Databinding not refreshed in Xamarin (WPF) - wpf

Question

I have some trouble with the data binding while using MVVM in Xamarin. Let me explain my architecture:
I have a Manager-class, which contains a ObservableCollection with classes of type t, t is my model class. The Manager-class contains also a attribute called activeT, which is the current selected object of my model class. There are 2 UIs, one which shows the current data of t. The viewModel is bound to the attribute t of my Manager-class like that:
public t CurrentT
{
get
{
return _mgr.CurrentT;
}
set
{
_mgr.CurrentT = value;
OnPropertyChanged();
}
}
_mgr is my singleton Manager-Object.
Now there is the other view, which is able to choose the current t out of a combobox. The viewModel of that view is bound to the ObservableCollection of the manager. If I change the selected object, I do it like with the same code like above. The Property of the manager is the following code:
public t CurrentT
{
get
{
return _currentT;
}
set
{
_currentT= value;
OnPropertyChanged());
}
}
The problem is now, that the first view to view the current selected t does not refresh, though I can see in the debugger, that the current t is changed by the other view.
Can someone help me?
Edit:
I provide some more Code:
The Manager-Class:
public class Manager : INotifyPropertyChanged
{
private t _currentConstructionSite;
private ObservableCollection<t> _constructionSites = null;
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string name)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(name));
}
public t CurrentConstructionSite
{
get
{
return _currentConstructionSite;
}
set
{
_currentConstructionSite = value;
OnPropertyChanged("CurrentConstructionSite");
}
}
public ObservableCollection<t> ConstructionSites
{
get
{
return _constructionSites;
}
set
{
_constructionSites = value;
}
}
private Manager()
{
ConstructionSites = DataRepository.GenConstructionSites();
_currentConstructionSite = ConstructionSites[0];
}
}
The ViewModels Class A (This is the viewmodel of the view, which shows some data):
public class DashboardViewModel : ViewModelBase
{
private Manager _mgr;
public t CurrentConstructionSite
{
get
{
return _mgr.CurrentConstructionSite;
}
set
{
_mgr.CurrentConstructionSite = value;
OnPropertyChanged();
}
}
public DashboardViewModel()
{
_mgr = Manager.getInstance();
}
}
The View A to show some data:
Binding Setup from XAML:
<ContentPage.BindingContext>
<local:DashboardViewModel x:Name="viewModel"/>
</ContentPage.BindingContext>
Binding a Label to show data:
<Label Text="{Binding CurrentConstructionSite.ConstructionSiteName, Mode=TwoWay}" HorizontalOptions="Center" Font="Bold" FontSize="Large"/>
ViewModel B to choose the current t:
public class ChooseConstructionSiteViewModel : ViewModelBase
{
Manager _mgr = null;
public ObservableCollection<t> ConstructionSites
{
get
{
return _mgr.ConstructionSites;
}
}
public t CurrentConstructionSite
{
get
{
return _mgr.CurrentConstructionSite;
}
set
{
_mgr.CurrentConstructionSite = value;
OnPropertyChanged();
}
}
public ChooseConstructionSiteViewModel()
{
_mgr = Manager.getInstance();
}
}
The View to choose the current t:
<combobox:SfComboBox x:Name="combobox" Grid.Row="0" Grid.Column="1" Margin="8,0,20,0" VerticalOptions="Center" HeightRequest="40" DataSource="{Binding ConstructionSites}" DisplayMemberPath="ConstructionSiteName" SelectionChanged="Handle_SelectionChanged"/>
And if the selection from the combobox changed:
void Handle_SelectionChanged(object sender, Syncfusion.XForms.ComboBox.SelectionChangedEventArgs e)
{
t selectedItem = e.Value as t;
_viewModel.CurrentConstructionSite = selectedItem;
}
The two views are contained as contetPages in a tabbedPage. It works in general, but the changing the selected t in the view B does not update the data in view A. I can see in the debugger that the value of t is changed via view B but when I go back to view A there is the old value. In the debugger I can see that the value is updated.
BTW: ViewModelBase is the class which implements INotifyPropertyChanged

Answer 1

From you second viewmodel, you need to "notify" the first viewmodel that the data has changed.
One of the ways to do that, would be to use a Messenger (MvvmLight has one, so does MvvmCross). You can then use the messenger from your Manager, to notify all the viewmodels that need the info, that CurrentT changed.
In the messenger subscription in your viewmodels, simply call a RaiseNotifyPropertyChanged of your property, and you should be good to go