キャプテンが提案したものと同様のアプローチを使用しました。複数のアイテム (つまり、選択されたすべてのアイテム) を表す ViewModel に 1 つのプロパティを作成しました。プロパティの get- および set-accessors では、次のメソッドを使用して、すべてのアイテムの共有値を決定/設定しました。このアプローチはリフレクションを使用しませんが、ラムダ式の形式でデリゲートを使用するため、かなり高速になります。
概要として、これは私の基本的な設計です。
public class MyMultiSelectionViewModel
{
private List<MyItemType> m_selectedItems = new List<MyItemType>();
public void UpdateSelectedItems(IList<MyItemType> selectedItems)
{
m_selectedItems = selectedItems;
this.OnPropertyChanged(() => this.MyProperty1);
this.OnPropertyChanged(() => this.MyProperty2);
// and so on for all relevant properties
}
// properties using SharedValueHelper (see example below)
}
プロパティは次のようになります。
public string Name
{
get
{
return SharedValueHelper.GetSharedValue<MyItemType, string>(m_selectedItems, (item) => item.Name, String.Empty);
}
set
{
SharedValueHelper.SetSharedValue<MyItemType, string>(m_selectedItems, (item, newValue) => item.Name = newValue, value);
this.OnPropertyChanged(() => this.Name);
}
}
クラスのコードはSharedValueHelper次のようになります。
/// <summary>
/// This static class provides some methods which can be used to
/// retrieve a <i>shared value</i> for a list of items. Shared value
/// means a value which represents a common property value for all
/// items. If all items have the same property value, this value is
/// the shared value. If they do not, a specified <i>non-shared value</i>
/// is used.
/// </summary>
public static class SharedValueHelper
{
#region Methods
#region GetSharedValue<TItem, TProperty>(IList<TItem> items, Func<TItem, TProperty> getPropertyDelegate, TProperty nonSharedValue)
/// <summary>
/// Gets a value for a certain property which represents a
/// <i>shared</i> value for all <typeparamref name="TItem"/>
/// instances in <paramref name="items"/>.<br/>
/// This means, if all wrapped <typeparamref name="TItem"/> instances
/// have the same value for the specific property, this value will
/// be returned. If the values differ, <paramref name="nonSharedValue"/>
/// will be returned.
/// </summary>
/// <typeparam name="TItem">The type of the items for which a shared
/// property value is requested.</typeparam>
/// <typeparam name="TProperty">The type of the property for which
/// a shared value is requested.</typeparam>
/// <param name="items">The collection of <typeparamref name="TItem"/>
/// instances for which a shared value is requested.</param>
/// <param name="getPropertyDelegate">A delegate which returns the
/// property value for the requested property. This is used, so that
/// reflection can be avoided for performance reasons. The easiest way
/// is to provide a lambda expression like this:<br/>
/// <code>(item) => item.MyProperty</code><br/>
/// This expression will simply return the value of the
/// <c>MyProperty</c> property of the passed item.</param>
/// <param name="nonSharedValue">The value which should be returned if
/// the values are not equal for all items.</param>
/// <returns>If all <typeparamref name="TItem"/> instances have
/// the same value for the specific property, this value will
/// be returned. If the values differ, <paramref name="nonSharedValue"/>
/// will be returned.</returns>
public static TProperty GetSharedValue<TItem, TProperty>(IList<TItem> items, Func<TItem, TProperty> getPropertyDelegate, TProperty nonSharedValue)
{
if (items == null || items.Count == 0)
return nonSharedValue;
TProperty sharedValue = getPropertyDelegate(items[0]);
for (int i = 1; i < items.Count; i++)
{
TItem currentItem = items[i];
TProperty currentValue = getPropertyDelegate(currentItem);
if (!sharedValue.Equals(currentValue))
return nonSharedValue;
}
return sharedValue;
}
#endregion
#region SetSharedValue<TItem, TProperty>(IList<TItem> a_items, Action<TItem, TProperty> a_setPropertyDelegate, TProperty a_newValue)
/// <summary>
/// Sets the same value for all <typeparamref name="TItem"/>
/// instances in <paramref name="a_items"/>.
/// </summary>
/// <typeparam name="TItem">The type of the items for which a shared
/// property value is requested.</typeparam>
/// <typeparam name="TProperty">The type of the property for which
/// a shared value is requested.</typeparam>
/// <param name="items">The collection of <typeparamref name="TItem"/>
/// instances for which a shared value should be set.</param>
/// <param name="setPropertyDelegate">A delegate which sets the
/// property value for the requested property. This is used, so that
/// reflection can be avoided for performance reasons. The easiest way
/// is to provide a lambda expression like this:<br/>
/// <code>(item, newValue) => item.MyProperty = newValue</code><br/>
/// This expression will simply set the value of the
/// <c>MyProperty</c> property of the passed item to <c>newValue</c>.</param>
/// <param name="newValue">The new value for the property.</param>
public static void SetSharedValue<TItem, TProperty>(IList<TItem> items, Action<TItem, TProperty> setPropertyDelegate, TProperty newValue)
{
if (items == null || items.Count == 0)
return;
foreach (TItem item in items)
{
try
{
setPropertyDelegate(item, newValue);
}
catch (Exception ex)
{
// log/error message here
}
}
}
#endregion
#endregion
}