XAML iOS上的CollectionView绑定问题(在Android或Windows上工作正常)

wi3ka0sx  于 2023-09-28  发布在  iOS
关注(0)|答案(1)|浏览(111)

这几天来我一直碰到这个问题。
我有一个包含CollectionView的ContentView：

<CollectionView
        VerticalScrollBarVisibility="Never"
        SelectionMode="None"
        ItemsSource="{Binding Source={RelativeSource AncestorType={x:Type ContentView}}, Path=NumberList}">
    
        <CollectionView.ItemTemplate>
            <DataTemplate>
               [...]
            </DataTemplate>
        </CollectionView.ItemTemplate>
    </CollectionView>

此CollectionView的ItemsSource绑定到BindableProperty（该属性位于ContenView的后台代码中）：

public static readonly BindableProperty NumberListProperty =
        BindableProperty.Create(nameof(NumberList), typeof(ObservableCollection<int?>), typeof(NumberPicker));

    public ObservableCollection<int?> NumberList
    {
        get { return (ObservableCollection<int?>)GetValue(NumberListProperty); }
        set { SetValue(NumberListProperty, value); }
    }

所有这些在Android或Windows上都可以正常工作，但是一旦在iOS上显示视图，我就会崩溃（调试停止）。
在输出窗口中，我有一个异常，它对我没有多大帮助：

An error occurred: 'Value cannot be null. (Parameter 'key')'. Callstack: '   at System.Collections.Generic.Dictionary`2[[System.Object, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].FindValue(Object key)
   at System.Collections.Generic.Dictionary`2[[System.Object, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].TryGetValue(Object key, TemplatedCell& value)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].CreateMeasurementCell(NSIndexPath indexPath)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetPrototype()
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewLayout.DetermineCellSize()
   at Microsoft.Maui.Controls.Handlers.Items.ListViewLayout.ConstrainTo(CGSize size)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewLayout.SetInitialConstraints(CGSize size)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].EnsureLayoutInitialized()
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ViewDidLoad()
   at UIKit.UIViewController.get_View()
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewHandler`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].CreatePlatformView()
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[UIKit.UIView, Microsoft.iOS, Version=16.4.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]].OnCreatePlatformView()
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewHandler`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].OnCreatePlatformView()
   at Microsoft.Maui.Handlers.ViewHandler.OnCreatePlatformElement()
   at Microsoft.Maui.Handlers.ElementHandler.CreatePlatformElement()
   at Microsoft.Maui.Handlers.ElementHandler.SetVirtualView(IElement view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[UIKit.UIView, Microsoft.iOS, Version=16.4.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]].SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[UIKit.UIView, Microsoft.iOS, Version=16.4.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.LayoutHandler.SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.ILayout, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.LayoutView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.ContentViewHandler.UpdateContent(IContentViewHandler handler)
   at Microsoft.Maui.Handlers.ContentViewHandler.MapContent(IContentViewHandler handler, IContentView page)
   at Microsoft.Maui.PropertyMapper`2.<>c__DisplayClass5_0[[Microsoft.Maui.IContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Handlers.IContentViewHandler, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].<Add>b__0(IElementHandler h, IElement v)
   at Microsoft.Maui.PropertyMapper.UpdatePropertyCore(String key, IElementHandler viewHandler, IElement virtualView)
   at Microsoft.Maui.PropertyMapper.UpdateProperties(IElementHandler viewHandler, IElement virtualView)
   at Microsoft.Maui.Handlers.ElementHandler.SetVirtualView(IElement view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.IContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.ContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ContentViewHandler.SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.IContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.ContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.LayoutHandler.SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.ILayout, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.LayoutView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.LayoutHandler.SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.ILayout, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.LayoutView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.ScrollViewHandler.UpdateContentView(IScrollView scrollView, IScrollViewHandler handler, ICrossPlatformLayout crossPlatformLayout)
   at Microsoft.Maui.Handlers.ScrollViewHandler.MapContent(IScrollViewHandler handler, IScrollView scrollView)
   at Microsoft.Maui.PropertyMapper`2.<>c__DisplayClass5_0[[Microsoft.Maui.IScrollView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Handlers.IScrollViewHandler, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].<Add>b__0(IElementHandler h, IElement v)
   at Microsoft.Maui.PropertyMapper.UpdatePropertyCore(String key, IElementHandler viewHandler, IElement virtualView)
   at Microsoft.Maui.PropertyMapper.UpdateProperties(IElementHandler viewHandler, IElement virtualView)
   at Microsoft.Maui.Handlers.ElementHandler.SetVirtualView(IElement view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.IScrollView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[UIKit.UIScrollView, Microsoft.iOS, Version=16.4.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]].SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.IScrollView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[UIKit.UIScrollView, Microsoft.iOS, Version=16.4.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.LayoutHandler.SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.ILayout, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.LayoutView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ElementExtensions.ToPlatform(IElement view, IMauiContext context)
   at Microsoft.Maui.Handlers.ContentViewHandler.UpdateContent(IContentViewHandler handler)
   at Microsoft.Maui.Handlers.ContentViewHandler.MapContent(IContentViewHandler handler, IContentView page)
   at Microsoft.Maui.PropertyMapper`2.<>c__DisplayClass5_0[[Microsoft.Maui.IContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Handlers.IContentViewHandler, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].<Add>b__0(IElementHandler h, IElement v)
   at Microsoft.Maui.PropertyMapper.UpdatePropertyCore(String key, IElementHandler viewHandler, IElement virtualView)
   at Microsoft.Maui.PropertyMapper.UpdateProperties(IElementHandler viewHandler, IElement virtualView)
   at Microsoft.Maui.Handlers.ElementHandler.SetVirtualView(IElement view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.IContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.ContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ContentViewHandler.SetVirtualView(IView view)
   at Microsoft.Maui.Handlers.ViewHandler`2[[Microsoft.Maui.IContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[Microsoft.Maui.Platform.ContentView, Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetVirtualView(IElement view)
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Platform.ElementExtensions.ToHandler(IElement view, IMauiContext context)
   at Microsoft.Maui.Platform.ViewExtensions.ToHandler(IView view, IMauiContext context)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.PushPage(Page page, Boolean animated, TaskCompletionSource`1 completionSource)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.OnPushRequested(NavigationRequestedEventArgs e)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.OnNavigationRequested(Object sender, NavigationRequestedEventArgs e)
   at Microsoft.Maui.Controls.ShellSection.InvokeNavigationRequest(NavigationRequestedEventArgs args)
   at Microsoft.Maui.Controls.ShellSection.OnPushAsync(Page page, Boolean animated)
   at Microsoft.Maui.Controls.ShellSection.PushStackOfPages(List`1 pages, Nullable`1 animate)
   at Microsoft.Maui.Controls.ShellSection.GoToAsync(ShellNavigationRequest request, ShellRouteParameters queryData, IServiceProvider services, Nullable`1 animate, Boolean isRelativePopping)
   at Microsoft.Maui.Controls.ShellNavigationManager.GoToAsync(ShellNavigationParameters shellNavigationParameters, ShellNavigationRequest navigationRequest)

我做的一些测试：

如果我将列表的类型从ObservableCollection更改为List，它不会改变任何东西。
如果我简化ItemTemplate（例如，使用一个显示“hello”的简单标签），它不会改变任何东西。
如果我将CollectionView转换为VerticalStackLayout，它就可以工作（但这不是我想要的）。
简而言之，我被困住了。提前感谢您的见解。

编辑：

小精，我在.net 8开发的。直到最近我还在使用.net 7，但我在iOS上遇到了其他问题（包括键盘与文本框重叠）。

xaml

1条答案

按热度按时间
gc0ot86w

gc0ot86w1#

我最终通过将BindableProperty从**“int？“到一个“int”**的列表（并通过重构我的组件的逻辑）。
iOS CollectionView似乎不太适应这种可空类型的概念。
因为我对所做的重构很满意，所以我不打算再看下去了。

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