PropertyChanged isn't working as expected

Question

I'm currently trying myself on creating a WPF project with MVVM using Fody Property changed.

<Window x:Class="TestMVVM.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:TestMVVM"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525"
    DataContext="{x:Static local:MainWindowViewModel.Instance}"
    x:Name="WindowElement">

<StackPanel Orientation="Horizontal">        
    <TextBlock Text="{Binding Text, Mode=TwoWay}" />
    <Button Content="Browse" Command="{Binding WSDLBrowseClick}"/> 
</StackPanel>

public static class Model
{
    public static string text { get; set; }
}

public class MainWindowViewModel : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged = (sender, e) => { }; 

    public static MainWindowViewModel Instance => new MainWindowViewModel();

    public string Text { get; set; }
    /*
    {
        get { return Model.text; }
        set
        {
            if (value == Text)
                return;

            Model.text = value;

            PropertyChanged(this, new PropertyChangedEventArgs("Text"));
        }
    }*/

    public ICommand WSDLBrowseClick { get; set; }


    public MainWindowViewModel()
    {
        WSDLBrowseClick = new RelayCommand(BrowseWSDL);
    }


    private void BrowseWSDL()
    {
        Text = "Test";           
    }
}

Basically I want the TextBlock to show the "Test"-Text when I click the button. The Click-Command gets executed but the TextBlock's text doesn't change. I want to use the property Text as a local memory that keeps the textblock up to date so I can later send the value to model.text and use it there. But it only works if I use the code that I have currently commented out. Isn't fody weaver supposed to do the same thing for me (just that he creates another private variable instead of using model.text)?

Looks correct, did you add the weaver to FodyWeavers.xml? Also try without the empty guard delegate on the PropertyChangedEvent, could be that Fody doesn't want to overwrite that. — Lennart, Nov 10 '17 at 10:13

score 2 · Accepted Answer · answered Nov 13 '17 at 08:23

2

I managed to make it work by adding <PropertyChanged/> to my FodyWeavers.xml

answered Nov 13 '17 at 08:23

Theo

31
5

Thanku you, so much. I was stuck since last 1 day. many many thanks – Colonel Software Sep 17 '19 at 06:03

score 0 · Answer 2 · answered Nov 10 '17 at 10:05

0

From what I can tell from the example you need to mark the class with [ImplementPropertyChanged] attribute.

Source

answered Nov 10 '17 at 10:05

Igor Meszaros

2,081
2
22
46

This attribute is obsolete by now, implementing INotifyPropertyChanged on the class is enough – Lennart Nov 10 '17 at 10:10
If `[ImplementPropertychanged]` is obsolete it's replacement must be `[AddINotifyPropertyChangedInterface]` – PandaWood Jul 27 '21 at 12:50

score -1 · Answer 3 · answered Nov 11 '17 at 04:23

It seems you are not notifying that the text has changed at all, therefore the view has no clue there is a new value!

Try this code (complete with property changed logic for your sanity) in substitute of the Text variable setter:

    public string Text
    {
        get => _text;
        set
        {
            OnPropertyChanged(nameof(Text));
            _text = value;
        }
    }
    private string _text;
    public event PropertyChangedEventHandler PropertyChanged;
    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

PLUS you need to update a section of your XAML to say:

<TextBlock Text="{Binding Text, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

PropertyChanged isn't working as expected

3 Answers3