我想扩展在此线程上提出的问题
Binding listbox to observablecollection
通过赋予它持久化数据的能力。除了我安装了 Entity Framework Core 之外，结构基本相同，创建了一个 DbContext 类来保存记录。我添加了一个按钮来将数据集保存到 SQL Server。我没有遇到编译错误，但是当我尝试将数据保存在数据库中时，我遇到了这个运行时异常:
下面列出了整个异常(exception)情况
这是更新后的 Fruit 类:
namespace Fruits.ViewModels
{
[Table("Fruits")]
public class Fruit : ViewModelBase
{
#region Constractor
public Fruit()
{
}
public Fruit(string name, String clrString)
{
FruitName = name;
// Parse colors like so: (Color)ColorConverter.ConvertFromString(clrString);
FruitColor = clrString;
_id = Guid.NewGuid();
}
public Fruit(string name, Color clr)
{
FruitName = name;
FruitColor = clr.ToString();
_id = Guid.NewGuid();
}
#endregion
#region Properties
private Guid _id;
[Key]
public Guid ID
{
get { return _id; }
}
#region FruitName
private string _fruitname;
public string FruitName
{
get
{
return _fruitname;
}
set
{
if (_fruitname != value)
{
_fruitname = value;
OnPropertyChanged("FruitName");
}
}
}
#endregion
#region FruitColor
private String _fruitcolor;
public String FruitColor
{
get
{
return _fruitcolor;
}
set
{
if (_fruitcolor != value)
{
_fruitcolor = value;
OnPropertyChanged("FruitColor");
}
}
}
#endregion
#region Selected Property
private bool _isSelected = true;
// NOTE: I renamed this property
public bool IsSelected
{
get
{
return _isSelected;
}
set
{
if (_isSelected != value)
{
_isSelected = value;
OnPropertyChanged("IsSelected");
}
}
}
#endregion
#endregion
}
}
更新的 MainWindows xaml(添加保存按钮)
<Window x:Class="Fruits.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:Fruits"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<RoutedCommand x:Key="AddFruit" />
<RoutedCommand x:Key='SaveFruit' />
</Window.Resources>
<Window.CommandBindings>
<CommandBinding Command='{StaticResource AddFruit}'
Executed='AddFruitCommandBinding_Executed'
CanExecute='AddFruitCommandBinding_CanExecute' />
<CommandBinding Command='{StaticResource SaveFruit}'
Executed='SaveFruitCommandBinding_Executed'
CanExecute='SaveFruitCommandBinding_CanExecute' />
</Window.CommandBindings>
<Grid>
<StackPanel Orientation='Vertical'
Margin='10'>
<CheckBox IsChecked="{Binding ShowSelectedFruitOnly}">Selected Fruit Only</CheckBox>
<ListBox x:Name='MyList'
ItemsSource="{Binding FruitsView}"
ItemTemplate='{StaticResource FruitTemp}' />
<StackPanel Orientation="Horizontal"
Margin="0,10,0,0">
<Label Width="100">New Name:</Label>
<TextBox Width="200"
Text="{Binding NewFruitName, Mode=TwoWay }"
/>
</StackPanel>
<StackPanel Orientation="Horizontal"
Margin="0,10,0,0">
<Label Width="100">New Color:</Label>
<!--<TextBox Width="200"
Text="{Binding NewFruitColor, UpdateSourceTrigger=PropertyChanged}" />-->
<TextBox Width="200"
Text="{Binding NewFruitColor, Mode=TwoWay }" />
<ContentControl Style="{StaticResource ColorSwatch}"
Margin="2"
VerticalAlignment="Center"
Content="{Binding NewFruitColor}" />
</StackPanel>
<StackPanel Orientation='Horizontal'>
<Button x:Name='AddFruit'
Height='auto'
Width='auto'
Content='Add New Fruit 2'
Margin='0,10,0,0'
Command='{StaticResource AddFruit}' />
<Button x:Name='SaveFruit'
Height='auto'
Width='auto'
Content='Save Fruit'
Margin='100,10,0,0'
Command='{StaticResource SaveFruit}' />
</StackPanel>
</StackPanel>
</Grid>
</Window>
和我在主窗口后面的代码(添加处理程序)
using Fruits.ViewModels;
using System;
using System.Windows;
using System.Windows.Input;
namespace Fruits
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = new MainViewModel();
ViewModel.AddNewFruit("Jackfruit", "Yellow");
ViewModel.AddNewFruit("Watermelon", "ForestGreen");
ViewModel.AddNewFruit("Apple", "Red");
ViewModel.AddNewFruit("Banana", "Yellow");
ViewModel.AddNewFruit("Orange", "DeepSkyBlue");
//ViewModel.Fruits[0].IsSelected = false;
//ViewModel.Fruits[1].IsSelected = false;
ViewModel.FruitsView.Refresh();
}
public MainViewModel ViewModel { get { return DataContext as MainViewModel; } }
private void AddFruitCommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
{
ViewModel.AddNewFruit();
}
private void AddFruitCommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
e.CanExecute =
ViewModel != null
&& !String.IsNullOrWhiteSpace(ViewModel.NewFruitName)
&& !String.IsNullOrWhiteSpace(ViewModel.NewFruitColor)
;
}
private void SaveFruitCommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
{
using (var db=new FruitDbContext())
{
db.SaveChanges();
}
}
private void SaveFruitCommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
e.CanExecute = true;
}
}
}
我新添加的 dbContext:
namespace Fruits.ViewModels
{
public class FruitDbContext:DbContext
{
public DbSet<Fruit> Fruits { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionBuilder)
{
optionBuilder.UseSqlServer(@"Server = xxx; Database=Test; Integrated Security = True");
}
}
}
其他类保持不变，但我还是列出了它们:
View 模型库
namespace Fruits.ViewModels
{
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string name)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(name));
}
}
}
}
ViewModel
using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows.Data;
using System.Windows.Media;
namespace Fruits.ViewModels
{
#region MainViewModel Class
public class MainViewModel : ViewModelBase
{
public MainViewModel()
{
Fruits = new ObservableCollection<Fruit>();
}
public ICollectionView FruitsView { get; private set; }
#region ShowSelectedFruitOnly Property
private bool _showSelectedFruitOnly = true;
public bool ShowSelectedFruitOnly
{
get { return _showSelectedFruitOnly; }
set
{
if (value != _showSelectedFruitOnly)
{
_showSelectedFruitOnly = value;
FruitsView.Refresh();
OnPropertyChanged("ShowSelectedFruitOnly");
}
}
}
#endregion ShowSelectedFruitOnly Property
#region Add Methods
public void AddNewFruit()
{
Fruits.Add(new Fruit(NewFruitName, NewFruitColor));
NewFruitName = "";
NewFruitColor = "";
}
public void AddNewFruit(string name, string color)
{
Fruits.Add(new Fruit(name, color));
}
public void AddNewFruit(string name, Color color)
{
Fruits.Add(new Fruit(name, color));
}
#endregion Add Methods
#region NewFruitName Property
private String _newFruitName = default(String);
public String NewFruitName
{
get { return _newFruitName; }
set
{
if (value != _newFruitName)
{
_newFruitName = value;
OnPropertyChanged("NewFruitName");
}
}
}
#endregion NewFruitName Property
#region NewFruitColor Property
private String _newFruitColor = default(String);
public String NewFruitColor
{
get { return _newFruitColor; }
set
{
if (value != _newFruitColor)
{
_newFruitColor = value;
OnPropertyChanged("NewFruitColor");
}
}
}
#endregion NewFruitColor Property
#region Fruits Property
private static ObservableCollection<Fruit> _fruits;
public ObservableCollection<Fruit> Fruits
{
get { return _fruits; }
private set
{
if (value != _fruits)
{
_fruits = value;
FruitsView = CollectionViewSource.GetDefaultView(Fruits);
FruitsView.Filter = FruitFilterPredicate;
FruitsView.Refresh();
OnPropertyChanged("Fruits");
}
}
}
protected bool FruitFilterPredicate(Object o)
{
if (ShowSelectedFruitOnly)
{
return (o as Fruit).IsSelected;
}
return true;
}
#endregion Fruits Property
}
#endregion MainViewModel Class
}
应用程序.xaml
<Application x:Class="Fruits.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Fruits"
StartupUri="MainWindow.xaml">
<Application.Resources>
<Style x:Key="ColorSwatch"
TargetType="ContentControl">
<Setter Property="Width"
Value="24" />
<Setter Property="Height"
Value="24" />
<Setter Property="IsTabStop"
Value="false" />
<Setter Property="ContentTemplate">
<Setter.Value>
<DataTemplate>
<Rectangle HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
Stroke="Gray"
StrokeThickness="1">
<Rectangle.Fill>
<SolidColorBrush Color="{Binding}" />
</Rectangle.Fill>
</Rectangle>
</DataTemplate>
</Setter.Value>
</Setter>
</Style>
<DataTemplate x:Key='FruitTemp'>
<StackPanel Orientation='Horizontal'
Margin='5'>
<TextBlock x:Name='tbName'
Text='{Binding FruitName}'
Margin='10,0,0,0'
Width='100' />
<TextBlock x:Name='tbColor'
Text='{Binding FruitColor}'
Margin='10,0,0,0'
Width='100' />
<ContentControl Width="16"
Height="16"
Style="{StaticResource ColorSwatch}"
Content="{Binding FruitColor}" />
<!-- The problem here was you were trying to bind Checked, an event,
instead if IsChecked, a bool? property.
-->
<CheckBox x:Name='cbSelected'
Content='Selected'
Margin='10,0,0,0'
IsChecked='{Binding IsSelected}' />
</StackPanel>
</DataTemplate>
</Application.Resources>
</Application>
我的项目结构
我在 SQL Server 中的表:
CREATE TABLE [dbo].[Fruits]
(
[ID] [uniqueidentifier] NOT NULL,
[FruitName] [nvarchar](50) NULL,
[FruitColor] [nvarchar](50) NULL,
[IsSelected] [nvarchar](1) NULL,
CONSTRAINT [PK_Fruit]
PRIMARY KEY CLUSTERED ([ID] ASC)
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF,
IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON,
ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
请告知为什么消息说没有主键而它确实存在
最佳答案
此异常消息并不意味着它需要在您的数据库中定义一个主键，这意味着它需要在您的类中定义一个主键。
尽管您已尝试这样做:
这没有效果，因为 Entity Framework 会忽略只读属性。它必须:当它从数据库中检索到 Fruits 记录时，它构造一个 Fruit 对象，然后为每个映射的属性调用属性 setter 。这对只读属性永远不起作用。
您需要 Entity Framework 才能设置 ID 的值。这意味着该属性需要有一个 setter。
关于c# - 错误 : the entity type requires a primary key，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/43503424/