我有一个ObservableCollection类型的项目集合，该集合绑定到视图中的列表控件。
我遇到了这样一种情况：我需要将一系列值添加到该集合的开头。 Collection<T>.Insert说明文档指定每个插入操作都是O(n)操作，并且每次插入还会生成一个CollectionChanged通知。
因此，理想情况下，我希望通过一次移动来整体插入所有项目范围，这意味着只需要对底层列表进行一次洗牌，而且希望只有一个CollectionChanged通知（可能是“重置”）。
Collection<T>没有公开任何方法来实现这一点。 List<T>具有InsertRange()方法，但是IList<T>通过其Items属性被Collection<T>公开时却没有提供该方法。
是否有任何方法可以做到这一点？
ObservableCollection公开了一个受保护的Items属性，它是底层集合而没有通知语义。这意味着您可以通过继承ObservableCollection来构建满足要求的集合：
class RangeEnabledObservableCollection<T> : ObservableCollection<T>
{
public void InsertRange(IEnumerable<T> items)
{
this.CheckReentrancy();
foreach(var item in items)
this.Items.Add(item);
this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
用法：
void Main()
{
var collection = new RangeEnabledObservableCollection<int>();
collection.CollectionChanged += (s,e) => Console.WriteLine("Collection changed");
collection.InsertRange(Enumerable.Range(0,100));
Console.WriteLine("Collection contains {0} items.", collection.Count);
}
this.OnPropertyChanged(new PropertyChangedEventArgs("Count")); this.OnPropertyChanged(new PropertyChangedEventArgs("Item[]")); - bouvierr如何做到这一点，请看以下示例：
public static void InsertRange<T>(this ObservableCollection<T> collection, IEnumerable<T> items)
{
var enumerable = items as List<T> ?? items.ToList();
if (collection == null || items == null || !enumerable.Any())
{
return;
}
Type type = collection.GetType();
type.InvokeMember("CheckReentrancy", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null, collection, null);
var itemsProp = type.BaseType.GetProperty("Items", BindingFlags.NonPublic | BindingFlags.FlattenHierarchy | BindingFlags.Instance);
var privateItems = itemsProp.GetValue(collection) as IList<T>;
foreach (var item in enumerable)
{
privateItems.Add(item);
}
type.InvokeMember("OnPropertyChanged", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null,
collection, new object[] { new PropertyChangedEventArgs("Count") });
type.InvokeMember("OnPropertyChanged", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null,
collection, new object[] { new PropertyChangedEventArgs("Item[]") });
type.InvokeMember("OnCollectionChanged", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null,
collection, new object[]{ new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset)});
}
这个答案没有显示DataGrid中的新条目。对我有用的是这个OnCollectionChanged：
public class SilentObservableCollection<T> : ObservableCollection<T>
{
public void AddRange(IEnumerable<T> enumerable)
{
CheckReentrancy();
int startIndex = Count;
foreach (var item in enumerable)
Items.Add(item);
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, new List<T>(enumerable), startIndex));
OnPropertyChanged(new PropertyChangedEventArgs("Count"));
OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
}
}
var stuff = new ObservableCollection<Stuff>() {...};
...
// will trigger only 1 OnCollectionChanged event
stuff.ReplaceCollection(newThings);
// equivalent without the extension methods
// stuff.Clear(); // triggers 1 OnCollectionChanged
// foreach (var thing in newThings)
// stuff.Add(thing); // triggers multiple OnCollectionChanged
ObservableCollectionExtensions.cs是一个文件：
using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
namespace System.Collections.ObjectModel
{
public static class ObservableCollectionExtensions
{
private static BindingFlags ProtectedMember = BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic;
private static BindingFlags ProtectedProperty = BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic;
/// <summary>
/// Insert a collection without triggering OnCollectionChanged event
/// </summary>
private static void InsertWithoutNotify<T>(this ObservableCollection<T> collection, IEnumerable<T> items, int index = -1)
{
if (collection == null || items == null || !items.Any()) return;
Type type = collection.GetType();
type.InvokeMember("CheckReentrancy", ProtectedMember, null, collection, null);
PropertyInfo itemsProp = type.BaseType.GetProperty("Items", ProtectedProperty);
IList<T> protectedItems = itemsProp.GetValue(collection) as IList<T>;
// Behave the same as Add if no index is being passed
int start = index > -1 ? index : protectedItems.Count();
int end = items.Count();
for (int i = 0; i < end; i++)
{
protectedItems.Insert(start + i, items.ElementAt(i));
}
type.InvokeMember("OnPropertyChanged", ProtectedMember, null,
collection, new object[] { new PropertyChangedEventArgs("Count") });
type.InvokeMember("OnPropertyChanged", ProtectedMember, null,
collection, new object[] { new PropertyChangedEventArgs("Item[]") });
}
public static void AddRange<T>(this ObservableCollection<T> collection, IEnumerable<T> items)
{
if (collection == null || items == null || !items.Any()) return;
Type type = collection.GetType();
InsertWithoutNotify(collection, items);
type.InvokeMember("OnCollectionChanged", ProtectedMember, null,
collection, new object[] {
// Notify that we've added new items into the collection
new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset)
});
}
public static void InsertRange<T>(this ObservableCollection<T> collection, int index, IEnumerable<T> items)
{
if (collection == null || items == null || !items.Any()) return;
Type type = collection.GetType();
InsertWithoutNotify(collection, items, index);
type.InvokeMember("OnCollectionChanged", ProtectedMember, null,
collection, new object[] {
// Notify that we've added new items into the collection
new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset)
});
}
public static void ReplaceCollection<T>(this ObservableCollection<T> collection, IEnumerable<T> items)
{
if (collection == null || items == null || !items.Any()) return;
Type type = collection.GetType();
// Clear the underlaying list items without triggering a change
PropertyInfo itemsProp = type.BaseType.GetProperty("Items", ProtectedProperty);
IList<T> protectedItems = itemsProp.GetValue(collection) as IList<T>;
protectedItems.Clear();
// Perform the actual update
InsertWithoutNotify(collection, items);
type.InvokeMember("OnCollectionChanged", ProtectedMember, null,
collection, new object[] {
// Notify that we have replaced the entire collection
new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset)
});
}
}
}
示例： 期望步骤为0、10、20、30、40、50、60、70、80、90、100 --> 最小值=0，最大值=100，步骤数=11
static int min = 0;
static int max = 100;
static int steps = 11;
private ObservableCollection<string> restartDelayTimeList = new ObservableCollection<string> (
Enumerable.Range(0, steps).Select(l1 => (min + (max - min) * ((double)l1 / (steps - 1))).ToString())
);
OnPropertyChanged。 - sll