1
集合的正确顺序我有一个简单的域对象：维护序
class FavoriteFood
{
public string Name;
public int Ordinal;
}
我想有保持正确的顺序此域对象的集合。例如，假设4克最喜欢的食物：
Name: Banana, Ordinal: 1
Name: Orange, Ordinal: 2
Name: Pear, Ordinal: 3
Name: Watermelon, Ordinal: 4
如果我改变梨的顺序，以4应改变西瓜的序数下降到3
如果我添加一个新的最喜爱的食物（草莓）与序号3它应该转移梨最多4和西瓜高达5
如果我改变梨的序号为2应改变橙色至3。
如果我改变西瓜的序号为1，香蕉会一下子提高到2，橙会涨到3，梨会涨到4.
完成此操作的最佳方法是什么？
UPDATE：域对象的名称属性是动态的，并基于用户输入。该对象必须具有此序号属性，因为用户可以更改其最喜欢的食物的显示顺序。这个序号值保存在数据库中，当填充结构时，我不能保证这些项目是按照他们的序号添加的。
我遇到的麻烦是当底层域对象发生变化时，没有更新列表中其余项的好方法。例如：
var favoriteFoods = new List<FavoriteFood>();
var banana = new FavoriteFood { Name = "Banana", Ordinal = 1};
favoriteFoods.Add(banana);
favoriteFoods.Add(new FavoriteFood { Name = "Orange", Ordinal = 2 });
banana.Ordinal = 2;
// at this point both Banana and Orange have the same ordinal in the list. How can we make sure that Orange's ordinal gets updated too?
到目前为止，我已经尝试过做它的工作原理如下：
class FavoriteFood : INotifyPropertyChanging
{
public string Name;
public int Ordinal
{
get { return this.ordinal; }
set
{
var oldValue = this.ordinal;
if (oldValue != value && this.PropertyChanging != null)
{
this.PropertyChanging(new FavoriteFoodChangingObject { NewOrdinal = value, OldOrdinal = oldValue }, new PropertyChangingEventArgs("Ordinal"));
}
this.ordinal = value;
}
}
internal struct FavoriteFoodChangingObject
{
internal int NewOrdinal;
internal int OldOrdinal;
}
// THIS IS A TEMPORARY WORKAROUND
internal int ordinal;
public event PropertyChangingEventHandler PropertyChanging;
}
public class FavoriteFoodCollection : IEnumerable<FavoriteFood>
{
private class FavoriteFoodOrdinalComparer : IComparer<FavoriteFood>
{
public int Compare(FavoriteFood x, FavoriteFood y)
{
return x.Ordinal.CompareTo(y.Ordinal);
}
}
private readonly SortedSet<FavoriteFood> underlyingList = new SortedSet<FavoriteFood>(new FavoriteFoodOrdinalComparer());
public IEnumerator<FavoriteFood> GetEnumerator()
{
return this.underlyingList.GetEnumerator();
}
public void AddRange(IEnumerable<FavoriteFood> items)
{
foreach (var i in items)
{
this.underlyingList.Add(i);
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
private void UpdateOrdinalsDueToRemoving(FavoriteFood item)
{
foreach (var i in this.underlyingList.Where(x => x.Ordinal > item.Ordinal))
{
i.ordinal--;
}
}
public void Remove(FavoriteFood item)
{
this.underlyingList.Remove(item);
this.UpdateOrdinalsDueToRemoving(item);
}
public void Add(FavoriteFood item)
{
this.UpdateOrdinalsDueToAdding(item);
this.underlyingList.Add(item);
item.PropertyChanging += this.item_PropertyChanging;
}
private void item_PropertyChanging(object sender, PropertyChangingEventArgs e)
{
if (e.PropertyName.Equals("Ordinal"))
{
var ordinalsChanging = (FavoriteFood.FavoriteFoodChangingObject)sender;
this.UpdateOrdinalsDueToEditing(ordinalsChanging.NewOrdinal, ordinalsChanging.OldOrdinal);
}
}
private void UpdateOrdinalsDueToEditing(int newOrdinal, int oldOrdinal)
{
if (newOrdinal > oldOrdinal)
{
foreach (var i in this.underlyingList.Where(x => x.Ordinal <= newOrdinal && x.Ordinal > oldOrdinal))
{
//i.Ordinal = i.Ordinal - 1;
i.ordinal--;
}
}
else if (newOrdinal < oldOrdinal)
{
foreach (var i in this.underlyingList.Where(x => x.Ordinal >= newOrdinal && x.Ordinal < oldOrdinal))
{
//i.Ordinal = i.Ordinal + 1;
i.ordinal++;
}
}
}
private void UpdateOrdinalsDueToAdding(FavoriteFood item)
{
foreach (var i in this.underlyingList.Where(x => x.Ordinal >= item.Ordinal))
{
i.ordinal++;
}
}
}
这工作好了，但使用内部有序场的是一个奇怪的解决方法。这是需要的，以便PropertyChangingEvent不会无限增加。
你有什么试过？什么没有用？你最擅长的是什么？大多数可读？最快的？还有别的吗？ – Oded 2011-06-03 20:08:00