c# – 带有ObservableCollection的Windows Phone 8.1 WinRT内存

<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>

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));
    }
}

public class PushpinViewModel: ViewModelBase
{
    public string Image { get { return "/Assets/SomeImage.png"; } }

    ~PushpinViewModel()
    {
        Logger.Log("This finalizer never gets called!");
    }
}

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
    }
}