錯誤實行設計時間數據模板

Question

我想在WPF GridView的設計窗口中顯示的虛擬數據，發現了一個類似的例子：Answer: Design time data for datatemplate in xaml - Stack Overflow

我創建了一個新的WPF應用程序（.NET框架4.6.1）命名WpfDataTemplate並將該示例的代碼片段複製到MainWindow.xaml.cs和MainWindow.xaml中。所有新增內容均在##的評論中註明。

意外行爲：

1. 線<local:MyMockClass x:Key="DesignViewModel" />產生錯誤「不設置到對象的實例對象引用」。

2. test text #字符串不會顯示在設計器中。

3. test text #字符串在運行時不顯示在窗口中。

問題：

1. 什麼是錯誤的原因是什麼？

2. 我需要更改代碼才能按預期工作？

---

MainWindow.xaml

<Window x:Class="WpfDataTemplate.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:WpfDataTemplate" 
    mc:Ignorable="d" 
    Title="MainWindow" Height="350" Width="525"> 
<!-- ## BEGIN ADD --> 
<Window.Resources> 
    <local:MyMockClass x:Key="DesignViewModel" /> 
</Window.Resources> 
<!-- ## END ADD --> 
<Grid> 
    <!-- ## BEGIN ADD --> 
    <ListBox x:Name="standardLayoutListBox" 
      d:DataContext="{Binding Source={StaticResource DesignViewModel}}" 
      ItemsSource="{Binding MyListBoxItems}"> 
     <ListBox.ItemTemplate> 
      <DataTemplate> 
       <Grid> 
        <Grid.RowDefinitions> 
         <RowDefinition /> 
         <RowDefinition /> 
        </Grid.RowDefinitions> 
        <Label Grid.Column="0" Content="{Binding text1}" /> 
        <Label Grid.Column="1" Content="{Binding text2}" /> 
       </Grid> 
      </DataTemplate> 
     </ListBox.ItemTemplate> 
    </ListBox> 
    <!-- ## END ADD --> 
</Grid> 

MainWindow.xaml.cs

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Threading.Tasks; 
using System.Windows; 
using System.Windows.Controls; 
using System.Windows.Data; 
using System.Windows.Documents; 
using System.Windows.Input; 
using System.Windows.Media; 
using System.Windows.Media.Imaging; 
using System.Windows.Navigation; 
using System.Windows.Shapes; 
// ## BEGIN ADD 
using System.Collections.ObjectModel; 
// ## END ADD 

namespace WpfDataTemplate 
{ 
    // ## BEGIN ADD 
    public class MyMockClass 
    { 
     public MyMockClass() 
     { 
      MyListBoxItems.Add(new MyDataClass() { text1 = "test text 1", text2 = "test text 2" }); 
      MyListBoxItems.Add(new MyDataClass() { text1 = "test text 3", text2 = "test text 4" }); 
     } 
     public ObservableCollection<MyDataClass> MyListBoxItems { get; set; } 
    } 

    public class MyDataClass 
    { 
     public string text1 { get; set; } 
     public string text2 { get; set; } 
    } 
    // ## END ADD 

    /// <summary> 
    /// Interaction logic for MainWindow.xaml 
    /// </summary> 
    public partial class MainWindow : Window 
    { 
     public MainWindow() 
     { 
      InitializeComponent(); 
     } 
    } 
} 

Answer 1

首先，您需要在您的MyMockClass中初始化您的收藏。

public class MyMockClass 
{ 
    public MyMockClass() 
    { 
     MyListBoxItems = new ObservableCollection<MyDataClass>() 
     MyListBoxItems.Add(new MyDataClass() { text1 = "test text 1", text2 = "test text 2" }); 
     MyListBoxItems.Add(new MyDataClass() { text1 = "test text 3", text2 = "test text 4" }); 
    } 
    public ObservableCollection<MyDataClass> MyListBoxItems { get; set; } 
} 

我使用設計實例在我的窗前，像這樣：

d:DataContext="{d:DesignInstance Type=local:MyMockClass, IsDesignTimeCreatable=True}"