WPF - 无法将列表框项添加到列表框（初级）

问：

当我尝试将列表框项添加到我的列表框（属性 -> 项 -> [...] -> 我从列表中选择 ListBoxItem -> 添加），然后我没有将项添加到列表中，而是在需要“搜索对象”的地方获得“选择对象”弹出窗口，所以我去：演示框架 -> System.Windows.Controls。-> ListBoxItem，然后我的窗体崩溃（System.NullReferenceException）

然后在这些信息下，我得到了一大堆我不明白的东西：

   w System.Object.GetType()
   w Microsoft.VisualStudio.DesignTools.Utility.Data.ShortToDoubleConverter.Convert(Object value, Type targetType, Object parameter, CultureInfo culture)
   w System.Windows.Data.BindingExpression.TransferValue(Object newValue, Boolean isASubPropertyChange)
   w System.Windows.Data.BindingExpression.Activate(Object item)
   w System.Windows.Data.BindingExpression.AttachToContext(AttachAttempt attempt)
   w System.Windows.Data.BindingExpression.AttachOverride(DependencyObject target, DependencyProperty dp)
   w System.Windows.Data.BindingExpressionBase.OnAttach(DependencyObject d, DependencyProperty dp)
   w System.Windows.StyleHelper.GetInstanceValue(UncommonField`1 dataField, DependencyObject container, FrameworkElement feChild, FrameworkContentElement fceChild, Int32 childIndex, DependencyProperty dp, Int32 i, EffectiveValueEntry& entry)
   w System.Windows.FrameworkTemplate.ReceivePropertySet(Object targetObject, XamlMember member, Object value, DependencyObject templatedParent)
   w System.Windows.FrameworkTemplate.<>c__DisplayClass45_0.<LoadOptimizedTemplateContent>b__3(Object sender, XamlSetValueEventArgs setArgs)
   w System.Xaml.XamlObjectWriter.OnSetValue(Object eventSender, XamlMember member, Object value)
   w System.Xaml.XamlObjectWriter.Logic_ApplyPropertyValue(ObjectWriterContext ctx, XamlMember prop, Object value, Boolean onParent)
   w System.Xaml.XamlObjectWriter.Logic_DoAssignmentToParentProperty(ObjectWriterContext ctx)
   w System.Xaml.XamlObjectWriter.Logic_AssignProvidedValue(ObjectWriterContext ctx)
   w System.Xaml.XamlObjectWriter.WriteEndObject()
   w System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter)
   w System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlObjectWriter objectWriter)
   w System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(DependencyObject container, IComponentConnector componentConnector, IStyleConnector styleConnector, List`1 affectedChildren, UncommonField`1 templatedNonFeChildrenField)
   w System.Windows.FrameworkTemplate.LoadContent(DependencyObject container, List`1 affectedChildren)
   w System.Windows.StyleHelper.ApplyTemplateContent(UncommonField`1 dataField, DependencyObject container, FrameworkElementFactory templateRoot, Int32 lastChildIndex, HybridDictionary childIndexFromChildID, FrameworkTemplate frameworkTemplate)
   w System.Windows.FrameworkTemplate.ApplyTemplateContent(UncommonField`1 templateDataField, FrameworkElement container)
   w System.Windows.FrameworkElement.ApplyTemplate()
   w System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   w System.Windows.UIElement.Measure(Size availableSize)
   w System.Windows.ContextLayoutManager.UpdateLayout()
   w System.Windows.ContextLayoutManager.UpdateLayoutCallback(Object arg)
   w System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   w System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
   w System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
   w System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   w System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

我尝试在 XAML 中手动添加 ListBoxItem，但随后它带有下划线，VS 说：“使用 Items.Source 时操作无效。而是获取对元素的访问，并使用 ItemsControl.ItemsSource 属性更改它们。

代码：

 <Window x:Class="ExperimentWithControls.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
            xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
            xmlns:local="clr-namespace:ExperimentWithControls"
            mc:Ignorable="d"
            Title="Eksperymenty z kontrolkami" Height="450" Width="800">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition/>
                <RowDefinition/>
                <RowDefinition Height="0.5*"/>
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition/>
                <ColumnDefinition/>
            </Grid.ColumnDefinitions>
            <Label Content="Wpisz liczbę" HorizontalAlignment="Left" VerticalAlignment="Top" FontSize="18" RenderTransformOrigin="-0.24,-0.246" Margin="10,10,0,0"/>
            <TextBlock x:Name="number" Grid.Column="1" HorizontalAlignment="Center" TextWrapping="Wrap" Text="Liczba" VerticalAlignment="Center" FontSize="24"/>
            <TextBox x:Name="numberTextBox" HorizontalAlignment="Left" Margin="10,44,0,0" TextWrapping="Wrap" Text="0" VerticalAlignment="Top" Width="120" FontSize="18" TextChanged="numberTextBox_TextChanged" PreviewTextInput="numberTextBox_PreviewTextInput"/>
            <ListBox Margin="10,10,10,10" Name="myListBox" HorizontalAlignment="Center" VerticalAlignment="Center" d:ItemsSource="{d:SampleData ItemCount=5}">
    
        </Grid>
    </Window>

手动尝试过：

<ListBox Margin="10,10,10,10" Name="myListBox" HorizontalAlignment="Center" VerticalAlignment="Center" d:ItemsSource="{d:SampleData ItemCount=5}">
<ListBoxItem Content="1"></ListBoxItem>
</ListBox>

但这行不通。

我搜索过很多帖子，但每个人在从 C# 访问 Listbox 时都遇到问题，我只想使用 WPF 创建非常基本的表单。也许我没有安装某些东西，但奇怪的是，我可以将 ListBox 添加到窗体中，但无法添加 ListBox Item。