I am trying to bind the Microsoft sample ObservableConcurrentDictionary.cs object to a TreeView. I have searched for examples on binding a Dictionary but although there are many examples, none of them seem to work for me. Whenever I run it the screen shows up with an empty treeview (only white outline). I have stripped down my code to the bare minimum to test and my implementation is as follows:
<Window x:Name="AppWindow" x:Class="ControlCenter.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Control Center" Height="1000" Width="1200"
WindowStartupLocation="CenterScreen">
<Grid x:Name="left_grid" Margin="362,199,551,237">
<TreeView ItemsSource="{Binding _hostList}">
<TreeView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding _hostList.Values}"/>
</DataTemplate>
</TreeView.ItemTemplate>
</TreeView>
</Grid>
public partial class MainWindow : Window
{
public ObservableConcurrentDictionary<string, string> _hostList = new ObservableConcurrentDictionary<string, string>();
public MainWindow()
{
InitializeComponent();
_hostList.Add("TestHost1", "Host1");
_hostList.Add("TestHost2", "Host2");
_hostList.Add("TestHost3", "Host3");
}
}
using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Threading;
using System.Diagnostics;
namespace System.Collections.Concurrent
{
[DebuggerDisplay("Count={Count}")]
public class ObservableConcurrentDictionary<TKey, TValue> :
ICollection<KeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue>,
INotifyCollectionChanged, INotifyPropertyChanged
{
private readonly SynchronizationContext _context;
private readonly ConcurrentDictionary<TKey, TValue> _dictionary;
/// <summary>
/// Initializes an instance of the ObservableConcurrentDictionary class.
/// </summary>
public ObservableConcurrentDictionary()
{
_context = AsyncOperationManager.SynchronizationContext;
_dictionary = new ConcurrentDictionary<TKey, TValue>();
}
/// <summary>Event raised when the collection changes.</summary>
public event NotifyCollectionChangedEventHandler CollectionChanged;
/// <summary>Event raised when a property on the collection changes.</summary>
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Notifies observers of CollectionChanged or PropertyChanged of an update to the dictionary.
/// </summary>
private void NotifyObserversOfChange()
{
var collectionHandler = CollectionChanged;
var propertyHandler = PropertyChanged;
if (collectionHandler != null || propertyHandler != null)
{
_context.Post(s =>
{
if (collectionHandler != null)
{
collectionHandler(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
if (propertyHandler != null)
{
propertyHandler(this, new PropertyChangedEventArgs("Count"));
propertyHandler(this, new PropertyChangedEventArgs("Keys"));
propertyHandler(this, new PropertyChangedEventArgs("Values"));
}
}, null);
}
}
/// <summary>Attempts to add an item to the dictionary, notifying observers of any changes.</summary>
/// <param name="item">The item to be added.</param>
/// <returns>Whether the add was successful.</returns>
private bool TryAddWithNotification(KeyValuePair<TKey, TValue> item)
{
return TryAddWithNotification(item.Key, item.Value);
}
/// <summary>Attempts to add an item to the dictionary, notifying observers of any changes.</summary>
/// <param name="key">The key of the item to be added.</param>
/// <param name="value">The value of the item to be added.</param>
/// <returns>Whether the add was successful.</returns>
private bool TryAddWithNotification(TKey key, TValue value)
{
bool result = _dictionary.TryAdd(key, value);
if (result) NotifyObserversOfChange();
return result;
}
/// <summary>Attempts to remove an item from the dictionary, notifying observers of any changes.</summary>
/// <param name="key">The key of the item to be removed.</param>
/// <param name="value">The value of the item removed.</param>
/// <returns>Whether the removal was successful.</returns>
private bool TryRemoveWithNotification(TKey key, out TValue value)
{
bool result = _dictionary.TryRemove(key, out value);
if (result) NotifyObserversOfChange();
return result;
}
/// <summary>Attempts to add or update an item in the dictionary, notifying observers of any changes.</summary>
/// <param name="key">The key of the item to be updated.</param>
/// <param name="value">The new value to set for the item.</param>
/// <returns>Whether the update was successful.</returns>
private void UpdateWithNotification(TKey key, TValue value)
{
_dictionary[key] = value;
NotifyObserversOfChange();
}
#region ICollection<KeyValuePair<TKey,TValue>> Members
void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item)
{
TryAddWithNotification(item);
}
void ICollection<KeyValuePair<TKey, TValue>>.Clear()
{
((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).Clear();
NotifyObserversOfChange();
}
bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item)
{
return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).Contains(item);
}
void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).CopyTo(array, arrayIndex);
}
int ICollection<KeyValuePair<TKey, TValue>>.Count
{
get { return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).Count; }
}
bool ICollection<KeyValuePair<TKey, TValue>>.IsReadOnly
{
get { return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).IsReadOnly; }
}
bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
{
TValue temp;
return TryRemoveWithNotification(item.Key, out temp);
}
#endregion
#region IEnumerable<KeyValuePair<TKey,TValue>> Members
IEnumerator<KeyValuePair<TKey, TValue>> IEnumerable<KeyValuePair<TKey, TValue>>.GetEnumerator()
{
return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return ((ICollection<KeyValuePair<TKey, TValue>>)_dictionary).GetEnumerator();
}
#endregion
#region IDictionary<TKey,TValue> Members
public void Add(TKey key, TValue value)
{
TryAddWithNotification(key, value);
}
public bool ContainsKey(TKey key)
{
return _dictionary.ContainsKey(key);
}
public ICollection<TKey> Keys
{
get { return _dictionary.Keys; }
}
public bool Remove(TKey key)
{
TValue temp;
return TryRemoveWithNotification(key, out temp);
}
public bool TryGetValue(TKey key, out TValue value)
{
return _dictionary.TryGetValue(key, out value);
}
public ICollection<TValue> Values
{
get { return _dictionary.Values; }
}
public TValue this[TKey key]
{
get { return _dictionary[key]; }
set { UpdateWithNotification(key, value); }
}
#endregion
}
}
There are a few problems. First since you didn't specify a source in your binding it is going off of the DataContext which is null.
I think you are thinking that since you are working with MainWindow that the source of your binding statements will be the MainWindow object but that isn't the default for a binding. If you wanted to do that you would have to use a RelativeSource in your bindings, but usually you would just pop the collection into the DataContext as part of a view model or directly as the entire view model instead. Something like this:
public ObservableConcurrentDictionary<string, string> _hostList = new ObservableConcurrentDictionary<string, string>();
public MainWindow()
{
InitializeComponent();
_hostList.Add("TestHost1", "Host1");
_hostList.Add("TestHost2", "Host2");
_hostList.Add("TestHost3", "Host3");
DataContext = _hostList;
}
Then you will just have your bindings go off of the DataContext so you would update your code as follows:
<TreeView ItemsSource="{Binding}">
<TreeView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Values}"/>
</DataTemplate>
</TreeView.ItemTemplate>
</TreeView>
This won't completely resolve your problems I am thinking though since I think you are binding to the wrong properties. ItemsSource should be binding to something that is an IEnumerable of some sort and Text should be binding to a string.
So I am not sure what you are ideally trying to show but am pretty sure you aren't binding correctly. Usually with a TreeView you will be using a HierarchicalDataTemplate and I think this is likely what you are wanting to use.