Why twoway binding doen't work as expected?

Question

I need some help with binding. Twoway mode doesn't work at all. I fill my window with data passed to the constructor and it's working fine. The problem is that I can't rewrite some data imputed in the window control even if I use Twoway binding. Below is how I open window

    var tempInregistrare = BaseConnection.GetInregistrareById(itemSelected.InregistrareId.ToString());
                var tichet = new TichetView(new InregistrareModel { 
                    Id =tempInregistrare.Id,
                    NumeFurnizor = tempInregistrare.NumeFurnizor,
                    IdFurnizor = tempInregistrare.IdFurnizor,
                    NumeProdus = tempInregistrare.NumeProdus......
ticket.Show();

Here is window constructor with DataContext set to self.

  public TichetView(InregistrareModel inregistrare)
  {
            InitializeComponent();
            InregistrareModel = inregistrare;
            DataContext = this;
            grdButtonsPrint.Visibility = Visibility.Visible;
   }

  public InregistrareModel InregistrareModel
        {
            get => inregistrareModel;
            set
            {
                if (value != inregistrareModel)
                {
                    inregistrareModel = value;
                    NotifyPropertyChanged();
                }
            }
        }
 public class InregistrareModel
    {
        public int Id { get; set; }
        public int IdProdus { get; set; }
        public int IdFurnizor { get; set; }
        public string NumeProdus { get; set; }
        public string NumeFurnizor { get; set; }
        public string NrAuto { get; set; }
        public string NumeSofer { get; set; }
        public double CantitateInitiala { get; set; }
        public double CantitateIesire { get; set; }
        public double Umiditate { get; set; }
        public double CantitateScazuta { get; set; }
        public double CantitateMarfa { get; set; }
        public DateTime DataIntrare { get; set; }
        public DateTime DataIesire { get; set; }
        public FurnizorModel Furnizor { get; set; }
        public int NIR { get; set; }
    }

And here is Xaml of window

                <TextBlock Grid.Row="2" Grid.Column="2" VerticalAlignment="Center">Intrare</TextBlock>                
                <TextBox Grid.Row="2" Grid.Column="3" Text="{Binding InregistrareModel.CantitateInitiala}"/>
   
                
                <TextBlock Grid.Row="4" Grid.Column="2" VerticalAlignment="Center">Umiditatea (%)</TextBlock>
                <TextBox x:Name="txtUmiditate" Grid.Row="4" Grid.Column="3" IsReadOnly="False" Text="{Binding InregistrareModel.Umiditate, Mode=TwoWay}"/>   
                
                <TextBlock Grid.Row="5" Grid.Column="2" VerticalAlignment="Center">Cantitatea scazuta</TextBlock>
                <TextBox x:Name="txtCantitateScazuta" Grid.Row="5" Grid.Column="3" IsReadOnly="False" Text="{Binding InregistrareModel.CantitateScazuta, Mode=TwoWay}"/>
                
                <TextBlock Grid.Row="6" Grid.Column="2" VerticalAlignment="Center">Iesire</TextBlock>
                <TextBox Grid.Row="6" Grid.Column="3" Text="{Binding InregistrareModel.CantitateIesire}"/>
                
                <TextBlock Grid.Row="7" Grid.Column="2" VerticalAlignment="Center">Dată iesire</TextBlock>
                <TextBox Grid.Row="7" Grid.Column="3" Text="{Binding InregistrareModel.DataIesire,StringFormat='{}{0:HH:HH dd/M/yyyy}'}"/>
                
                <TextBlock Grid.Row="10" Grid.Column="2" VerticalAlignment="Center">Net</TextBlock>
                <TextBox Grid.Row="10" Grid.Column="3" Text="{Binding InregistrareModel.CantitateMarfa}"/>

All text boxes are filled with data expect the second and third that I fill by hand. The goal that I can't achieve right now is to take data from 1st textbox(InregistrareModel.CantitateInitiala) to type in 3rd(txtCantitateScazuta) some data and show the result in the last textbox so after I update my database with this data.

What does `InregistrareModel` look like? You need to make the properties of `InregistrareModel` observable. — Peter Boone, Sep 29 '20 at 14:18
InregistrareModel needs to implement INotifyPropertyChanged to let the Binding work properly. — trix, Sep 29 '20 at 14:30
Remove whatever code is creating something that creates itself. Which you've not shown us. — Andy, Sep 29 '20 at 15:25
`TextBox.Text` binds `TwoWay` by default. As trix suggested, implement `INotifyPropertyChanged`. Every object that is the source of a `Binding` must implement this interface or implement its properties as `DependencyProperty` no matter the `Binding.Mode`. Then show the line of code that throws the exception. — BionicCode, Sep 29 '20 at 15:27

score 0 · Answer 1 · answered Sep 29 '20 at 15:48

You should make the ViewModel a separate file/class. Let's call it TichetViewModel. This class should have the InregistrareModel. Something like this:

public class TichetViewModel : ObservableObject
{
    private InregistrareModel _InregistrareModel;
    public InregistrareModel InregistrareModel
    {
        get { return _InregistrareModel; }
        set
        {
            if (value != _InregistrareModel)
            {
                _InregistrareModel = value;
                NotifyPropertyChanged();
            }
        }
    }

    public TichetViewModel()
    {
        InregistrareModel = new InregistrareModel();
    }
}

Then set the DataContext of TichetView in either you code behind or in xaml.

Code behind:

TichetView.xaml.cs

public TichetView()
{
    InitializeComponent();
    DataContext = new TichetViewModel();
}

or in xaml

TichetView.xaml

<Window.DataContext>
    <local:TichetViewModel />
</Window.DataContext>

I like doing this in xaml because the Intellisense in Visual Studio picks this up and autocompletes based on the classes.

Implement INotifyPropertyChanged on the properties of the InregistrareModel. Like this:

public class InregistrareModel : ObservableObject
{
    private int _Id;
    public int Id
    {
        get { return _Id; }
        set
        {
            if (value != _Id)
            {
                _Id = value;
                NotifyPropertyChanged();
            }
        }
    }

    private string _NumeProdus;
    public string NumeProdus
    {
        get { return _NumeProdus; }
        set
        {
            if (value != _NumeProdus)
            {
                _NumeProdus = value;
                NotifyPropertyChanged();
            }
        }
    }
}

EldHasp · Accepted Answer · 2020-09-30T18:00:54.900

I totally agree with @Peter Boone. You have a lot of gross architectural mistakes in the Solution and for good reason it needs to be completely redone. But if you do not have such an opportunity, try to implement this option.

For fields (TextBox, TextBlock) that change, declare properties in the Window. In the body of these properties, implement communication with the parent container (InregistrareModel) and with other properties.

Let's say you have a CantitateInitiala property that affects the value of the CantitateScazuta property.

    public InregistrareModel InregistrareModel
    {
        get => inregistrareModel;
        set
        {
            if (value != inregistrareModel)
            {
                inregistrareModel = value;
                NotifyPropertyChanged();
                CantitateInitiala = InregistrareModel.CantitateInitiala;
            }
        }

    public double CantitateInitiala
    {
        get => InregistrareModel.CantitateInitiala;
        set
        {
            if (value != InregistrareModel.CantitateInitiala)
            {
                InregistrareModel.CantitateInitiala = value;
                NotifyPropertyChanged();

                // Calculation of the CantitateScazuta value
                double cantSc = CantitateInitiala / 123.45;

                CantitateScazuta = cantSc;
            }
        }
    }
    public double CantitateScazuta
    {
        get => InregistrareModel.CantitateScazuta;
        set
        {
            if (value != InregistrareModel.CantitateScazuta)
            {
                InregistrareModel.CantitateScazuta = value;
                NotifyPropertyChanged();
            }
        }
    }

In XAML, change the bindings for these fields:

            <TextBlock Grid.Row="2" Grid.Column="2" VerticalAlignment="Center">Intrare</TextBlock>                
            <TextBox Grid.Row="2" Grid.Column="3" Text="{Binding CantitateInitiala}"/>

            
            <TextBlock Grid.Row="4" Grid.Column="2" VerticalAlignment="Center">Umiditatea (%)</TextBlock>
            <TextBox x:Name="txtUmiditate" Grid.Row="4" Grid.Column="3" IsReadOnly="False" Text="{Binding InregistrareModel.Umiditate, Mode=TwoWay}"/>   
            
            <TextBlock Grid.Row="5" Grid.Column="2" VerticalAlignment="Center">Cantitatea scazuta</TextBlock>
            <TextBox x:Name="txtCantitateScazuta" Grid.Row="5" Grid.Column="3" IsReadOnly="False" Text="{Binding CantitateScazuta, Mode=TwoWay}"/>

Но нужно тщательно продумать алгоритм зависимостей свойств в том случае, если они имеют циклическую зависимость. То есть не только изменение CantitateInitiala влияет на значение CantitateScazuta, но также существует обратная зависимость CantitateInitiala от изменения CantitateScazuta.

Why twoway binding doen't work as expected?

2 Answers2