Changes in DataSource not being reflected in UI - xamarin

Question

I'm doing a simple xamarin forms application where I have a TimeAttendance model, a list view page and a time entry page. When I select a time entry from the list it takes me to the add/edit page where I'm able to change all the dropdown/entry/timepicker values and it gets saved correctly.
The problem I'm having is that I'm calculating total hours based on start and end time. This value is getting saved correctly when I close the day but it's not updating in the UI even though the binding property is set. I can see in the backend code that the value gets updated but it's not reflected in the UI unless I close the day and open it again.
It looks like the binding from source to target it's only getting triggered on the first load, but I've been reading and these views are set to two-way binding by defualt.
xaml code:
<Label Text="Total Hours"/>
<Label x:Name="totalHours"
Text="{Binding TotalHours}"/>
<Button Text="CLOSE" Clicked="CloseDay_Clicked"/>
<Button Text="DELETE" Clicked="Delete_Clicked"/>
Code behind:
async void CloseDay_Clicked(object sender, EventArgs e)
{
var timeEntry = (TimeAttendance)BindingContext;
timeEntry.idUser = 1;
await App.Database.SaveTimeAttendanceAsync(timeEntry);
//await Navigation.PopAsync();
}
async void TimePicker_timeChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
if (e.PropertyName == TimePicker.TimeProperty.PropertyName)
{
var timeEntry = (TimeAttendance)BindingContext;
var totalHours = timeEntry.EndTime - timeEntry.StartTime;
timeEntry.TotalHours = totalHours.Hours + (totalHours.Minutes / 15) * 0.25;
}
}
The bindingContext is set form the list page:
async void OnListViewItemSelected(object sender, SelectedItemChangedEventArgs e)
{
await Navigation.PushAsync(new TimeAttendanceEntryPage
{
BindingContext = e.SelectedItem as TimeAttendance,
});
}
My timeattendance model:
public class TimeAttendance
{
[PrimaryKey, AutoIncrement]
public int ID { get; set; }
public int idUser { get; set; }
public DateTime Date { get; set; } = DateTime.Today;
public string Commodity { get; set; }
public string Exception { get; set; }
public string RequestType { get; set; }
public string RequestId { get; set; }
public TimeSpan StartTime { get; set; }
public TimeSpan EndTime { get; set; }
public string Activity { get; set; }
public double TotalHours { get; set; }
}
As I said, the code is working fine for updating values closing and saving, I just don't know why when I update TotalHours it gets saved correctly but I cannot see the change in the label that is binded directly to this value.

Answer 1

you just should let change your Timeattendance model,let it implement the INotifyPropertyChanged interface like this:
public class TimeAttendance : INotifyPropertyChanged
{
...
double totalHours;
public double TotalHours {
set
{
if (totalHours != value)
{
totalHours = value;
OnPropertyChanged("TotalHours");
}
}
get
{
return totalHours;
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}