BindablePicker | Picker for Xamarin.Forms to ease programming MVVM paradigm | Form library

The following example uses an MVVM approach to update a property based on a picker selection:

https://github.com/xamarin/xamarin-forms-samples/blob/master/UserInterface/BindablePicker/BindablePicker/BindablePicker/SimpleColorPickerPageViewModel.cs

It uses OnPropertyChanged("SelectedColor"); when the selection changes to update another property.

I have two questions:

Firstly, is there any advantage of using this approach over the normal OnSelectedIndexChanged event in the xaml.cs?

Secondly how would i use this approach if i wanted to update a particular item for my custom object in my viewmodel. For example, if the selected item changed in the above example, store the value in another object in the view model?

It just seems long winded to the OnSelectedIndexChanged approach, but guessing there are advantages i'm unaware of?

basicaly i have a number of dropdowns on a page, and with each change, i want to update the object in my view model which will be sent back to the server with a rest service.

I have a xaml file where I put the picker in and a code behind to populate it. The code used below:

The following example works fine (https://developer.xamarin.com/samples/xamarin-forms/UserInterface/BindablePicker/)

When i try to implement it in my code, the object referenced for selectedItem is not being set. The picker is loading and selecting data fine, just not updating the object.

Here is some of the code i'm using: XAML Page

I'm currently using a xamarin forms picker and the example fworks fine as it's a List. (https://developer.xamarin.com/samples/xamarin-forms/UserInterface/BindablePicker/)

I need to bind it to a custom type:

In xaml in Xamarin.Forms, I have a custom control, I want to add property of type int. I think I have to use Bindable properties, so later I can bind a property from ViewModel.

I found this topic, but I'm not sure how to use it.. there is: