我正在处理在MapControl上显示的大量对象（POI）。我正在帮助自己使用MVVM Light来遵守MVVM方法的规则。
由于我有义务在地图上显示每个对象，因此我必须使用MapItemsControl集合，而不是MapElements集合。
此集合绑定到相应ObservableCollection<PushpinViewModel>中的Pushpins对象（ViewModel）。当我想要刷新Pushpins时，一切都按预期工作。问题是内存泄漏。但首先，一些代码可视化问题：
XAML：
<maps:MapControl x:Name="Map"
x:Uid="MapControl">
<maps:MapItemsControl ItemsSource="{Binding Pushpins}">
<maps:MapItemsControl.ItemTemplate>
<DataTemplate>
<Image Source="{Binding Image}"/>
</DataTemplate>
</maps:MapItemsControl.ItemTemplate>
</maps:MapItemsControl>
MainViewModel：
public class MainViewModel : ViewModelBase
{
public RelayCommand AddCommand { get; set; }
public RelayCommand ClearCommand { get; set; }
public RelayCommand CollectCommand { get; set; }
public ObservableCollection<PushpinViewModel> Pushpins { get; set; }
/* Ctor, initialization of Pushpins and stuff like that */
private void Collect()
{
GC.Collect(2);
GC.WaitForPendingFinalizers();
GC.Collect(2);
PrintCurrentMemory();
}
private void Clear()
{
Pushpins.Clear();
PrintCurrentMemory();
}
private void Add()
{
for (int i = 0; i < 1000; i++)
{
Pushpins.Add(new PushpinViewModel());
}
PrintCurrentMemory();
}
private void PrintCurrentMemory()
{
Logger.Log(String.Format("Total Memory: {0}", GC.GetTotalMemory(true) / 1024.0));
}
}
PushpinViewModel：
public class PushpinViewModel: ViewModelBase
{
public string Image { get { return "/Assets/SomeImage.png"; } }
~PushpinViewModel()
{
Logger.Log("This finalizer never gets called!");
}
}
现在，请考虑以下方案。我添加了Pushpins集合1000 PushpinViewModel个元素。它们被渲染，内存被分配，一切都很好。现在我想清除集合，并添加另一个（在真实场景中不同）1000个元素。所以，我打电话给Clear()方法。但是......没有任何反应！ Pushpins被清除，但PushpinViewModel的终结器未被调用！然后我再次添加1000个元素，我的内存使用量翻倍。
你可以猜到接下来会发生什么。当我重复这个Clear() - Add()程序3-5次我的应用程序崩溃时。
那么，问题是什么？显然ObservableCollection在对PushpinViewModel执行Clear()之后保留对Pushpins = null对象的引用，因此不能对它们进行垃圾回收。当然，强制GC执行垃圾收集也无济于事（有时甚至会使情况变得更糟）。
现在困扰我2天了，我尝试了许多不同的场景来尝试克服这个问题，但说实话，没有任何帮助。
只有一件事物毫无价值 - 我不记得确切的情况，但是当我分配VehiceViewModel，然后做了更多的事情时，Clear()被摧毁了。但这对我不起作用，因为我还记得我在OC之后在地图上显示这些图钉时遇到了问题。
您有什么想法会导致内存泄漏吗？我如何强迫OC的成员摧毁？也许MapControl有某种替代方案？
在此先感谢您的帮助！
编辑：
我使用XAML地图控件进行了一些测试 - https://xamlmapcontrol.codeplex.com/，结果令人惊讶。添加了> 1000个元素的整体地图效果比原始Add()更差，但是，如果我调用Clear() x1000，然后调用Add()，然后调用PushpinViewModel x1000， MapControl的终结器正在调用！内存被释放，应用程序不会崩溃。所以微软的{{1}} ......
答案 0 :(得分：8)
好的，这是我模仿MapItemsControl所做的行为。请注意，这是非常未经测试的 - 它适用于我的应用程序，但实际上并没有在其他任何地方尝试过。我从未测试过RemoveItems函数，因为我的应用只是将项添加到ObservableCollection并清除它们;它永远不会逐步删除项目。
另请注意，它使用绑定项目的哈希码标记XAML图钉;这是它如何识别集合更改时从地图中删除哪些图钉。这可能对您的情况不起作用，但似乎有效。
用法：
注意：NumberedCircle是一个用户控件，它只是一个红色圆圈，在其中显示一个数字;替换为您想要用作图钉的任何XAML控件。 Destinations是我的ObservableCollection个对象，其Number属性（显示在图钉内）和Point属性（图钉位置）。
<map:MapControl>
<i:Interaction.Behaviors>
<behaviors:PushpinCollectionBehavior ItemsSource="{Binding Path=Destinations}">
<behaviors:PushpinCollectionBehavior.ItemTemplate>
<DataTemplate>
<controls:NumberedCircle Number="{Binding Path=Number}" map:MapControl.Location="{Binding Path=Point}" />
</DataTemplate>
</behaviors:PushpinCollectionBehavior.ItemTemplate>
</behaviors:PushpinCollectionBehavior>
</i:Interaction.Behaviors>
</map:MapControl>
代码：
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Xaml.Interactivity;
using Windows.Devices.Geolocation;
using Windows.Foundation;
using Windows.Storage.Streams;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls.Maps;
namespace Foo.Behaviors
{
/// <summary>
/// Behavior to draw pushpins on a map. This effectively replaces MapItemsControl, which is flaky as hell.
/// </summary>
public class PushpinCollectionBehavior : DependencyObject, IBehavior
{
#region IBehavior
public DependencyObject AssociatedObject { get; private set; }
public void Attach(Windows.UI.Xaml.DependencyObject associatedObject)
{
var mapControl = associatedObject as MapControl;
if (mapControl == null)
throw new ArgumentException("PushpinCollectionBehavior can be attached only to MapControl");
AssociatedObject = associatedObject;
mapControl.Unloaded += MapControlUnloaded;
}
public void Detach()
{
var mapControl = AssociatedObject as MapControl;
if (mapControl != null)
mapControl.Unloaded -= MapControlUnloaded;
}
#endregion
#region Dependency Properties
/// <summary>
/// The dependency property of the item that contains the pushpin locations.
/// </summary>
public static readonly DependencyProperty ItemsSourceProperty =
DependencyProperty.Register("ItemsSource", typeof(object), typeof(PushpinCollectionBehavior), new PropertyMetadata(null, OnItemsSourcePropertyChanged));
/// <summary>
/// The item that contains the pushpin locations.
/// </summary>
public object ItemsSource
{
get { return GetValue(ItemsSourceProperty); }
set { SetValue(ItemsSourceProperty, value); }
}
/// <summary>
/// Adds, moves, or removes the pushpin when the item source changes.
/// </summary>
private static void OnItemsSourcePropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
{
var behavior = dependencyObject as PushpinCollectionBehavior;
var mapControl = behavior.AssociatedObject as MapControl;
// add the items
if (behavior.ItemsSource is IList)
behavior.AddItems(behavior.ItemsSource as IList);
else
throw new Exception("PushpinCollectionBehavior needs an IList as the items source.");
// subscribe to changes in the collection
if (behavior.ItemsSource is INotifyCollectionChanged)
{
var items = behavior.ItemsSource as INotifyCollectionChanged;
items.CollectionChanged += behavior.CollectionChanged;
}
}
// <summary>
/// The dependency property of the pushpin template.
/// </summary>
public static readonly DependencyProperty ItemTemplateProperty =
DependencyProperty.Register("ItemTemplate", typeof(DataTemplate), typeof(PushpinCollectionBehavior), new PropertyMetadata(null));
/// <summary>
/// The pushpin template.
/// </summary>
public DataTemplate ItemTemplate
{
get { return (DataTemplate)GetValue(ItemTemplateProperty); }
set { SetValue(ItemTemplateProperty, value); }
}
#endregion
#region Events
/// <summary>
/// Adds or removes the items on the map.
/// </summary>
private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
AddItems(e.NewItems);
break;
case NotifyCollectionChangedAction.Remove:
RemoveItems(e.OldItems);
break;
case NotifyCollectionChangedAction.Reset:
ClearItems();
break;
}
}
/// <summary>
/// Removes the CollectionChanged event handler from the ItemsSource when the map is unloaded.
/// </summary>
void MapControlUnloaded(object sender, RoutedEventArgs e)
{
var items = ItemsSource as INotifyCollectionChanged;
if (items != null)
items.CollectionChanged -= CollectionChanged;
}
#endregion
#region Private Functions
/// <summary>
/// Adds items to the map.
/// </summary>
private void AddItems(IList items)
{
var mapControl = AssociatedObject as MapControl;
foreach (var item in items)
{
var templateInstance = ItemTemplate.LoadContent() as FrameworkElement;
var hashCode = item.GetHashCode();
templateInstance.Tag = hashCode;
templateInstance.DataContext = item;
mapControl.Children.Add(templateInstance);
Tags.Add(hashCode);
}
}
/// <summary>
/// Removes items from the map.
/// </summary>
private void RemoveItems(IList items)
{
var mapControl = AssociatedObject as MapControl;
foreach (var item in items)
{
var hashCode = item.GetHashCode();
foreach (var child in mapControl.Children.Where(c => c is FrameworkElement))
{
var frameworkElement = child as FrameworkElement;
if (hashCode.Equals(frameworkElement.Tag))
{
mapControl.Children.Remove(frameworkElement);
continue;
}
}
Tags.Remove(hashCode);
}
}
/// <summary>
/// Clears items from the map.
/// </summary>
private void ClearItems()
{
var mapControl = AssociatedObject as MapControl;
foreach (var tag in Tags)
{
foreach (var child in mapControl.Children.Where(c => c is FrameworkElement))
{
var frameworkElement = child as FrameworkElement;
if (tag.Equals(frameworkElement.Tag))
{
mapControl.Children.Remove(frameworkElement);
continue;
}
}
}
Tags.Clear();
}
#endregion
#region Private Properties
/// <summary>
/// The object tags of the items this behavior has placed on the map.
/// </summary>
private List<int> Tags
{
get
{
if (_tags == null)
_tags = new List<int>();
return _tags;
}
}
private List<int> _tags;
#endregion
}
}