Item change tracking in DynamicData

Since ReactiveUI’s ReactiveList<T> has recently been deprecated, I’ve been moving to DynamicData.

One feature I used from ReactiveList was item change tracking. It might look something like this:

var myList = new ReactiveList<MyClass>();
myList.ChangeTrackingEnabled = true;
myList.ItemChanged
	.Where(x => x.PropertyName == nameof(MyClass.SomeProperty))
	.Select(x => x.Sender)
	.Subscribe(myObject =>
	{
		// Do some stuff
	});

In DynamicData it goes like this:

var myList = new SourceList<MyClass>();
myList
	.Connect()
	.WhenPropertyChanged(myObject => myObject.SomeProperty)
	.Subscribe(propValue =>
	{
		MyClass myObject = propValue.Sender;
		string newValue = propValue.Value;
		// Do some stuff
	});

There is also WhenValueChanged, which just gives you the new property value as a straight IObservable:

myList
	.Connect()
	.WhenValueChanged(myObject => myObject.SomeProperty)
	.Subscribe(newValue =>
	{
		// Do some stuff
	});

The most powerful is WhenAnyPropertyChanged, which can tell you when any of the properties changed:

var myList = new SourceList<MyClass>();
myList
	.Connect()
	.WhenAnyPropertyChanged()
	.Subscribe(myObject =>
	{
		// Do stuff with myObject
	});

Or when any set of specified properties has changed:

var myList = new SourceList<MyClass>();
myList
	.Connect()
	.WhenAnyPropertyChanged(nameof(MyClass.FirstProperty), nameof(MyClass.SecondProperty))
	.Subscribe(myObject =>
	{
		// Do stuff with myObject
	});

5 Replies to “Item change tracking in DynamicData”

Jason Great says:

May 23, 2019 at 12:17 pm

WhenAnyPropertyChanged is not available even after I

using DynamicData;
using DynamicData.Binding;
using ReactiveUI;
using ReactiveUI.Fody.Helpers;
using System;
using System.Reactive;
using System.Reactive.Linq;
using System.Threading.Tasks;

Reply
1. RandomEngy says:
  
  May 23, 2019 at 1:54 pm
  
  Are you calling it on an IObservable after .Connect()? The extension method is in the DynamicData namespace on the latest version.
  
  Reply
Jason Great says:

May 23, 2019 at 5:20 pm

I find out I need to implement INotifyPropertyChanged before it is available. I also use PropertyChanged.Fody. However, I am still stuck.

private SourceList _myList { get; set; } = new SourceList();

_myList.Connect()
.ObserveOn(RxApp.MainThreadScheduler)
//.ObserveOnDispatcher()
.Bind(_targetCollection)
.Subscribe();

_myList.Connect()
.WhenAnyPropertyChanged()
.Subscribe( t =>
{
Debug.Print( t.customerName);
}
);

which is attach to a winform grid. After making some change to an item in the grid, I expect I can find out which item has been changed, but it doesn’t seem to do anything. Yet, I can see the item has been changed in _myList.

Can u provide me with a quick example of how this is done?

Reply
1. Jason Great says:
  
  May 23, 2019 at 6:08 pm
  
  I don’t know what happened.
  
  So I go ahead and remove the PropertyChanged.Fody package, and also the INotifyPropertyChanged.
  
  Now everything is working as expected, WhenAnyPropertyChanged is still available.
  
  _myList.Connect()
  .WhenAnyPropertyChanged()
  .Subscribe( t =>
  {
  Debug.Print( t.customerName);
  }
  );
  
  did tell me which item get changed as expected. Nice. Thanks a lot for your help
  
  Reply
Jason Great says:

June 5, 2019 at 1:16 pm

Tracking change is good. However, is it possible I can get a list of changes when someone click a button like this?

OKCmd = ReactiveCommand.Create(() =>
{
// Status = $”{EnteredText} is saved.”;
var change = _myList
.Connect()
.QueryWhenChanged(
{
}
);

// );
}

I was hoping var change will contain a list of changes (how about new item?) so I can save the changes back to a database.

Thanks.

Reply