Get old selected value instead of new selected value from comboBox in MVVM application

Describe the bug

I use avalonia to build a MVVM application, using a comboBox to select items. I set selectedItem with viewmoel binding ,set a reactivecommand for handle SelectionChanged event and bind this event. But when i select other item from combobox , in command for handle event , i got the old selected value instead of the new selected value. I write a exmaple application to show the bug. Here are view code and viewmodel code .

To Reproduce

Steps to reproduce the behavior:

1.Clone the code , build and run the example application 2.Select any item in comboBox , for example First , you can see the textBlock’s text is "Current Selected " 3.Select another item in comboBox ,for example Second you can see the textBlock’s text is “Current Selected First”

the setp 2 and 3 can reproduce the behavior , because the event for command get the old selected value rather than new selected value.

Expected behavior

I can get the new selected value when SelectionChanged event is raised.

Screenshots

the application startup

step 2

step 3

Desktop (please complete the following information):

• OS: Windows 10 Perfessional 21H2
• Version 0.10.19

Additional context

I try to debug it , and i found afrer the selectedItem changed , the control raise the SelectionChanged event first the update the selectedItem to new value. I guess the occurrence of bugs is related to the order of execution. But i couldn’t write a correct test in Avalonia.Controls.UnitTests to prove the bug is exist and code change is right. I have no idea to write a binding code equal to axaml binding like this in test . This is the unfinished test code I wrote

        [Fact]
        public void Binding_SelectionChanged_Event()
        {
            var inputManagerMock = new Moq.Mock<IInputManager>();
            var services = TestServices.StyledWindow.With(inputManager: inputManagerMock.Object, keyboardDevice: () => new KeyboardDevice());

            using (UnitTestApplication.Start(TestServices.StyledWindow))
            {
                var window = new Window();
                var target = new ComboBox()
                {
                    Items = { "First", "Second", "Third", "Fourth" },
                    SelectedIndex = -1,
                    Template = GetTemplate(),
                };
                string recordText = null;
                string bindText = null;//the variable need to bind

                target.SelectionChanged += (sender, args) =>
                {

                };

                window.Content = target;

                target.Focus();

                target.RaiseEvent(new KeyEventArgs
                {
                    RoutedEvent = InputElement.KeyDownEvent,
                    Key = Key.Down,
                });


                target.RaiseEvent(new KeyEventArgs
                {
                    RoutedEvent = InputElement.KeyDownEvent,
                    Key = Key.Down,
                });

                Assert.True(recordText == target.SelectionBoxItem.ToString());
            }
        }

[timunie]

Otherwise you will need to wait for someone to have a time for it to do.

[timunie]

No a fix if you are able to fix it.