PowerShell Observable Collection Event

Question

I am trying to register the PropertyChanged event for an Observable Collection in PowerShell, but no dice. This works just fine for the CollectionChanged event.

This works:

Register-ObjectEvent -InputObject $MyObservableCollection -EventName CollectionChanged -Action {Write-Host "Collection changed!"}`

Whereas this does not work:

Register-ObjectEvent -InputObject $MyObservableCollection -EventName PropertyChanged -Action {Write-Host "Property changed!"}`

The error I receive is as follows:

Register-ObjectEvent : Cannot register for the specified event. An event with the name 'PropertyChanged' does not exist.

Answer 1

Looks like you need to create a class that support the Property changed, so you could do something like this:

$PersonClass = @'
using System.ComponentModel;

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string _Name;
    public string Name
    {
        get { return _Name; }
        set
        {
            _Name = value;

            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("Name"));
        }
    }

    private string _Age;
    public string Age
    {
        get { return _Age; }
        set
        {
            _Age = value;

            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("Age"));
        }
    }

    private string _Country;
    public string Country
    {
        get { return _Country; }
        set
        {
            _Country = value;

            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("Country"));
        }
    }
}
'@
Add-Type -TypeDefinition $PersonClass -Language 'CSharp'
$NewPerson = [Person]::New()
$MyObservableCollection = New-Object -TypeName System.Collections.ObjectModel.ObservableCollection[Person]

Register-ObjectEvent -InputObject $NewPerson -EventName PropertyChanged -Action {Write-Host  "PropertyChanged on item"}
Register-ObjectEvent -InputObject $MyObservableCollection -EventName CollectionChanged -Action {Write-Host "Item added or removed"}

$MyObservableCollection.Add($NewPerson)
$NewPerson.Name = 'Joe Bloggs'

Here we are creating a Person class which stores the properties of a person like Name, Age and country, each with a PopertyChangedEventHandler. Once you have that its then creating an observable arraylist so you can add/remove individual Persons from the list (which will trigger the CollectionChanged event).