Is it possible to bind to an indexed property in xaml using the same property path syntax as a standard property?

Question

In XAML (specifically on Universal Windows Platform) I can data bind to an indexed property using the property path notation for indexers.

e.g. Given a data source of type Dictionary<string,string> I can bind to an indexed property as follows:

<TextBlock Text="{Binding Dictionary[Property]}"/>

In the above, the TextBlock's DataContext is set to an object with a dictionary property, say the following:

public class DataObject
{
    public Dictionary<string,string> Dictionary { get; } = new Dictionary<string,string> {["Property"]="Value"};
}

My question is, is it possible to bind to the indexed property without using the indexer notation, but instead using the syntax for standard property binding?

i.e.

<TextBlock Text="{Binding Dictionary.Property}"/>

From my initial tests this doesn't seem to work. Is there an easy way to make it work? I want to use a data source object with an indexed property (like the Dictionary in this case but could just be a simple object). I don't want to use dynamic objects.

Answer 1

There is no syntax that does what you want, I'm afraid. The syntax for standard property binding works for standard properties, e.g.,

<TextBlock Text="{Binding Dictionary.Count}" />

...will bind to the Count property of the dictionary (or whatever object). You need them brackets...

EDIT

If you really hate the brackets, the closest thing I can find would be to use a converter with a parameter. For example:

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        IDictionary<string, string> dictionary = value as IDictionary<string, string>;
        string dictionaryValue;
        if (dictionary != null && dictionary.TryGetValue(parameter as string, out dictionaryValue))
        {
            return dictionaryValue;
        }

        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotSupportedException();
    }
}

XAML:

<Page
    x:Class="UWP.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:uwp="using:UWP">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.Resources>
            <uwp:MyConverter x:Key="MyConverter" />
        </Grid.Resources>
        <Grid.DataContext>
            <uwp:DataObject />
        </Grid.DataContext>
        <TextBlock
            Text="{Binding Dictionary, ConverterParameter=Property1, Converter={StaticResource MyConverter}}" />
    </Grid>
</Page>

...which is a roundabout way of ending up with something harder to read than the brackets.

Answer 2

A long time ago there was this ObservableDictionary class in Windows 8 app templates that does what you want. It's not a Dictionary<string, string>, but you can copy values from your Dictionary into the ObservableDictionary

Usage

Declare an ObservableDictionary property in your ViewModel, then bind to its indexer like usual properties:

using System;
using System.Collections.Generic;
using System.Linq;
using Windows.Foundation.Collections;

namespace MyApp
{
    public class ObservableDictionary : IObservableMap<string, object>
    {
        private class ObservableDictionaryChangedEventArgs : IMapChangedEventArgs<string>
        {
            public ObservableDictionaryChangedEventArgs(CollectionChange change, string key)
            {
                this.CollectionChange = change;
                this.Key = key;
            }

            public CollectionChange CollectionChange { get; private set; }
            public string Key { get; private set; }
        }

        private Dictionary<string, object> _dictionary = new Dictionary<string, object>();
        public event MapChangedEventHandler<string, object> MapChanged;

        private void InvokeMapChanged(CollectionChange change, string key)
        {
            var eventHandler = MapChanged;
            if (eventHandler != null)
            {
                eventHandler(this, new ObservableDictionaryChangedEventArgs(change, key));
            }
        }

        public void Add(string key, object value)
        {
            this._dictionary.Add(key, value);
            this.InvokeMapChanged(CollectionChange.ItemInserted, key);
        }

        public void Add(KeyValuePair<string, object> item)
        {
            this.Add(item.Key, item.Value);
        }

        public bool Remove(string key)
        {
            if (this._dictionary.Remove(key))
            {
                this.InvokeMapChanged(CollectionChange.ItemRemoved, key);
                return true;
            }
            return false;
        }

        public bool Remove(KeyValuePair<string, object> item)
        {
            object currentValue;
            if (this._dictionary.TryGetValue(item.Key, out currentValue) &&
                Object.Equals(item.Value, currentValue) && this._dictionary.Remove(item.Key))
            {
                this.InvokeMapChanged(CollectionChange.ItemRemoved, item.Key);
                return true;
            }
            return false;
        }

        public virtual object this[string key]
        {
            get
            {
                return this._dictionary[key];
            }
            set
            {
                this._dictionary[key] = value;
                this.InvokeMapChanged(CollectionChange.ItemChanged, key);
            }
        }

        public void Clear()
        {
            var priorKeys = this._dictionary.Keys.ToArray();
            this._dictionary.Clear();
            foreach (var key in priorKeys)
            {
                this.InvokeMapChanged(CollectionChange.ItemRemoved, key);
            }
        }

        public ICollection<string> Keys
        {
            get { return this._dictionary.Keys; }
        }

        public bool ContainsKey(string key)
        {
            return this._dictionary.ContainsKey(key);
        }

        public bool TryGetValue(string key, out object value)
        {
            return this._dictionary.TryGetValue(key, out value);
        }

        public ICollection<object> Values
        {
            get { return this._dictionary.Values; }
        }

        public bool Contains(KeyValuePair<string, object> item)
        {
            return this._dictionary.Contains(item);
        }

        public int Count
        {
            get { return this._dictionary.Count; }
        }

        public bool IsReadOnly
        {
            get { return false; }
        }

        public IEnumerator<KeyValuePair<string, object>> GetEnumerator()
        {
            return this._dictionary.GetEnumerator();
        }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return this._dictionary.GetEnumerator();
        }

        public void CopyTo(KeyValuePair<string, object>[] array, int arrayIndex)
        {
            int arraySize = array.Length;
            foreach (var pair in this._dictionary)
            {
                if (arrayIndex >= arraySize) break;
                array[arrayIndex++] = pair;
            }
        }
    }
}

Answer 3

class DictionaryXamlWrapper : DynamicObject, INotifyPropertyChanged
{
    #region PropertyChangedFunctional
    public void OnPropertyChanged([CallerMemberName] string aProp = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(aProp));
    }

    public event PropertyChangedEventHandler PropertyChanged;
    #endregion

    Dictionary<string, object> members = new Dictionary<string, object>();

    // установка свойства
    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        members[binder.Name] = value;
        OnPropertyChanged(binder.Name);
        return true;
    }
    // получение свойства
    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        result = null;
        if (members.ContainsKey(binder.Name))
        {
            result = members[binder.Name];
            return true;
        }

        return false;
    }
}

Of course, you can delete INotifyPropertyChanged functional if you do not need it.

And usage as you wanted

<TextBlock Text="{Binding DictionaryXamlWrapper.TestField}"/>