我使用了MVVM Light工具包，当我在ViewModelLocator中加载ViewModel实例时，我得到了异常。mscorlib.ni.dll中发生了'System.Reflection.TargetInvocationException'类型的异常，但未在用户代码中处理。我搜索了很多，但找不到解决方案
我的ViewModelLocator代码:
/*
In App.xaml:
<Application.Resources>
<vm:ViewModelLocator xmlns:vm="clr-namespace:ToDoList"
x:Key="Locator" />
</Application.Resources>
In the View:
DataContext="{Binding Source={StaticResource Locator}, Path=ViewModelName}"
You can also use Blend to do all this with the tool's support.
See http://www.galasoft.ch/mvvm
*/
using Cimbalino.Phone.Toolkit.Services;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Ioc;
using GalaSoft.MvvmLight.Messaging;
using Microsoft.Practices.ServiceLocation;
using System.Windows;
namespace ToDoList.ViewModel
{
/// <summary>
/// This class contains static references to all the view models in the
/// application and provides an entry point for the bindings.
/// </summary>
public class ViewModelLocator
{
/// <summary>
/// Initializes a new instance of the ViewModelLocator class.
/// </summary>
public ViewModelLocator()
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
////if (ViewModelBase.IsInDesignModeStatic)
////{
//// // Create design time view services and models
//// SimpleIoc.Default.Register<IDataService, DesignDataService>();
////}
////else
////{
//// // Create run time view services and models
//// SimpleIoc.Default.Register<IDataService, DataService>();
////}
if (!SimpleIoc.Default.IsRegistered<IMarketplaceReviewService>())
{
SimpleIoc.Default.Register<IMarketplaceReviewService, MarketplaceReviewService>();
}
SimpleIoc.Default.Register<ToDoViewModel>();
}
public ToDoViewModel ToDo
{
get
{
return ServiceLocator.Current.GetInstance<ToDoViewModel>();
}
}
public static void Cleanup()
{
// TODO Clear the ViewModels
var viewModelLocator = (ViewModelLocator)Application.Current.Resources["Locator"];
viewModelLocator.ToDo.Cleanup();
Messenger.Reset();
}
}
}
我的ToDoViewModel:
using Cimbalino.Phone.Toolkit.Services;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using ToDoList.Models;
namespace ToDoList.ViewModel
{
public class ToDoViewModel : ViewModelBase
{
private readonly IMarketplaceReviewService _marketplaceReviewService;
public ICommand DeleteCommand { get; private set; }
public ICommand AddCommand { get; set; }
public ICommand RateCommand { get; private set; }
public string Text { get; set; }
// LINQ to SQL data context for the local database.
private ToDoDataContext toDoDB;
// Class constructor, create the data context object.
public ToDoViewModel(string toDoDBConnectionString, IMarketplaceReviewService marketplaceReviewService)
{
_marketplaceReviewService = marketplaceReviewService;
toDoDB = new ToDoDataContext(toDoDBConnectionString);
DeleteCommand = new RelayCommand<ToDoItem>(DeleteToDoItem);
AddCommand = new RelayCommand(Add);
LoadCollectionsFromDatabase();
RateCommand = new RelayCommand(Rate);
}
private void Rate()
{
_marketplaceReviewService.Show();
}
private void Delete(ToDoItem newToDoItem)
{
//ToDoItem newToDoItem = obj as ToDoItem;
DeleteToDoItem(newToDoItem);
}
private void Add()
{
ToDoItem newToDoItem = new ToDoItem
{
ItemName = this.Text,
};
AddToDoItem(newToDoItem);
}
//
// TODO: Add collections, list, and methods here.
//
// Write changes in the data context to the database.
public void SaveChangesToDB()
{
toDoDB.SubmitChanges();
}
// All to-do items.
private ObservableCollection<ToDoItem> _allToDoItems;
public ObservableCollection<ToDoItem> AllToDoItems
{
get { return _allToDoItems; }
set
{
_allToDoItems = value;
NotifyPropertyChanged("AllToDoItems");
}
}
public void LoadCollectionsFromDatabase()
{
// Specify the query for all to-do items in the database.
var toDoItemsInDB = from ToDoItem todo in toDoDB.Items
select todo;
// Query the database and load all to-do items.
AllToDoItems = new ObservableCollection<ToDoItem>(toDoItemsInDB);
// Specify the query for all categories in the database.
}
// Add a to-do item to the database and collections.
public void AddToDoItem(ToDoItem newToDoItem)
{
// Add a to-do item to the data context.
toDoDB.Items.InsertOnSubmit(newToDoItem);
// Save changes to the database.
toDoDB.SubmitChanges();
// Add a to-do item to the "all" observable collection.
AllToDoItems.Add(newToDoItem);
}
// Remove a to-do task item from the database and collections.
public void DeleteToDoItem(ToDoItem toDoForDelete)
{
// Remove the to-do item from the "all" observable collection.
AllToDoItems.Remove(toDoForDelete);
// Remove the to-do item from the data context.
toDoDB.Items.DeleteOnSubmit(toDoForDelete);
// Save changes to the database.
toDoDB.SubmitChanges();
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
// Used to notify the app that a property has changed.
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
}
异常(exception)发生在
最佳答案
实际上，您的ViewModelLocator无法创建 ToDoViewmodel 的实例，因为您的TodoViewmodel需要两个参数，一个是IMarketplaceReviewService类型，另一个是字符串toDoDbConnectionString。
注意:-IMarketplaceReviewService类型参数来自于您已经注册的ViewmodelLocator，但是您的Second参数toDoDbConnectionString并非来自任何地方，因此ToDoViewModel不会被实例化。
第一个解决方案:-这是快速的法律解决方法(因为我不知道您的连接字符串将要更改还是保持不变)。因此，像这样更改您的TodoViewModel构造函数:
public ToDoViewModel(IMarketplaceReviewService marketplaceReviewService)
{
// Save your connection string somewhere in Constant Class
// Use that constants directly here.
_toDoDbConnectionString = "Your Connection string";
...
}
第二个解决方案:-您可以创建
Setting - ISetting(类接口(interface))对，并通过与传递IMarketplaceReviewService相似的方式传递它，并在ViewModelLocator中注册它。希望对您有所帮助:)
关于c# - 'System.Reflection.TargetInvocationException'(在MVVM中)，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/28263460/