我有一个为Windows Phone 8.1构建的WinRT应用程序。该应用程序具有一个主页面，导航到一个包含项目列表的页面，当用户点击项目时，它会导航到该项目的详细信息页面。事实证明，当用户单击项目然后按返回键时，Windows 10 Mobile上的第一个列表页面实例不会被垃圾回收。在Windows Phone 8.1上，一切都按预期工作。分析工具显示内存快照中的以下根路径。
我会感激任何关于导致此问题的原因以及如何解决它的帮助。
这是页面的完整代码。
从根路径查看，W10M会保持一些对象与其事件挂钩的活性。该页面有一个中心控件和两个项目列表。代码后面有几个事件处理程序。
该应用程序已发布在Windows Store中 - https://www.microsoft.com/en-us/store/p/sc2-master/9n2cjmrsnd8l 编辑：按要求，提供NavigationHelper类（已删除非Windows Phone部分）。
我会感激任何关于导致此问题的原因以及如何解决它的帮助。
这是页面的完整代码。
<Page
x:Class="Medusa.WinRT.RacePage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Medusa.WinRT"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Page.Resources>
<ResourceDictionary>
<Style x:Key="ImageLabelStyle" TargetType="TextBlock">
<Setter Property="Margin" Value="5,0,0,0"/>
<Setter Property="VerticalAlignment" Value="Center" />
<Setter Property="FontFamily" Value="{ThemeResource PhoneFontFamilySemiLight}" />
<Setter Property="FontSize" Value="{ThemeResource TextStyleMediumFontSize}" />
<Setter Property="TextLineBounds" Value="Full" />
<Setter Property="TextWrapping" Value="NoWrap" />
<Setter Property="LineHeight" Value="20" />
<Setter Property="Foreground" Value="{ThemeResource PhoneMidBrush}" />
</Style>
</ResourceDictionary>
</Page.Resources>
<Grid>
<Hub x:Name="pMain" Header="{Binding Title}">
<Hub.Background>
<ImageBrush ImageSource="{Binding BackgroundImagePath}" Stretch="UniformToFill" Opacity="0.3"></ImageBrush>
</Hub.Background>
<HubSection Header="UNITS" HeaderTemplate="{ThemeResource HubSectionHeaderTemplate}">
<DataTemplate>
<ListView Margin="0,0,-12,0" ItemsSource="{Binding Units}" Background="Transparent">
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel x:Name="spUnit" Tapped="spUnit_Tapped" Background="Transparent" Tag="{Binding}">
<StackPanel Orientation="Horizontal" Margin="0,0,0,17">
<Image Width="80" Height="72" Source="{Binding MenuImagePath}" ImageFailed="ImageFailed"></Image>
<Grid Width="270" Tag="{Binding}">
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Row="0" Grid.ColumnSpan="8" Text="{Binding Name}" Style="{ThemeResource ListViewItemTextBlockStyle}"/>
<Image Grid.Row="1" Grid.Column="0" Width="20" Height="20" Source="Assets/icon-mineral.png"></Image>
<TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding MineralCost}" Style="{ThemeResource ImageLabelStyle}"/>
<Image Grid.Row="1" Grid.Column="2" Width="20" Height="20" Source="{Binding Path=RaceGasIconPath}"></Image>
<TextBlock Grid.Row="1" Grid.Column="3" Text="{Binding GasCost}" Style="{ThemeResource ImageLabelStyle}"/>
<Image Grid.Row="1" Grid.Column="4" Width="20" Height="20" Source="{Binding Path=RaceBuildTimeIcon}"></Image>
<TextBlock Grid.Row="1" Grid.Column="5" Text="{Binding BuildTime}" Style="{ThemeResource ImageLabelStyle}"/>
<Image Grid.Row="1" Grid.Column="6" Width="20" Height="20" Source="{Binding Path=RaceSupplyIcon}"></Image>
<TextBlock Grid.Row="1" Grid.Column="7" Text="{Binding SupplyCost}" Style="{ThemeResource ImageLabelStyle}"/>
</Grid>
</StackPanel>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</DataTemplate>
</HubSection>
<HubSection Header="BUILDINGS" HeaderTemplate="{ThemeResource HubSectionHeaderTemplate}">
<DataTemplate>
<ListView Margin="0,0,-12,0" ItemsSource="{Binding Buildings}" Background="Transparent">
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel x:Name="spBuilding" Tapped="spBuilding_Tapped" Tag="{Binding}" Background="Transparent">
<StackPanel Orientation="Horizontal" Margin="0,0,0,17" >
<Image Width="80" Height="72" Source="{Binding MenuImagePath}" ImageFailed="ImageFailed"></Image>
<Grid Width="270">
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
<ColumnDefinition Width="20" />
<ColumnDefinition Width="40" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Row="0" Grid.ColumnSpan="8" Text="{Binding Name}" Style="{ThemeResource ListViewItemTextBlockStyle}"/>
<Image Grid.Row="1" Grid.Column="0" Width="20" Height="20" Source="Assets/icon-mineral.png"></Image>
<TextBlock Grid.Row="1" Grid.Column="1" Text="{Binding MineralCost}" Style="{ThemeResource ImageLabelStyle}"/>
<Image Grid.Row="1" Grid.Column="2" Width="20" Height="20" Source="{Binding Path=RaceGasIconPath}"></Image>
<TextBlock Grid.Row="1" Grid.Column="3" Text="{Binding GasCost}" Style="{ThemeResource ImageLabelStyle}"/>
<Image Grid.Row="1" Grid.Column="4" Width="20" Height="20" Source="{Binding Path=RaceBuildTimeIcon}"></Image>
<TextBlock Grid.Row="1" Grid.Column="5" Text="{Binding BuildTime}" Style="{ThemeResource ImageLabelStyle}"/>
<Image Grid.Row="1" Grid.Column="6" Width="20" Height="20" Source="{Binding Path=RaceSupplyIcon}"></Image>
<TextBlock Grid.Row="1" Grid.Column="7" Text="{Binding SupplyValue}" Style="{ThemeResource ImageLabelStyle}"/>
</Grid>
</StackPanel>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</DataTemplate>
</HubSection>
</Hub>
</Grid>
</Page>
代码后台:
public sealed partial class RacePage : Page
{
private NavigationHelper navigationHelper;
public RacePage()
{
this.InitializeComponent();
navigationHelper = new NavigationHelper(this);
navigationHelper.LoadState += OnNavigationHelperLoadState;
this.Unloaded += RacePage_Unloaded;
}
private void RacePage_Unloaded(object sender, RoutedEventArgs e)
{
DataContext = null;
navigationHelper.LoadState -= OnNavigationHelperLoadState;
navigationHelper = null;
}
private void OnNavigationHelperLoadState(object sender, LoadStateEventArgs e)
{
Initialize((Races)e.NavigationParameter);
}
private void Initialize(Races race)
{
if (DataContext == null)
{
var viewModel = new RaceViewModel(App.Settings.CurrentGameInfo, race);
DataContext = viewModel;
}
}
private void ImageFailed(object sender, ExceptionRoutedEventArgs e)
{
((Image)sender).Source = new BitmapImage(new Uri("ms-appx:///Assets/noimage80x72.png", UriKind.Absolute));
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
navigationHelper.OnNavigatedTo(e);
}
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
navigationHelper.OnNavigatedFrom(e);
}
private void spUnit_Tapped(object sender, TappedRoutedEventArgs e)
{
var unitViewModel = (UnitViewModel)((Panel)sender).Tag;
this.Frame.Navigate(typeof(UnitPage), unitViewModel);
}
private void spBuilding_Tapped(object sender, TappedRoutedEventArgs e)
{
var buildingViewModel = (BuildingViewModel)((Panel)sender).Tag;
this.Frame.Navigate(typeof(BuildingPage), buildingViewModel);
}
}
调试故事（我是如何到达这一点的）
我发布了一个使用WinRT构建的WP8.1和Win10 Mobile应用。当它进入市场后，我进行了更多测试，并发现在W10M上，列表页面上的图像在来回详情页面大约10次后开始滞后（出现一秒钟）。虽然我在W10M上测试了应用，但没有点击那么多才能看到问题，而在开发时，我使用内存较少的WP8.1模拟器进行测试，所以我还没有遇到该问题。该问题在WP8.1上不存在。该问题可在模拟器中重现。
我假设存在某种泄漏并运行了分析工具。我首先注意到PropertyChanged代理的数量正在增加。我想也许是我的ViewModel通过事件处理程序保持了引用。既然我不需要双向数据绑定，我删除了INotifyPropertyChanged实现，但问题仍然存在，代理被替换为称为CustomPropertyImpl的东西（似乎这是用于绑定到POCO的基础设施）。
我随后查看了我的视图模型，以检查它们是否是静态的。但它们不是静态的。我在列表页上挂钩了一个未加载的处理程序，并手动将DataContext设置为null。这减少了泄漏的对象数量，问题在视觉上没有再现，但当我查看分析工具时，列表页仍然存在泄漏。似乎问题仍会发生，但需要加载数百个页面而不是10个。从根路径查看，W10M会保持一些对象与其事件挂钩的活性。该页面有一个中心控件和两个项目列表。代码后面有几个事件处理程序。
该应用程序已发布在Windows Store中 - https://www.microsoft.com/en-us/store/p/sc2-master/9n2cjmrsnd8l 编辑：按要求，提供NavigationHelper类（已删除非Windows Phone部分）。
[Windows.Foundation.Metadata.WebHostHidden]
public class NavigationHelper : DependencyObject
{
private Page Page { get; set; }
private Frame Frame { get { return this.Page.Frame; } }
public NavigationHelper(Page page)
{
this.Page = page;
this.Page.Loaded += (sender, e) =>
{
#if WINDOWS_PHONE_APP
Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
#endif
};
// Undo the same changes when the page is no longer visible
this.Page.Unloaded += (sender, e) =>
{
#if WINDOWS_PHONE_APP
Windows.Phone.UI.Input.HardwareButtons.BackPressed -= HardwareButtons_BackPressed;
#endif
};
}
#region Navigation support
RelayCommand _goBackCommand;
RelayCommand _goForwardCommand;
public RelayCommand GoBackCommand
{
get
{
if (_goBackCommand == null)
{
_goBackCommand = new RelayCommand(
() => this.GoBack(),
() => this.CanGoBack());
}
return _goBackCommand;
}
set
{
_goBackCommand = value;
}
}
public RelayCommand GoForwardCommand
{
get
{
if (_goForwardCommand == null)
{
_goForwardCommand = new RelayCommand(
() => this.GoForward(),
() => this.CanGoForward());
}
return _goForwardCommand;
}
}
public virtual bool CanGoBack()
{
return this.Frame != null && this.Frame.CanGoBack;
}
public virtual bool CanGoForward()
{
return this.Frame != null && this.Frame.CanGoForward;
}
public virtual void GoBack()
{
if (this.Frame != null && this.Frame.CanGoBack) this.Frame.GoBack();
}
public virtual void GoForward()
{
if (this.Frame != null && this.Frame.CanGoForward) this.Frame.GoForward();
}
#if WINDOWS_PHONE_APP
private void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
{
if (this.GoBackCommand.CanExecute(null))
{
e.Handled = true;
this.GoBackCommand.Execute(null);
}
}
#endif
#endregion
#region Process lifetime management
private String _pageKey;
public event LoadStateEventHandler LoadState;
public event SaveStateEventHandler SaveState;
public void OnNavigatedTo(NavigationEventArgs e)
{
var frameState = SuspensionManager.SessionStateForFrame(this.Frame);
this._pageKey = "Page-" + this.Frame.BackStackDepth;
if (e.NavigationMode == NavigationMode.New)
{
// Clear existing state for forward navigation when adding a new page to the
// navigation stack
var nextPageKey = this._pageKey;
int nextPageIndex = this.Frame.BackStackDepth;
while (frameState.Remove(nextPageKey))
{
nextPageIndex++;
nextPageKey = "Page-" + nextPageIndex;
}
// Pass the navigation parameter to the new page
if (this.LoadState != null)
{
this.LoadState(this, new LoadStateEventArgs(e.Parameter, null));
}
}
else
{
// Pass the navigation parameter and preserved page state to the page, using
// the same strategy for loading suspended state and recreating pages discarded
// from cache
if (this.LoadState != null)
{
this.LoadState(this, new LoadStateEventArgs(e.Parameter, (Dictionary<String, Object>)frameState[this._pageKey]));
}
}
}
public void OnNavigatedFrom(NavigationEventArgs e)
{
var frameState = SuspensionManager.SessionStateForFrame(this.Frame);
var pageState = new Dictionary<String, Object>();
if (this.SaveState != null)
{
this.SaveState(this, new SaveStateEventArgs(pageState));
}
frameState[_pageKey] = pageState;
}
#endregion
}
public delegate void LoadStateEventHandler(object sender, LoadStateEventArgs e);
public delegate void SaveStateEventHandler(object sender, SaveStateEventArgs e);
public class LoadStateEventArgs : EventArgs
{
public Object NavigationParameter { get; private set; }
public Dictionary<string, Object> PageState { get; private set; }
public LoadStateEventArgs(Object navigationParameter, Dictionary<string, Object> pageState)
: base()
{
this.NavigationParameter = navigationParameter;
this.PageState = pageState;
}
}
public class SaveStateEventArgs : EventArgs
{
public Dictionary<string, Object> PageState { get; private set; }
public SaveStateEventArgs(Dictionary<string, Object> pageState)
: base()
{
this.PageState = pageState;
}
}