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MVVM/WPF UI not update when executing method second time

I'm having troubles with my UI not updating when my properties change, even though I have INotifyPropertyChange applied. When i run the code the first time, it shows up correct and the UI is updated. While debbuging I can see the new values being set to the strings of the viewmodel and that the OnPropertChange event is fired, it just don't happen anything in the UI. The code below will be in order of events. As extra information, I use the same code to update the viewmodel both in the first and second time.
public partial class Transaktioner : Window
{
ViewModelCommon.ViewModel view = new ViewModelCommon.ViewModel();
private static List<ViewModelCommon.Items2> getAccountingRowsListEdited = new List<ViewModelCommon.Items2>();
{
DataContext = view;
InitializeComponent();
}
private async Task GetAccountinTransactionsAsync()
{
await Task.Run(() =>
{
getAccountingRowsList = client.GetAccountingTransactions(ftglist[index], 0, ref status).ToList();
foreach (var v in getAccountingRowsList)
{
getAccountingRowsListEdited.Add(new ViewModelCommon.Items2
{
itemName2 = v.ver.ToString(),
value2 = v.text,
vertyp = v.vtyp,
s2 = v.kto.ToString(),
s3 = v.trdat.ToString()
});
}
Task.Run(async () =>
{
await SearchAndDisplayResult();
});
});
}
private async Task SearchAndDisplayResult(int exclusion = 0)
{
await Task.Run(() =>
{
var verfikationer = getAccountingRowsListEdited.Where(u => u.vertyp != exclusion).Count(u => u.s2.ToString().Equals("0"));
view.VerifikationerTotal = verfikationer.ToString();
});
}
The ViewModel:
class ViewModelCommon
{
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected bool SetProperty<T>(ref T field, T newValue, [CallerMemberName]string propertyName = null)
{
if (!EqualityComparer<T>.Default.Equals(field, newValue))
{
field = newValue;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
return true;
}
return false;
}
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
protected void Test(string sb)
{
Transaktioner tr = new Transaktioner("");
tr.ExcludeStringChanged(sb);
}
}
public class ViewModel : ViewModelBase
{
private string _verifikationerTotal;
public string VerifikationerTotal
{
get { return _verifikationerTotal; }
set
{
if (value != _verifikationerTotal)
{
_verifikationerTotal = value;
OnPropertyChanged("VerifikationerTotal");
}
}
}
private string _ExcludeString;
public string ExcludeString
{
get { return _ExcludeString; }
set
{
if (value != _ExcludeString)
{
_ExcludeString = value;
OnPropertyChanged("ExcludeString");
Test(ExcludeString);
}
}
}
}
The WPF:
<TextBox x:Name="TextBoxVerifikationerTotal" Text="{Binding VerifikationerTotal}" IsEnabled="False" HorizontalAlignment="Left" Height="23" Margin="583,182,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="99"/>
<TextBox HorizontalAlignment="Left" Height="23" Margin="837,10,0,0" TextWrapping="Wrap" Text="{Binding Path=ExcludeString, Mode=TwoWay, UpdateSourceTrigger=LostFocus}" VerticalAlignment="Top" Width="286"/>
The code above works as expected.
In the UI there is an option to introduce the optional attribute to exclude values. Those are bound to the "ExludeString" this also works and fires the event passing it again to the SearchAndDisplayResult(int exclusion = 0) with the replaces value of the int being passed. While debugging I can see that the event can successfully find a new value and passing it to the ViewModel, but it doesn't update the UI.
Are there any thoughts on why the UI is not updated? Thank you in advance!
The code has been shortend to show the vitals

Answer for this case was the
ViewModelCommon.ViewModel view = new ViewModelCommon.ViewModel();
not being set to a private static while working with Tasks.

Label Text not Updating from ViewModel Xamarin Forms

I am trying to get the text of a label to update on the front of end of my app.
At the moment Im using Message Centre to send a notification up to the view model and increment a number that should update on the label in the view.
Im using Xamarin Forms and PCL.
I can get the number to log out in the debug so I know the message centre is working. But its not updating the view.
the relevant Xaml:
<Label Text="{Binding counter}"
Grid.Row="0"/>
The code behind:
public partial class DriverDashboardView : ContentPage
{
private DriverDashboardViewModel driverdashboardviewmodel;
public DriverDashboardView()
{
InitializeComponent();
this.Title = "Driver's Dashboard";
BindingContext = driverdashboardviewmodel = new DriverDashboardViewModel();
dataList.ItemTapped += DataList_ItemTapped;
}
private void DataList_ItemTapped(object sender, ItemTappedEventArgs e)
{
DisplayAlert("Route Information","Various Data","OK");
}
protected async override void OnAppearing()
{
base.OnAppearing();
await driverdashboardviewmodel.GetLabelInfo();
}
}
The View Model:
public class DriverDashboardViewModel:BaseViewModel,INotifyPropertyChanged
{
private int messageCounter { get; set; }
public string counter { get { return messageCounter.ToString(); }
set {
if (Equals(value, messageCounter)) return;
messageCounter = Convert.ToInt32(value);
OnPropertyChanged(nameof(counter));
} }
public DriverDashboardViewModel()
{
MessagingCenter.Subscribe<App>((App)Application.Current, "Increase", (variable) => {
messageCounter++;
});
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this,
new PropertyChangedEventArgs(propertyName));
}
}
And the relevant section that implements the message centre:
Foregroundmessages.cs:
MessagingCenter.Send((App)Xamarin.Forms.Application.Current, "Increase");
As stated the messaging centre works fine. It gets as far as the view model but doesnt update the counter variable to the view. I have tried setting the counter as an int and a string hence the conversion in the get and set.
I also tried observable collection but that seemed redundant because its a single variable not a collection or list.
Any ideas?

your code is updating the private messageCounter property, not the public counter property that you are binding to. Updating messageCounter does not cause PropertyChanged to fire.
MessagingCenter.Subscribe<App>((App)Application.Current, "Increase", (variable) => {
messageCounter++;
});

Why is my XAML not responding to a change in a variable

there is probably a really simple reason why this isnt working but I've tried everything. I have a TextBlock with Text bound to a variable, the variable changes but the Text doesn't :
<TextBlock x:Name="modeLabel" Style="{StaticResource IndiTextBlock}" Height="23" TextWrapping="Wrap" Grid.Row="0" Text="{Binding ModeLabelText}" Margin="35,22,58,0"/>
The code that controls the text value is in a viewmodel:
public string ModeLabelText { get { return _modeLabeltext; } }
public ComboBoxItem SelectedMode { get { return _selectedMode; }
set
{
if (_selectedMode == value) return;
_selectedMode = value;
ToggleMode(null);
EvaluateScenario(null);
}
and
private void ToggleMode(object parameter)
{
if (_isBasicCalculation)
{
_modeLabeltext = "Target profit";
_isBasicCalculation = false;
}
else
{
_modeLabeltext = "Total to invest";
_isBasicCalculation = true;
}
}

Your class has to implement the INotifyPropertyChanged interface, and on changes of your variables, you should trigger the event
public class Model : INotifyPropertyChanged
{
public event EventHandler PropertyChanged; // event from INotifyPropertyChanged
protected void RaisePropertyChanged(string propertyName)
{
var local = PropertyChanged;
if (local != null)
{
local.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
public void ToggleMode()
{
// ... your code ...
RaisePropertyChanged("ModelLabelText");
}
}

Thank you Nguyen Kien
private void ToggleMode(object parameter)
{
if (_isBasicCalculation)
{
_modeLabeltext = "Target profit";
OnPropertyChanged("ModeLabelText");
_isBasicCalculation = false;
}
else
{
_modeLabeltext = "Total to invest";
OnPropertyChanged("ModeLabelText");
_isBasicCalculation = true;
}
}

Databinding - Listbox doesn't update when updating data after reloading from database

I have a listbox which has items populated from a database. Now I want to update a listbox with a new string value each time I call the Add function.
I did this in 2 ways.
I added the new value to the database and updated the ViewModel class where the listbox is binded to. And this works fine. (see AddNewNameFirstWay method below)
I added the new value to the database, reloaded the values from the database and updated the ViewModel. But this doesn't work. (see AddNewNameSecondWay method below)
Here is my ViewModel code
public class ViewModel
{
private DBContext context = new DBContext("Data source=isostore:/names2.sdf");
private ObservableCollection<NameTable> nameCollection;
public ObservableCollection<NameTable> NameCollection
{
get
{
return nameCollection;
}
set
{
if (nameCollection != value)
{
nameCollection = value;
NotifyPropertyChanged();
}
}
}
public void AddNewNameSecondWay(string s)
{
NameTable t = new NameTable() { Name = s };
context.NameDatabaseTable.InsertOnSubmit(t);
context.SubmitChanges();
LoadFromDB();
}
public void AddNewNameFirstWay(string s)
{
NameTable t = new NameTable() { Name = s };
context.NameDatabaseTable.InsertOnSubmit(t);
context.SubmitChanges();
NameCollection.Add(t);
}
public void LoadFromDB()
{
var query = from i in context.NameDatabaseTable
select i;
NameCollection = new ObservableCollection<NameTable>(query);
}
private void NotifyPropertyChanged([System.Runtime.CompilerServices.CallerMemberName]string propertyName = null)
{
var tmp = PropertyChanged;
if (tmp != null)
tmp(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
}
Here is my XAML binding code
<ListBox ItemsSource="{Binding NameCollection, Mode=OneWay}" >
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name, Mode=OneWay}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
It seems to me that second method doesn't work, because the ObservableCollection memory reference changes. If this is correct, how to update the binding properly?
Reason I use the second method is that, I want to make sure all the DB constraints stands true for the values I insert.

You need to notify about the changes in property. Try this way for Framework 4.0,
Mode=OneWayToSource,UpdateSourceTrigger=PropertyChanged
Hope it helps...

Call OnPropertyChanged when you want notification about changes in your collection:
OnPropertyChanged("NameCollection")
Your ViewModel:
public class ViewModel: INotifyPropertyChanged
{
private DBContext context = new DBContext("Data source=isostore:/names2.sdf");
private ObservableCollection<NameTable> nameCollection;
public ObservableCollection<NameTable> NameCollection
{
get
{
return nameCollection;
}
set
{
if (nameCollection != value)
{
nameCollection = value;
OnPropertyChanged("NameCollection");
}
}
}
public void AddNewNameSecondWay(string s)
{
// your code
OnPropertyChanged("NameCollection");
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}

Updating UI based on property change in a view model

I'm new to WPF, so there's probably something basic I'm missing here. I have an application that looks like this:
<Window x:Class="MyApp.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Test Application" Height="647" Width="723" Background="#88B0FF">
<DockPanel Name="MainDock">
<Button DockPanel.Dock="Top" Margin="5,0,5,0" x:Name="PingButton" Click="PingButton_OnClick">Ping</Button>
<TextBox Text="{Binding Path=Output}" />
</DockPanel>
</Window>
The code-behind is like this:
public partial class MainWindow : Window
{
private Model _applicationModel = new Model();
public Model ApplicationModel {
get { return _applicationModel; }
set { _applicationModel = value; }
}
public MainWindow()
{
InitializeComponent();
this.DataContext = ApplicationModel;
ApplicationModel.Output = "Not clicked";
}
private void PingButton_OnClick(object sender, RoutedEventArgs e)
{
ApplicationModel.Output = "Clicked";
}
}
I have a small class called Model that implements INotifyPropertyChanged.
public class Model : INotifyPropertyChanged
{
public string Output { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}
I run this application, and the text box displays the text "Not clicked". When I click the button, I would expect that the text would change. It does not. The "ApplicationModel" object is updated, and this is reflected in the DataContext; I have a breakpoint in the OnPropertyChanged() method, however, and it appears that it's never being called.
What am I doing wrong?

OnPropertyChanged() isn't being called because you're not calling it.
There is no special magic that wires up calls to OnPropertyChanged by itself, so you need to do it yourself.
Specifically, you should modify your Output property to call it when it changes (and it wouldn't hurt to do the same for your ApplicationModel property:
private string output;
public string Output
{
get { return output; }
set
{
if (output != value)
{
output = value;
OnPropertyChanged("Output");
}
}
}
If you're targeting .NET 4.5 you can utilize the CallerMemberName attribute to reduce boilerplate code; This article explains how to do so. Then you'll have something like this:
private string output;
public string Output
{
get { return output; }
set { SetProperty(ref output, value); }
}
If you're using .NET 4.0 or below, you can use expression trees, as described in this answer.