Stacklayout backgroundColor binding with MVVM - xaml

Question

I'm attempting to get my head around MVVM with XamarinForms and I'm slightly confused with regards to proper partitioning of functionality:
I have a main page, MainPage.xaml, which includes a stacklayout:
<StackLayout x:Name="MainPageStackLayout">
...
</StackLayout>
Within this stacklayout I have Picker which is bound as follows:
<Picker Title="Select a background colour"
TitleColor="Black"
TextColor="Black"
ItemsSource="{Binding MyColours}"
ItemDisplayBinding="{Binding Name}"
SelectedItem="{Binding selectedBackGroundColour}" SelectedIndexChanged="BackGroundColourPicker_SelectedIndexChanged"/>
Following the article from microsoft (https://learn.microsoft.com/en-us/samples/xamarin/xamarin-forms-samples/userinterface-monkeyapppicker/):
I have a "View" which basically defines the layout of my page.
A "ViewModel" which holds an IList "MyColours" and a variable "SelectedBackGroundColour".
A "Model" which defines the MyColour class. A MyColour has a string name and a Xamarin.Forms.Color (from a hex value, both populated on start up).
This all works fine. I can start up the app and the Picker populates with the colours I add to "MyColours". If I change the index then my SelectedBackGroundColour also updates, has the correct name and a different RGB value.
However, I'm lost as to where I would tie in the updating of the actual background colour of the MainPageStackLayout. The View (MainPage.xaml.cs) picks up the "BackGroundColourPicker_SelectedIndexChanged" event but what is the standard practice for reading from the view model (where SelectedBackGround colour is actual defined ?)
I have a feeling I can bind Background colour in the MainPageStackLayout xaml view so I wont have to catch the selected index change event.
Thanks all.

Answer 1

According to your description, I guess that you want to change MainPage StackLayout BackGround color by Picker value, am I right?
If yes, please follow the steps below.
Firstly, please confirm that you implement INotifyPropertyChanged interface to notify SelectedBackGroundColour changed.
Then there are full code, please take a look:
<StackLayout x:Name="MainPageStacklayout" BackgroundColor="{Binding selectedBackGroundColour.color}">
<Picker
x:Name="picker1"
Title="Select a background colour"
ItemDisplayBinding="{Binding name}"
ItemsSource="{Binding MyColours}"
SelectedItem="{Binding selectedBackGroundColour}"
TextColor="Black"
TitleColor="Black" />
</StackLayout>
public partial class Page5 : ContentPage, INotifyPropertyChanged
{
public ObservableCollection<MyColour> MyColours { get; set; }
private MyColour _selectedBackGroundColour;
public MyColour selectedBackGroundColour
{
get { return _selectedBackGroundColour; }
set
{
_selectedBackGroundColour = value;
RaisePropertyChanged("selectedBackGroundColour");
}
}
public Page5()
{
InitializeComponent();
MyColours = new ObservableCollection<MyColour>()
{
new MyColour(){name="red",color=Color.Red},
new MyColour(){name="gray",color=Color.Gray},
new MyColour(){name="BlueViolet",color=Color.BlueViolet}
};
selectedBackGroundColour = MyColours[0];
this.BindingContext = this;
}
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public class MyColour
{
public string name { get; set; }
public Color color { get; set; }
}
The screenshot: