Question

Setup

• C# WinForms Application.

Summary

• Binding a dictionary to a datagridview.
• Updating the dictionary automatically updates the datagrid.
• The datagrid does not lose focus when the update happens.
• The binding works both ways (editing values in the grid updates the dictionary.

Scenario

• I have a class that calculates values
  based on data from a database.
• The data in this database constantly changes so hence, the calculated values change too.
• These calculated values are added to the properties of a custom object "MyCustomObject".
• Each "MyCustomObject" is then added to a dictionary (or the custom object is updated if it already exists).
• The Dictionary is bound to a datagrid.

The idea

• The idea is that the calculated vales continually change and thus update the dictionary which in turn updates the datagrid.
• Users who are interacting with the datagrid need to be able to see these changes automatically.
• It is imperative that the currently selected row in the datagrid does not lose focus when the grid is updated with the new custom object values.
• The binding must work both ways (editing values in the grid updates the dictionary too.

Question

• How can I implement this automatic binding so that I get the requirements that I need?
• I have already written the code to do all of the calculations and add/update the dictionary of MyCustomObjects.
• Examples of how to implement this datagrid binding would be greatly appreciated.

Answer 1

In order to accomplish this, your Dictionary would need to implement IBindingList and fire the ListChanged event whenever changes were made. Here’s a sample (very) barebones implementation of IDictionary<TKey, TValue> that also implements IBindingList:

public class BindableDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IBindingList
{
    private Dictionary<TKey, TValue> source = new Dictionary<TKey, TValue>();

    void IBindingList.AddIndex(PropertyDescriptor property) { }
    object IBindingList.AddNew() { throw new NotImplementedException(); }
    bool IBindingList.AllowEdit { get { return false; } }
    bool IBindingList.AllowNew { get { return false; } }
    bool IBindingList.AllowRemove { get { return false; } }
    void IBindingList.ApplySort(PropertyDescriptor property, ListSortDirection direction) { }
    int IBindingList.Find(PropertyDescriptor property, object key) { throw new NotImplementedException(); }
    bool IBindingList.IsSorted { get { return false; } }
    void IBindingList.RemoveIndex(PropertyDescriptor property) { }
    void IBindingList.RemoveSort() { }
    ListSortDirection IBindingList.SortDirection { get { return ListSortDirection.Ascending; } }
    PropertyDescriptor IBindingList.SortProperty { get { return null; } }
    bool IBindingList.SupportsChangeNotification { get { return true; } }
    bool IBindingList.SupportsSearching { get { return false; } }
    bool IBindingList.SupportsSorting { get { return false; } }
    int System.Collections.IList.Add(object value) { throw new NotImplementedException(); }
    void System.Collections.IList.Clear() { Clear(); }
    bool System.Collections.IList.Contains(object value) { if (value is TKey) { return source.ContainsKey((TKey)value); } else if (value is TValue) { return source.ContainsValue((TValue)value); } return false; }
    int System.Collections.IList.IndexOf(object value) { return -1; }
    void System.Collections.IList.Insert(int index, object value) { throw new NotImplementedException(); }
    bool System.Collections.IList.IsFixedSize { get { return false; } }
    bool System.Collections.IList.IsReadOnly { get { return true; } }
    void System.Collections.IList.Remove(object value) { if (value is TKey) { Remove((TKey)value); } }
    void System.Collections.IList.RemoveAt(int index) { throw new NotImplementedException(); }
    object System.Collections.IList.this[int index] { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } }

    private ListChangedEventHandler listChanged;

    event ListChangedEventHandler IBindingList.ListChanged
    {
        add { listChanged += value; }
        remove { listChanged -= value; }
    }

    protected virtual void OnListChanged(ListChangedEventArgs e)
    {
        var evt = listChanged;

        if (evt != null) evt(this, e);
    }

    public void Add(TKey key, TValue value)
    {
        source.Add(key, value);

        OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));
    }

    public bool Remove(TKey key)
    {
        if (source.Remove(key))
        {
            OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));

            return true;
        }

        return false;
    }

    public TValue this[TKey key]
    {
        get
        {
            return source[key];
        }
        set
        {
            source[key] = value;

            OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));
        }
    }

    void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item)
    {
        ((ICollection<KeyValuePair<TKey, TValue>>)source).Add(item);

        OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));
    }

    bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
    {
        if (((ICollection<KeyValuePair<TKey, TValue>>)source).Remove(item))
        {
            OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));

            return true;
        }

        return false;
    }

    public bool ContainsKey(TKey key) { return source.ContainsKey(key); }
    public ICollection<TKey> Keys { get { return source.Keys; } }
    public bool TryGetValue(TKey key, out TValue value) { return source.TryGetValue(key, out value); }
    public ICollection<TValue> Values { get { return source.Values; } }
    public void Clear() { source.Clear(); }
    bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item) { return ((ICollection<KeyValuePair<TKey, TValue>>)source).Contains(item); }
    void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) { ((ICollection<KeyValuePair<TKey, TValue>>)source).CopyTo(array, arrayIndex); }
    public int Count { get { return source.Count; } }
    bool ICollection<KeyValuePair<TKey, TValue>>.IsReadOnly { get { return ((ICollection<KeyValuePair<TKey, TValue>>)source).IsReadOnly; } }
    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() { return source.GetEnumerator(); }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { return GetEnumerator(); }
    bool ICollection.IsSynchronized { get { return false; } }
    object ICollection.SyncRoot { get { return null; } }
    void ICollection.CopyTo(Array array, int arrayIndex) { ((ICollection)source).CopyTo(array,arrayIndex); }
}

Unfortunately, the selected row may or may not change, depending on which grid you’re using. Your best bet is to save off the key of the selected row whenever it changes, then reselect that row (if present) when the dictionary is updated. Otherwise, there’s no way to guarantee that you’ll maintain the selection.