向Observable Collection添加大容量数据会降低应用程序的性能

Question

我使用WPF Toolkit绘制图形，为了绑定数据以显示绘图，我使用可观察的集合，将数据点添加到集合中，并将此集合作为绘图的项源。

我的问题是，当我向我的集合添加太多数据点时，或者从集合中检索数据点并试图显示绘图时，需要花费大量时间才能显示出来。

我能为这个问题做些什么？

请给我推荐一下，这样可以提高性能。

提前感谢。

Answer 1

ObservableCollection会通知每一个更改，这意味着会发生很多事件，因此会影响性能。你可以使用列表而不是ObservableCollection，但大多数人不推荐它。

public class MainVm:INotifyPropertyChanged
{
    List<Point> _points;
    public List<Point> Points
    {
        get { return _points; }
        set { _points = value; Notify("Points"); }
    }
    public void Notify(string name)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(name));
    }
    public event PropertyChangedEventHandler PropertyChanged;
}

在这种情况下，您必须手动通知视图对列表所做的更改。例如，除了视图模型或视图的构造函数之外，您必须执行以下操作：

Points.Add(new Point());
Points.Add(new Point());
Points.Add(new Point());
//View is not notified yet
var tmp = Points;
Points = null;//View is notified and cleared
Points = tmp;//View is notified and updated

Answer 2

我在这篇文章中使用了ObservableCollection的子类来添加.AddRange，它可以批量添加更新，直到最后都不会触发更新通知。

为了完整起见，我已经从原始帖子中复制了代码，但如果你觉得链接的帖子有用，请投赞成票。

Imports System.Collections.Specialized
Imports System.ComponentModel
Imports System.Collections.ObjectModel
Public Class ObservableRangeCollection(Of T) : Inherits ObservableCollection(Of T) : Implements INotifyCollectionChanging(Of T)
    ''' <summary>
    ''' Initializes a new instance of the System.Collections.ObjectModel.ObservableCollection(Of T) class.
    ''' </summary>
    ''' <remarks></remarks>
    Public Sub New()
        MyBase.New()
    End Sub
    ''' <summary>
    ''' Initializes a new instance of the System.Collections.ObjectModel.ObservableCollection(Of T) class that contains elements copied from the specified collection.
    ''' </summary>
    ''' <param name="collection">collection: The collection from which the elements are copied.</param>
    ''' <exception cref="System.ArgumentNullException">The collection parameter cannot be null.</exception>
    Public Sub New(ByVal collection As IEnumerable(Of T))
        MyBase.New(collection)
    End Sub
    ''' <summary>
    ''' Adds the elements of the specified collection to the end of the ObservableCollection(Of T).
    ''' </summary>
    Public Sub AddRange(ByVal collection As IEnumerable(Of T))
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Add, collection)
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        Dim index = Items.Count - 1
        For Each i In collection
            Items.Add(i)
        Next
        OnCollectionChanged(New NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, collection, index))
    End Sub

    ''' <summary>
    ''' Inserts the collection at specified index.
    ''' </summary>
    Public Sub InsertRange(ByVal index As Integer, ByVal Collection As IEnumerable(Of T))
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Add, Collection)
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        For Each i In Collection
            Items.Insert(index, i)
        Next
        OnCollectionChanged(New NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset))
    End Sub

    ''' <summary>
    ''' Removes the first occurence of each item in the specified collection from ObservableCollection(Of T).
    ''' </summary>
    Public Sub RemoveRange(ByVal collection As IEnumerable(Of T))
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Remove, collection)
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        For Each i In collection
            Items.Remove(i)
        Next
        OnCollectionChanged(New NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset))
    End Sub

    ''' <summary>
    ''' Clears the current collection and replaces it with the specified item.
    ''' </summary>
    Public Sub Replace(ByVal item As T)
        ReplaceRange(New T() {item})
    End Sub
    ''' <summary>
    ''' Clears the current collection and replaces it with the specified collection.
    ''' </summary>
    Public Sub ReplaceRange(ByVal collection As IEnumerable(Of T))
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Replace, Items)
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        Items.Clear()
        For Each i In collection
            Items.Add(i)
        Next
        OnCollectionChanged(New NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset))
    End Sub
    Protected Overrides Sub ClearItems()
        Dim e As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Reset, Items)
        OnCollectionChanging(e)
        If e.Cancel Then Exit Sub
        MyBase.ClearItems()
    End Sub
    Protected Overrides Sub InsertItem(ByVal index As Integer, ByVal item As T)
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Add, item)
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        MyBase.InsertItem(index, item)
    End Sub
    Protected Overrides Sub MoveItem(ByVal oldIndex As Integer, ByVal newIndex As Integer)
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)()
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        MyBase.MoveItem(oldIndex, newIndex)
    End Sub
    Protected Overrides Sub RemoveItem(ByVal index As Integer)
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Remove, Items(index))
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        MyBase.RemoveItem(index)
    End Sub
    Protected Overrides Sub SetItem(ByVal index As Integer, ByVal item As T)
        Dim ce As New NotifyCollectionChangingEventArgs(Of T)(NotifyCollectionChangedAction.Replace, Items(index))
        OnCollectionChanging(ce)
        If ce.Cancel Then Exit Sub
        MyBase.SetItem(index, item)
    End Sub
    Protected Overrides Sub OnCollectionChanged(ByVal e As Specialized.NotifyCollectionChangedEventArgs)
        If e.NewItems IsNot Nothing Then
            For Each i As T In e.NewItems
                If TypeOf i Is INotifyPropertyChanged Then AddHandler DirectCast(i, INotifyPropertyChanged).PropertyChanged, AddressOf Item_PropertyChanged
            Next
        End If
        MyBase.OnCollectionChanged(e)
    End Sub
    Private Sub Item_PropertyChanged(ByVal sender As T, ByVal e As ComponentModel.PropertyChangedEventArgs)
        OnCollectionChanged(New NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset, sender, IndexOf(sender)))
    End Sub
    Public Event CollectionChanging(ByVal sender As Object, ByVal e As NotifyCollectionChangingEventArgs(Of T)) Implements INotifyCollectionChanging(Of T).CollectionChanging
    Protected Overridable Sub OnCollectionChanging(ByVal e As NotifyCollectionChangingEventArgs(Of T))
        RaiseEvent CollectionChanging(Me, e)
    End Sub
End Class

Public Interface INotifyCollectionChanging(Of T)
    Event CollectionChanging(ByVal sender As Object, ByVal e As NotifyCollectionChangingEventArgs(Of T))
End Interface
Public Class NotifyCollectionChangingEventArgs(Of T) : Inherits CancelEventArgs
    Public Sub New()
        m_Action = NotifyCollectionChangedAction.Move
        m_Items = New T() {}
    End Sub
    Public Sub New(ByVal action As NotifyCollectionChangedAction, ByVal item As T)
        m_Action = action
        m_Items = New T() {item}
    End Sub
    Public Sub New(ByVal action As NotifyCollectionChangedAction, ByVal items As IEnumerable(Of T))
        m_Action = action
        m_Items = items
    End Sub
    Private m_Action As NotifyCollectionChangedAction
    Public ReadOnly Property Action() As NotifyCollectionChangedAction
        Get
            Return m_Action
        End Get
    End Property
    Private m_Items As IList
    Public ReadOnly Property Items() As IEnumerable(Of T)
        Get
            Return m_Items
        End Get
    End Property
End Class

Answer 3

man尝试使用wpf-ui虚拟化，这只是渲染你能看到的，所以它可以快速加载数据

ScrollViewer.CanContentScroll = "True"  
VirtualizingStackPanel.IsVirtualizing = "True"  
VirtualizingStackPanel.VirtualizationMode = "Standard"