c# - 我的 ASP.NET Core MVVM Blazor 应用程序的依赖注入无法正常工作

问题描述

我在尝试应用依赖注入时遇到了麻烦。经过大量研究并查看 YouTube 上的各种视频和 Stack Overflow 上的答案后，我的 ITaskRepository 不断返回 null 而不是我的存储库的实例。查看我的代码，似乎我已经添加了所有正确的东西来使依赖注入工作。

我的基础存储库界面

using portfolio_backend.Data.Base;
using System.Collections.Generic;

namespace portfolio_backend.Business.Repositories.Base
{
    public interface IBaseRepository<TEntity> where TEntity : BaseModel
    {
        void Add(TEntity model);
        void Delete(TEntity model);
        bool Exists(int Id);
        TEntity Get(int Id);
        IEnumerable<TEntity> GetAll();
        void Update(int Id, TEntity model);
    }
}

我的 BaseRepository 类


using Microsoft.EntityFrameworkCore.Internal;
using portfolio_backend.Data;
using portfolio_backend.Data.Base;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace portfolio_backend.Business.Repositories.Base
{
    public class BaseRepository<TEntity> : IBaseRepository<TEntity> where TEntity : BaseModel
    {
        protected PortfolioContext _context;

        public BaseRepository(PortfolioContext context)
        {
            _context = context;
        }

        public void Add(TEntity model)
        {
            if (!Exists(model.Id))
            {
                _context.Set<TEntity>().Add(model);
                _context.SaveChanges();
            }
        }

        public void Delete(TEntity model)
        {
            if (Exists(model.Id))
            {
                _context.Set<TEntity>().Remove(model);
                _context.SaveChanges();
            }
        }

        public bool Exists(int Id)
        {
            return _context.Set<TEntity>().Any(model => model.Id == Id);
        }

        public TEntity Get(int Id)
        {
           return _context.Set<TEntity>().FirstOrDefault(model => model.Id == Id);
        }

        public IEnumerable<TEntity> GetAll()
        {
            return _context.Set<TEntity>().ToList();
        }

        public void Update(int Id, TEntity model)
        {
            var modelToFind = Get(Id);
            _context.Set<TEntity>().Update(modelToFind);
            _context.SaveChanges();
        }
    }
}

我的 ITaskRepository 接口

using portfolio_backend.Business.Repositories.Base;
using portfolio_backend.Data;
using System.Collections.Generic;

namespace portfolio_backend.Business.Repositories
{
    public interface ITaskRepository : IBaseRepository<Task>
    {
        IEnumerable<Task> GetTaskByProjects(int ProjectId);
    }
}

任务存储库实现

using portfolio_backend.Business.Repositories.Base;
using portfolio_backend.Data;
using System.Collections.Generic;
using System.Linq;

namespace portfolio_backend.Business.Repositories
{
    public class TaskRepository : BaseRepository<Task>, ITaskRepository
    {
        public TaskRepository(PortfolioContext context) : base(context)
        {
        }

        public IEnumerable<Task> GetTaskByProjects(int ProjectId)
        {
            return _context.Tasks.OrderByDescending(task => task.Project.Id == ProjectId).ToList();
        }
    }
}

我的创业班：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using portfolio_backend.Business.Repositories.Base;
using portfolio_backend.Business.Repositories;
using portfolio_backend.Data;
using Blazorise;
using Blazorise.Bootstrap;
using Blazorise.Icons.FontAwesome;

namespace portfolio_backend.Presentation
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<PortfolioContext>(options => 
                options.UseMySQL(Configuration.GetConnectionString("portfolio")));

            services.AddScoped(typeof(IBaseRepository<>), typeof(BaseRepository<>));
            services.AddScoped<ITaskRepository, TaskRepository>();

            services.AddBlazorise(options =>{
                options.ChangeTextOnKeyPress = true;})
                      .AddBootstrapProviders()
                      .AddFontAwesomeIcons();

            services.AddRazorPages();
            services.AddServerSideBlazor();
            
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.ApplicationServices
                  .UseBootstrapProviders()
                  .UseFontAwesomeIcons();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapBlazorHub();
                endpoints.MapFallbackToPage("/_Host");
            });
        }
    }
}

我正在尝试对以下两个类应用依赖注入：

Tasks.razor.cs（Blazor 组件的代码隐藏）

using portfolio_backend.Business;
using portfolio_backend.Business.Repositories;

namespace portfolio_backend.Presentation.Pages
{
    public partial class Tasks
    {
        private ITaskRepository _taskRepository;
        private TaskViewModel _taskViewModel => new TaskViewModel(_taskRepository);

        protected override void OnInitialized()
        {
             _taskViewModel.SeedTasks();
        }

    }
}

以及该组件的视图模型

using portfolio_backend.Business.Repositories;
using portfolio_backend.Data;
using System.Collections.Generic;

namespace portfolio_backend.Business
{
    public class TaskViewModel
    {
  
        private ITaskRepository _taskRepository {get; set;}
        private List<Task> _allTasks;

        public TaskViewModel(ITaskRepository repository)
        {
            _taskRepository = repository;
        }

        public List<Task> AllTasks
        {
            get => _allTasks;
            set => _taskRepository.GetAll();
        }

        public void SeedTasks() 
        {
            _taskRepository.Add( new Task { Description = "Task 1"} );
            _taskRepository.Add(new Task { Description = "Task 2" });
            _taskRepository.Add(new Task { Description = "Task 3" });
        }

    }
}

_taskRepository 总是返回 null，这是出现的错误消息：

System.NullReferenceException: 'Object reference not set to an instance of an object.'

我能做些什么来解决这个问题？或者在这种情况下如何更好地应用 DI？

更新：

我根据评论中建议的解决方案之一进行了以下更改：

using portfolio_backend.Business;
using portfolio_backend.Business.Repositories;

namespace portfolio_backend.Presentation.Pages
{
    public partial class Tasks
    {
        private ITaskRepository _taskRepository;
        private TaskViewModel _taskViewModel;

        public Tasks(ITaskRepository repository)
        {
            _taskRepository = repository;
            _taskViewModel = new TaskViewModel(_taskRepository);
        }

        protected override void OnInitialized()
        {
             _taskViewModel.SeedTasks();
        }

    }
}

这将触发以下错误：

MissingMethodException: No parameterless constructor defined for type 'portfolio_backend.Presentation.Pages.Tasks'.

正如错误提示的那样，我添加了一个额外的无参数构造函数

using portfolio_backend.Business;
using portfolio_backend.Business.Repositories;

namespace portfolio_backend.Presentation.Pages
{
    public partial class Tasks
    {
        private ITaskRepository _taskRepository;
        private TaskViewModel _taskViewModel;

        public Tasks()
        {
        }

        public Tasks(ITaskRepository repository)
        {
            _taskRepository = repository;
            _taskViewModel = new TaskViewModel(_taskRepository);
        }

        protected override void OnInitialized()
        {
             _taskViewModel.SeedTasks();
        }

    }
}

上面的更改在 taskRepository 为空时产生了相同的问题。

标签： c#asp.net-coredependency-injectionblazorrepository-pattern

c# - 我的 ASP.NET Core MVVM Blazor 应用程序的依赖注入无法正常工作

问题描述

解决方案

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