Why can't I update the bindings in my Dictionary?

[kyuranger]

What I want to do is to implement a function that dynamically switches the software language without restarting the software or using DynamicResource (because DynamicResource has relatively low performance).

So I plan to achieve this by binding a Dictionary and then dynamically changing the values ​​in the Dictionary.

I first made an ObservableDictionary:

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace AvaloniaApplication1
{

    public class ObservableDictionary<TKey, TValue> : INotifyPropertyChanged
    {
        private readonly Dictionary<TKey, TValue> _dictionary = new();

        public event PropertyChangedEventHandler PropertyChanged;

        public TValue this[TKey key]
        {
            get => _dictionary.TryGetValue(key, out var value) ? value : default;
            set
            {
                _dictionary[key] = value;
                OnPropertyChanged($"Item[{key}]"); 
            }
        }

        public void Add(TKey key, TValue value)
        {
            _dictionary.Add(key, value);
            OnPropertyChanged($"Item[{key}]");
        }

        public bool Remove(TKey key)
        {
            if (_dictionary.Remove(key))
            {
                OnPropertyChanged($"Item[{key}]");
                return true;
            }
            return false;
        }

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

In order to facilitate use in XAML, I wrote a MarkupExtension:

using Avalonia;
using Avalonia.Data;
using Avalonia.Markup;
using Avalonia.Markup.Xaml;
using System;

namespace AvaloniaApplication1
{
   

    public class DictionaryBindingExtension : MarkupExtension
    {
        string key;
        public DictionaryBindingExtension(string key)
        {
            this.key = key;
        }

        public override object ProvideValue(IServiceProvider serviceProvider)
        {
                     
            var binding = new Binding
            {
                Source = MainViewModel.Instance.Data,
                Path = $"[{key}]",
                Mode = BindingMode.OneWay 
            };

            return binding;
        }
    }
}

This is the ViewModel:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace AvaloniaApplication1
{
    public class MainViewModel : INotifyPropertyChanged
    {
        public static MainViewModel Instance { get; } = new MainViewModel();
        private readonly ObservableDictionary<string, string> _data = new();

        public MainViewModel()
        {
            _data.Add("Name", "Initial Value");
            _data.Add("Title", "Hello Avalonia");
        }        
        public ObservableDictionary<string, string> Data => _data;

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

And finally this is the XAML:

<Window xmlns="https://github.com/avaloniaui"
        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"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaApplication1.MainWindow"
		xmlns:local="clr-namespace:AvaloniaApplication1"
		x:DataType="local:MainViewModel"
        Title="AvaloniaApplication1">
	<StackPanel>
		<TextBox Text="{local:DictionaryBinding Name}" />
		<TextBox Text="{local:DictionaryBinding Title}" />
		<Button Content="Update Name" Click="OnUpdateNameClick" />
	</StackPanel>
</Window>

Here is the code for the XAML backend:

using Avalonia.Controls;
using Avalonia.Interactivity;

namespace AvaloniaApplication1
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = MainViewModel.Instance;
        }
        private void OnUpdateNameClick(object sender, RoutedEventArgs e)
        {            
            MainViewModel.Instance.Data["Name"] = "Updated Value";             
        }
    }
}

To facilitate your testing, I packaged and uploaded the entire project:
AvaloniaApplication1.zip

After the program starts, the default bound data will be displayed normally. However, when I click the button to try to change the bound data content, the UI still displays the original data. What is the reason?

[tobyfirth]

You need to use 'Item' as the argument OnPropertyChanged. That is the name of the property. The indexer, '[key]', is not part of the property name.

[kyuranger]

I'm not sure if I understand your meaning correctly. I tried changing OnPropertyChanged($"Item[{key}]"); to OnPropertyChanged($"[{key}]"); but the problem still exists.

[tobyfirth]

It should be OnPropertyChanged("Item"). 'Item' is the name of the property.

[kyuranger]

Well, it works now! Thank you.