What is the function of Message sender in xamarin.forms - xamarin

Question

What is the function of Message sender in xamarin.forms? In my app I have cart contain list view and a Grant Total label. Is it possible to update the label using message sender? I can get the total amount from my sqlite db I need to update it to the view.
This is my number picker index change event in view cell
numPicker.SelectedIndexChanged += (sender, args) =>
{
// var price = _cartQuery.GetSum();
sender = BindingContext;
// cm_items item = (cm_items)sender;
if(Int32.Parse(btn_NumBtn.Text)<=1)
{
lbl_Price.Text = ((numPicker.SelectedIndex + 1) * (Int32.Parse(lbl_Price.Text))).ToString();
btn_NumBtn.Text = (numPicker.SelectedIndex + 1).ToString();
}
else
{
int a = Int32.Parse(lbl_Price.Text);
int b = Int32.Parse(btn_NumBtn.Text);
int c = a / b;
lbl_Price.Text = ((numPicker.SelectedIndex + 1) * c).ToString();
btn_NumBtn.Text = (numPicker.SelectedIndex + 1).ToString();
}
_cartQuery.UpdatePicker((BindingContext as CartDB).Cart_Item_Id, numPicker.SelectedIndex + 1, Int32.Parse(lbl_Price.Text));
price = _cartQuery.GetSum();
// App.Instance.ViewModel.TotalAmount = price;
// _cartDB.total = App.Instance.ViewModel.TotalAmount;
Calculate_price();
numPicker.IsEnabled = false;
};
Calculate_price method
public double Calculate_price()
{
try
{
var price = 0;
price = _cartQuery.GetSum();
App.Instance.ViewModel.TotalAmount = price;
return price;
}
catch (Exception ex)
{
throw ex;
}
}
In my view i have a label named grant total, i need to update the total on e number picker change
Label lbl_amnt = new Label
{
// Text = viewModel.Price.ToString(),
// Text=CartCell.price.ToString(),
Text = price.ToString(),
FontSize = 18,
FontAttributes = FontAttributes.Bold,
TextColor = Color.FromRgb(102, 204, 102),
VerticalOptions = LayoutOptions.CenterAndExpand,
HorizontalOptions = LayoutOptions.EndAndExpand,
};
lbl_amnt.SetBinding(Label.TextProperty, "TotalAmount");
update to my post as per the comment from #Grish
In my view model i have this TotalAmount as a property
public double _TotalAmount;
public double TotalAmount
{
get { return _TotalAmount; }
set { _TotalAmount = value; OnPropertyChanged("TotalAmount");}
}
I think the better solution is i notify but the thing is view is not binding

Answer 1

Binding is definitely the answer in your case. I think the problem is that you bind string (label's text) to property of type double.
You should specify IValueConverter or stringFormat parameters in your call to SetBinding.
Check this link:
https://forums.xamarin.com/discussion/19146/binding-to-integers