可观察的链表 [英] Observable LinkedList
问题描述
在WPF应用程序中，我有一个ItemsControl，其项值取决于显示的项.
In my WPF app, I have an ItemsControl whose items values are dependant upon the previous item displayed.
ViewModel是一个音频文件，分为可变长度的部分，我需要以这种方式显示它，在右侧显示一个DateTime，这就是我需要计算的内容(我只知道每个部分的长度，需要计算它的开始和结束的实际时间，以及ItemsControl上的位置.
The ViewModel is an audio file split into parts of variable length, and i need to display it in such manner, with a DateTime displayed on the right, and that's what i need to calculate (I only know each part's length, i need to calculate the actual time it starts and ends, and the position on the ItemsControl).
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我的第一个方法是使用ObservableCollection<MyviewModel>，但很快就发生了一些恐怖事件:
My first approach was to use an ObservableCollection<MyviewModel> but soon enough some horrors occured :
5向多重绑定，其中为IMultiValueConverter，我将计算要返回的值并将DataContext的属性设置为该值，因为我在运行时只知道前一个元素.
5-way multibinding in which's IMultiValueConverter I'd calculate the value to return and set a property of the DataContext to that value, because I only knew the previous element at runtime.
上一个元素是通过Relativesource.PreviousData上的绑定发送的.
The previous element was sent using a binding on Relativesource.PreviousData.
现在我的问题是，在Converter中设置了一个值(这显然是一件坏事)，并使其真正起作用后，常规Collection的元素中没有顺序的概念，因此当深入时当我想在其余部分中间添加音频部分时，显示屏会混乱.
Now my problem is that after setting a value from the Converter (which is obviously a bad thing), and actually getting it to work, a regular Collection doesn't have a notion of order in its elements, so when further down the road when i want to add an audio part in the middle of the rest, the display is messed up.
此外，当我实现更多的业务逻辑时，我可能需要访问在此转换器中计算出的音频部分的开始和结束，如果还没有显示该怎么办...?
Furthermore, when I'll implement more business logic, I may need to access the audio parts's start and end that are calculated in this converter, and what if it's not displayed yet...?
所以这种方法在几个层面上都是错误的.
So that approach was wrong on several levels.
那是我开始谷歌搜索并发现有关LinkedList的地方.现在，我正在尝试制作一个基本上是Observable LinkedList的类(我不需要它是通用的):
That's where i started googling and found out about LinkedList. Now I'm trying to make a class that is basically an Observable LinkedList (I don't need it to be generic):
public class ObservableSegmentLinkedList : LinkedList<MyViewModel>, INotifyCollectionChanged
{
//Overrides ???
#region INotifyCollectionChanged Members
public event NotifyCollectionChangedEventHandler CollectionChanged;
public void OnNotifyCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (CollectionChanged != null)
{
CollectionChanged(this, e);
}
}
#endregion
}
问题的核心是我无法覆盖修改集合的方法(Addfirst，AddLast等)，因此无法正确调用OnNotifyCollectionChanged ...
And the heart of the problem is that i can't override the methods that modify the collection (Addfirst, AddLast etc), so i can't call OnNotifyCollectionChanged properly...
所以我想我可以为每种方法重载，但这听起来很讨厌...
So I'm thinking i could make overloads for each of these methods, but that sounds quite nasty...
简而言之:我需要某种集合，其中每个项目都知道上一项的详细信息，以便计算其自身的属性之一.
有任何线索吗?这甚至是一个好的解决方案吗?
Any clues? is this even a good solution?
谢谢！
附录，ViewModel看起来像:
Appendix, the ViewModel looks like:
public class MyViewModel : INotifyPropertyChanged
{
private DateTime m_SegmentLength;
public DateTime SegmentLength
{
get { return m_SegmentLength; }
set
{
m_SegmentLength = value;
NotifyPropertyChanged("SegmentLength");
}
}
private DateTime m_SegmentAdvert;
public DateTime SegmentAdvert
{
get { return m_SegmentAdvert; }
set
{
m_SegmentAdvert = value;
NotifyPropertyChanged("SegmentAdvert");
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String prop)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(prop));
}
#endregion
}
我想我将尝试结合Thomas和Will的答案:我将使用composition(即我在自定义对象中保留LinkedList的实例，而不是从其继承)并重新定义要使用的方法( AddAfter，AddFirst等)，在其中，在调用实际的LinkedList方法之后，我将只调用OnNotifyPropertychanged.这需要一些工作，但是我想我的问题不会有任何优雅的解决方案...
i think i will try to combine Thomas and Will's answers: I'll use composition (i.e I keep an instance of LinkedList in my custom object instead of inheriting from it) and redefine methods that are meant to be used (AddAfter, AddFirst etc) in which i'll just call OnNotifyPropertychanged after calling the actual LinkedList method. It's a bit of work but i guess there won't be any elegant solution to my problem...
推荐答案
好吧，我制作了一个支持IEnumerable的自定义泛型类，并且将其用作LinkedList<T>，唯一的区别是WPF得到了通知了更改.
Ok now, I made a custom generic class that supports IEnumerable and is used as if it was a LinkedList<T>, with the only difference that WPF gets notified of the changes.
请注意，此解决方案仅适用于相当小的集合，我最多只能管理大约30个元素，所以对我来说很好，但是每次修改此集合时，它都被视为重置".
Please note that this solution only works for a reasonably small collection, I only have to manage around 30 elements max, so it's fine for me, but everytime you modify this collection, it is considered "Reset".
解决方法在这里:
/// <summary>
/// This class is a LinkedList that can be used in a WPF MVVM scenario. Composition was used instead of inheritance,
/// because inheriting from LinkedList does not allow overriding its methods.
/// </summary>
/// <typeparam name="T"></typeparam>
public class ObservableLinkedList<T> : INotifyCollectionChanged, IEnumerable
{
private LinkedList<T> m_UnderLyingLinkedList;
#region Variables accessors
public int Count
{
get { return m_UnderLyingLinkedList.Count; }
}
public LinkedListNode<T> First
{
get { return m_UnderLyingLinkedList.First; }
}
public LinkedListNode<T> Last
{
get { return m_UnderLyingLinkedList.Last; }
}
#endregion
#region Constructors
public ObservableLinkedList()
{
m_UnderLyingLinkedList = new LinkedList<T>();
}
public ObservableLinkedList(IEnumerable<T> collection)
{
m_UnderLyingLinkedList = new LinkedList<T>(collection);
}
#endregion
#region LinkedList<T> Composition
public LinkedListNode<T> AddAfter(LinkedListNode<T> prevNode, T value)
{
LinkedListNode<T> ret = m_UnderLyingLinkedList.AddAfter(prevNode, value);
OnNotifyCollectionChanged();
return ret;
}
public void AddAfter(LinkedListNode<T> node, LinkedListNode<T> newNode)
{
m_UnderLyingLinkedList.AddAfter(node, newNode);
OnNotifyCollectionChanged();
}
public LinkedListNode<T> AddBefore(LinkedListNode<T> node, T value)
{
LinkedListNode<T> ret = m_UnderLyingLinkedList.AddBefore(node, value);
OnNotifyCollectionChanged();
return ret;
}
public void AddBefore(LinkedListNode<T> node, LinkedListNode<T> newNode)
{
m_UnderLyingLinkedList.AddBefore(node, newNode);
OnNotifyCollectionChanged();
}
public LinkedListNode<T> AddFirst(T value)
{
LinkedListNode<T> ret = m_UnderLyingLinkedList.AddFirst(value);
OnNotifyCollectionChanged();
return ret;
}
public void AddFirst(LinkedListNode<T> node)
{
m_UnderLyingLinkedList.AddFirst(node);
OnNotifyCollectionChanged();
}
public LinkedListNode<T> AddLast(T value)
{
LinkedListNode<T> ret = m_UnderLyingLinkedList.AddLast(value);
OnNotifyCollectionChanged();
return ret;
}
public void AddLast(LinkedListNode<T> node)
{
m_UnderLyingLinkedList.AddLast(node);
OnNotifyCollectionChanged();
}
public void Clear()
{
m_UnderLyingLinkedList.Clear();
OnNotifyCollectionChanged();
}
public bool Contains(T value)
{
return m_UnderLyingLinkedList.Contains(value);
}
public void CopyTo(T[] array, int index)
{
m_UnderLyingLinkedList.CopyTo(array, index);
}
public bool LinkedListEquals(object obj)
{
return m_UnderLyingLinkedList.Equals(obj);
}
public LinkedListNode<T> Find(T value)
{
return m_UnderLyingLinkedList.Find(value);
}
public LinkedListNode<T> FindLast(T value)
{
return m_UnderLyingLinkedList.FindLast(value);
}
public Type GetLinkedListType()
{
return m_UnderLyingLinkedList.GetType();
}
public bool Remove(T value)
{
bool ret = m_UnderLyingLinkedList.Remove(value);
OnNotifyCollectionChanged();
return ret;
}
public void Remove(LinkedListNode<T> node)
{
m_UnderLyingLinkedList.Remove(node);
OnNotifyCollectionChanged();
}
public void RemoveFirst()
{
m_UnderLyingLinkedList.RemoveFirst();
OnNotifyCollectionChanged();
}
public void RemoveLast()
{
m_UnderLyingLinkedList.RemoveLast();
OnNotifyCollectionChanged();
}
#endregion
#region INotifyCollectionChanged Members
public event NotifyCollectionChangedEventHandler CollectionChanged;
public void OnNotifyCollectionChanged()
{
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
#endregion
#region IEnumerable Members
IEnumerator IEnumerable.GetEnumerator()
{
return (m_UnderLyingLinkedList as IEnumerable).GetEnumerator();
}
#endregion
}
正如@AndrewS在评论中所提到的，应将LinkedListNode替换为自定义类，该类从其List属性返回ObservableLinkedList.
As mentionned by @AndrewS in the comments, LinkedListNode should be replaced with a custom class that returns an ObservableLinkedList from its List property.
这篇关于可观察的链表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
