Question

我正在与Caliburn Micro学习WPF。我已经阅读了很多次文档，甚至正在关注Timcorey在YouTube上的教程。我一定没有正确指定/初始化一些东西。

通常我将对象指定为X obj = new X（）;但是在这种情况下，eventaggregator不喜欢它。我确实通过将events.subscribe行更改为：

来使代码得以运行。

if (_events != null) _events.Subscribe(this)

但是在运行时，即使设置了断点，代码也永远不会到达此行。删除所有eventaggregator代码后，我可以运行并触发事件。我似乎无法发布和订阅它。

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using PropertyChanged;
using Caliburn.Micro;

using ERP101.EventModels;
using ERP101.ViewModels;

namespace ERP101.ViewModels
{
    [AddINotifyPropertyChangedInterface]
    public class ShellViewModel : Conductor<object>,IHandle<LoginEvent>
    {
        private IEventAggregator _events;
        private StartPageViewModel _startPVM;
        private SimpleContainer _container;

        public ShellViewModel(IEventAggregator events,StartPageViewModel startPVM,SimpleContainer container)
        {
            _events = events;
            _events.Subscribe(this); //null reference error here
            _startPVM = startPVM;
            _container = container;

             ActivateItem(_container.GetInstance<LoginViewModel>());

        }

        public void Handle(LoginEvent message)
        {
            ActivateItem(_startPVM);
        }
    }
}```

Answer 1

Thanks Amy, So I went again back to the tutorials and I found my issue in the container code.


        protected override void Configure()
        {
            _container.Instance(_container);
            _container
                .Singleton<IWindowManager, WindowManager>()
                .Singleton<IEventAggregator, EventAggregator>();

            GetType().Assembly.GetTypes()
                .Where(type => type.IsClass)
                .Where(type => type.Name.EndsWith("ViewModel"))
                .ToList()
                .ForEach(viewModelType => _container.RegisterPerRequest(viewModelType, viewModelType.ToString(), viewModelType));
        }

.Singleton<EventAggregator, EventAggregator>(); - this line is incorrect, the corrected line is in code above. The first had to be an interface type.

为什么我的event.Subscribe（）行返回空引用错误？

1 个答案: