如何对ObservableCollection进行排序

Question

我有一个ObservableCollection和一个WPF UserControl是Databound.Control是一个图表,显示ObservableCollection中每个BarData类型项的垂直条.

ObservableCollection<BarData>

class BarData
{
   public DateTime StartDate {get; set;}
   public double MoneySpent {get; set;}
   public double TotalMoneySpentTillThisBar {get; set;}
}

现在我想基于StartDate对ObservableCollection进行排序,以便BarData将在集合中按StartDate的顺序递增.然后我可以像这样计算每个BarData中TotalMoneySpentTillThisBar的值 -

var collection = new ObservableCollection<BarData>();
//add few BarData objects to collection
collection.Sort(bar => bar.StartData);    // this is ideally the kind of function I was looking for which does not exist 
double total = 0.0;
collection.ToList().ForEach(bar => {
                                     bar.TotalMoneySpentTillThisBar = total + bar.MoneySpent;
                                     total = bar.TotalMoneySpentTillThisBar; 
                                   }
                            );

我知道我可以使用ICollectionView对数据进行排序,过滤数据但不会改变实际的集合.我需要对实际集合进行排序,以便我可以为每个项目计算TotalMoneySpentTillThisBar.它的价值取决于集合中的项目顺序.

谢谢.

Answer 1

我首先要问你的问题是:你ObservableCollection的排序是非常重要的,还是你真正想要的是将GUI中的显示分类？

我假设目标是有一个"实时"更新的排序显示.然后我看到2个解决方案

1. 得到ICollectionView你的ObservableCollection和排序,如 http://marlongrech.wordpress.com/2008/11/22/icollectionview-explained/

2. 绑定你ObservableCollection的a CollectionViewsource,在它上面添加一个排序,然后使用它CollectionViewSource作为ItemSourcea ListView.

即:

添加此命名空间

xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"

然后

<CollectionViewSource x:Key='src' Source="{Binding MyObservableCollection, ElementName=MainWindowName}">
    <CollectionViewSource.SortDescriptions>
        <scm:SortDescription PropertyName="MyField" />
    </CollectionViewSource.SortDescriptions>

</CollectionViewSource>

和这样绑定

<ListView ItemsSource="{Binding Source={StaticResource src}}" >

Answer 2

我刚刚创建一个扩展类ObservableCollection,因为随着时间的推移,我也希望其他的功能,我已经习惯了从使用List(Contains,IndexOf,AddRange,RemoveRange,等)

我经常使用类似的东西

MyCollection.Sort(p => p.Name);

这是我的排序实现

/// <summary>
/// Expanded ObservableCollection to include some List<T> Methods
/// </summary>
[Serializable]
public class ObservableCollectionEx<T> : ObservableCollection<T>
{

    /// <summary>
    /// Constructors
    /// </summary>
    public ObservableCollectionEx() : base() { }
    public ObservableCollectionEx(List<T> l) : base(l) { }
    public ObservableCollectionEx(IEnumerable<T> l) : base(l) { }

    #region Sorting

    /// <summary>
    /// Sorts the items of the collection in ascending order according to a key.
    /// </summary>
    /// <typeparam name="TKey">The type of the key returned by <paramref name="keySelector"/>.</typeparam>
    /// <param name="keySelector">A function to extract a key from an item.</param>
    public void Sort<TKey>(Func<T, TKey> keySelector)
    {
        InternalSort(Items.OrderBy(keySelector));
    }

    /// <summary>
    /// Sorts the items of the collection in descending order according to a key.
    /// </summary>
    /// <typeparam name="TKey">The type of the key returned by <paramref name="keySelector"/>.</typeparam>
    /// <param name="keySelector">A function to extract a key from an item.</param>
    public void SortDescending<TKey>(Func<T, TKey> keySelector)
    {
        InternalSort(Items.OrderByDescending(keySelector));
    }

    /// <summary>
    /// Sorts the items of the collection in ascending order according to a key.
    /// </summary>
    /// <typeparam name="TKey">The type of the key returned by <paramref name="keySelector"/>.</typeparam>
    /// <param name="keySelector">A function to extract a key from an item.</param>
    /// <param name="comparer">An <see cref="IComparer{T}"/> to compare keys.</param>
    public void Sort<TKey>(Func<T, TKey> keySelector, IComparer<TKey> comparer)
    {
        InternalSort(Items.OrderBy(keySelector, comparer));
    }

    /// <summary>
    /// Moves the items of the collection so that their orders are the same as those of the items provided.
    /// </summary>
    /// <param name="sortedItems">An <see cref="IEnumerable{T}"/> to provide item orders.</param>
    private void InternalSort(IEnumerable<T> sortedItems)
    {
        var sortedItemsList = sortedItems.ToList();

        foreach (var item in sortedItemsList)
        {
            Move(IndexOf(item), sortedItemsList.IndexOf(item));
        }
    }

    #endregion // Sorting
}

Answer 3

排序ObservableCollection的问题在于,每次更改集合时,都会触发一个事件.因此,对于从一个位置移除项目并将它们添加到另一个位置的排序,最终会发生大量事件.

我认为你最好的选择就是以正确的顺序将内容插入到ObservableCollection中.从集合中删除项目不会影响排序.我掀起了一个快速扩展方法来说明

    public static void InsertSorted<T>(this ObservableCollection<T> collection, T item, Comparison<T> comparison)
    {
        if (collection.Count == 0)
            collection.Add(item);
        else
        {
            bool last = true;
            for (int i = 0; i < collection.Count; i++)
            {
                int result = comparison.Invoke(collection[i], item);
                if (result >= 1)
                {
                    collection.Insert(i, item);
                    last = false;
                    break;
                }
            }
            if (last)
                collection.Add(item);
        }
    }

因此,如果您要使用字符串(例如),代码将如下所示

        ObservableCollection<string> strs = new ObservableCollection<string>();
        Comparison<string> comparison = new Comparison<string>((s1, s2) => { return String.Compare(s1, s2); });
        strs.InsertSorted("Mark", comparison);
        strs.InsertSorted("Tim", comparison);
        strs.InsertSorted("Joe", comparison);
        strs.InsertSorted("Al", comparison);

编辑

如果扩展ObservableCollection并提供自己的插入/添加方法,则可以保持调用相同.像这样的东西:

public class BarDataCollection : ObservableCollection<BarData>
{
    private Comparison<BarData> _comparison = new Comparison<BarData>((bd1, bd2) => { return DateTime.Compare(bd1.StartDate, bd2.StartDate); });

    public new void Insert(int index, BarData item)
    {
        InternalInsert(item);
    }

    protected override void InsertItem(int index, BarData item)
    {
        InternalInsert(item);
    }

    public new void Add(BarData item)
    {
        InternalInsert(item);
    }

    private void InternalInsert(BarData item)
    {
        if (Items.Count == 0)
            Items.Add(item);
        else
        {
            bool last = true;
            for (int i = 0; i < Items.Count; i++)
            {
                int result = _comparison.Invoke(Items[i], item);
                if (result >= 1)
                {
                    Items.Insert(i, item);
                    last = false;
                    break;
                }
            }
            if (last)
                Items.Add(item);
        }
    }
}

插入索引被忽略.

        BarData db1 = new BarData(DateTime.Now.AddDays(-1));
        BarData db2 = new BarData(DateTime.Now.AddDays(-2));
        BarData db3 = new BarData(DateTime.Now.AddDays(1));
        BarData db4 = new BarData(DateTime.Now);
        BarDataCollection bdc = new BarDataCollection();
        bdc.Add(db1);
        bdc.Insert(100, db2);
        bdc.Insert(1, db3);
        bdc.Add(db4);