[英]Using DbContext with dependency injection
I building WPF application in MVVM architecture.我在 MVVM 架构中构建 WPF 应用程序。 Pressing button should give me data from database on DataGrid.按下按钮应该给我 DataGrid 数据库中的数据。 App correctly build and I can start it but when I press button I get "Object reference[...]" and information about dbContext was null.应用程序正确构建并且我可以启动它但是当我按下按钮时我得到“对象引用[...]”并且关于 dbContext 的信息是 null。
Below some code:下面是一些代码:
AuctionDbContext.cs AuctionDbContext.cs
public class AuctionDbContext: DbContext
{
public AuctionDbContext(DbContextOptions<AuctionDbContext> options): base(options)
{
/* Database.EnsureCreated();*/
}
public DbSet<Auction> Auctions { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
}
App.cs应用程序
public partial class App : Application
{
private ServiceProvider serviceProvider;
private DbCreator dbCreator = new DbCreator();
public App()
{
ServiceCollection services = new ServiceCollection();
services.AddDbContext<AuctionDbContext>(option =>
{
option.UseSqlite("Data Source = " + DbCreator.DATABASE_FILE_PATH);
});
services.AddSingleton<MainWindow>();
serviceProvider = services.BuildServiceProvider();
}
private void OnStartup(object sender, StartupEventArgs e)
{
dbCreator.createDbFile();
dbCreator.createConnectionToDatabase();
dbCreator.createTable();
dbCreator.fillTable();
var mainWindow = serviceProvider.GetService<MainWindow>();
mainWindow.Show();
}
}
}
MainWindow.cs主窗口.cs
public partial class MainWindow : Window
{
AuctionDbContext dbContext;
public MainWindow()
{
InitializeComponent();
}
private void MarketMenu_Clicked(object sender, RoutedEventArgs e)
{
DataContext = new MarketViewModel(dbContext);
}
}
MarketViewModel.cs MarketViewModel.cs
public class MarketViewModel
{
AuctionDbContext dbContext;
MarketView marketView = new MarketView();
public MarketViewModel(AuctionDbContext dbContext)
{
this.dbContext = dbContext;
GetAuctions();
}
private void GetAuctions()
{
marketView.AuctionDG.ItemsSource = dbContext.Auctions.ToList(); /* Here I got error */
}
}
}
I used this doc and I do not see any mistake:( https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext我使用了这个文档,我没有看到任何错误:( https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext
Before, when I had all in mainWindow class, everything was ok but that was PoC.之前,当我在 mainWindow class 中拥有所有内容时,一切正常,但那是 PoC。 Something went wrong, when I refactor project to MVVM.当我将项目重构为 MVVM 时出了点问题。 I spent a couple of hours looking for a solution but without success.我花了几个小时寻找解决方案但没有成功。
If it will help, here's my repo on GitHub https://github.com/BElluu/EUTool .如果有帮助,这是我在 GitHub https://github.com/BElluu/EUTool上的回购协议。 Look at branch: 1-refactor-to-mvvm coz of master is outdated yet:)看看分支:master的 1-refactor-to-mvvm coz 已经过时了:)
You don't seem to initialize the dbContext
field in the MainWindow
:您似乎没有在MainWindow
中初始化dbContext
字段:
public partial class MainWindow : Window
{
AuctionDbContext dbContext;
public MainWindow(AuctionDbContext dbContext)
{
this.dbContext = dbContext;
InitializeComponent();
}
private void MarketMenu_Clicked(object sender, RoutedEventArgs e)
{
DataContext = new MarketViewModel(dbContext);
}
}
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