaced perhaps with an MVVM toolkit later
  public event PropertyChangedEventHandler? PropertyChanged;
  public void OnPropertyChanged(string propertyName)
  {
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
  public static bool CheckChange<T>(ref T oldValue, T newValue, [CallerMemberName] string propertyName = "")
  {
    if (!Equals(oldValue, newValue))
    {
      oldValue = newValue;
      OnPropertyChanged(propertyName);
      return true;
    }
    return false;
  } 
  // end INPC boilerplate

  private int _viewModelId;
  public int ViewModelId { get => _viewModelId; set => CheckChange(ref _viewModelId, value); }
  private float _viewModelRealAmount;
  public float ViewModelRealAmount { get => _viewModelRealAmount; set => CheckChange(ref _viewModelRealAmount, value); }
  private DateTimeOffset _viewModelTimestamp;
  public DateTimeOffset ViewModelTimestamp { get => _viewModelTimestamp; set => CheckChange(ref _viewModelTimestamp, value); }

  // TODO: On receive ExampleStruct, set properties to fire events if data has changed
}

public class ExampleViewModel : INotifyPropertyChanged 
{
  // INPC boilerplate, to be replaced perhaps with an MVVM toolkit later
  public event PropertyChangedEventHandler? PropertyChanged;
  public void OnPropertyChanged(string propertyName)
  {
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
  public static bool CheckChange<T>(ref T oldValue, T newValue, [CallerMemberName] string propertyName = "")
  {
    if (!Equals(oldValue, newValue))
    {
      oldValue = newValue;
      OnPropertyChanged(propertyName);
      return true;
    }
    return false;
  } 
  // end INPC boilerplate

  private int _viewModelId;
  public int ViewModelId { get => _viewModelId; set => CheckChange(ref _viewModelId, value); }
  private float _viewModelRealAmount;
  public float ViewModelRealAmount { get => _viewModelRealAmount; set => CheckChange(ref _viewModelRealAmount, value); }
  private DateTimeOffset _viewModelTimestamp;
  public DateTimeOffset ViewModelTimestamp { get => _viewModelTimestamp; set => CheckChange(ref _viewModelTimestamp, value); }

  // TODO: On receive ExampleStruct, set properties to fire events if data has changed
}

I had a thought to in the View Model class just have a single field of the unmanaged struct, and then fire off events of property changed. But if I were to do that, how would one determine which properties were changed ? Would it be better to have the unmanaged struct as the sole backing field, or should I not do that?

2 Replies

RazorSharpFang•2y ago

I have decided to not do that, and set each property in turn, which is only raise the property changed events for that property efficiently, whereas having a single backing field would make raising the events more difficult.

Accord•2y ago

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Unmanaged struct backed INPC ViewModel, only raising PropertyChanged when backing field(s) changed