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,我必须使用MapItemsControl集合,而不是MapElements集合.
该集合绑定到ObservableCollection< PushpinViewModel>对象(Pushpins)在相应的ViewModel中.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个PushpinViewModel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,我调用了Clear()方法.但是……没有任何反应！图钉被清除,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.
那么,问题是什么？显然,ObservableCollection在对其执行了Clear()之后保持对PushpinViewModel对象的引用,因此它们不能被垃圾回收.当然,强制GC执行垃圾收集并没有帮助(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,但是当我指定了Pushpins = null,然后做了更多的事情时,VehiceViewModel被摧毁了.但这对我不起作用,因为我还记得在Clear()之后我在地图上可视化这些引脚时遇到了问题.
你有什么想法会导致这种内存泄漏吗？我如何强迫OC的成员摧毁？也许OC有某种替代方案？
在此先感谢您的帮助！
编辑：
我使用XAML Map Control-https://xamlmapcontrol.codeplex.com/进行了一些测试,结果令人惊讶.添加了> 1000个元素的整体地图性能比原生MapControl差,但是,如果我调用Add()x1000,然后调用Clear(),然后添加()x1000,则PushpinViewModel的终结器调用！内存被释放,应用程序不会崩溃.所以微软的MapControl肯定有问题……
解决方法
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,因为我的应用程序只是将项添加到ObservableCollection并清除它们;它永远不会逐步删除项目.
另请注意,它使用绑定的项的哈希码标记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.这可能不适用于您的情况,但似乎是有效的.
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.目标是我的ObservableCollection对象,它具有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>
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),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
}
}
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