值不会落在MVVM的预期范围内

Question

我试图将2个项目绑定到xaml页面。一个是可观察的服务集合，另一个是专家项目的实例。得到错误发生了类型'System.ArgumentException'的第一次机会异常myapp.Client.DLL 当我尝试为专家项目提升INotifyProperty时。

SummaryPage.xaml

//为简洁专家省略了一些字段

<TextBlock Text="Full Name" HorizontalAlignment="Left"/>
<TextBlock Text="{Binding Expert.name,Mode=TwoWay}" Grid.Column="1" HorizontalAlignment="Center"/>
<TextBlock Text="Age" Grid.Row="1" HorizontalAlignment="Left"/>
<TextBlock Text="{Binding Expert.age}" Grid.Row="1" Grid.Column="1" HorizontalAlignment="Left"/>
<TextBlock Text="National ID:" Grid.Row="2" HorizontalAlignment="Left"/>

//可观察列表服务

 <ListView ItemsSource="{Binding Services}" 
          IsItemClickEnabled="False"  
          ScrollViewer.VerticalScrollMode="Enabled"
          ScrollViewer.VerticalScrollBarVisibility="Visible"
          TabIndex="1" Header="Service Request">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition/>
                                <ColumnDefinition/>
                            </Grid.ColumnDefinitions>
         <TextBlock Text="{Binding Name}" HorizontalAlignment="Left"/>
         <TextBlock Text="{Binding Cost}" Grid.Column="1" HorizontalAlignment="Center"/>
                        </Grid>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>

SummaryPageViewModel.cs

public class SummaryPageViewModel : ViewModel, ISummaryPageViewModel
    {
        public ICommand ConfirmCommand { get; private set; }
        public ExpertItem Expert { get { return this.GetValue<ExpertItem>(); } set { this.SetValue(value); } }
        public ObservableCollection<ServiceItem> Services { get { return this.GetValue<ObservableCollection<ServiceItem>>(); } set { this.SetValue(value); } }

     public SummaryPageViewModel()
        {
        }

        public override void Initialize(IViewModelHost host)
        {
            base.Initialize(host);
            // setup...
            this.Services = new ObservableCollection<ServiceItem>();
            this.Expert = new ExpertItem();                     

            this.ConfirmCommand = new DelegateCommand((args) => GetSelected(args as CommandExecutionContext));
        }
 public override async void Activated(object args)
    {
        base.Activated(args);
        var conn = Myapp.GetSystemDatabase();
        using (this.EnterBusy())
            {
             IEnumerable<ServiceItem> servs = await conn.Table<ServiceItem>().ToListAsync();
                foreach (ServiceItem s in servs)
                    this.Services.Add(s);
 IEnumerable<ExpertItem> exps = await ExpertItem.GetAllFromCacheAsync();
                 this.Expert =  await conn.Table<ExpertItem>().Where(v => v.NativeId == 3).FirstOrDefaultAsync();               
            }
        }

ModelItem.cs

public abstract class ModelItem : INotifyPropertyChanged
    {
        private Dictionary<string, object> Values { get; set; }

        protected ModelItem()
        {
            this.Values = new Dictionary<string, object>();
        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected T Get

Value<T>([CallerMemberName] string name = null)
            {
                if (this.Values.ContainsKey(name))
                    return (T)this.Values[name];
                else
                    return default(T);
            }

            protected void SetValue(object value, [CallerMemberName] string name = null)
            {
                // set...
                this.Values[name] = value;

                // notify...
                this.OnPropertyChanged(new PropertyChangedEventArgs(name));
            }

            protected void OnPropertyChanged([CallerMemberName] string name = null)
            {
                this.OnPropertyChanged(new PropertyChangedEventArgs(name));
            }

            protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
            {
                if (this.PropertyChanged != null)
                    this.PropertyChanged(this, e);//error raised here e- property name expert.Value does not fall in expected range
            }
        }

ExpertItem.cs

//code omitted for brevity
 public class ExpertItem : ModelItem 
    {
        public int Id { get; set; }
        public int NativeId { get { return this.GetValue<int>(); } set { this.SetValue(value); } }

        public string name { get { return this.GetValue<string>(); } set { this.SetValue(value); } }

        public int age { get { return this.GetValue<int>(); } set { this.SetValue(value); } }
        public string email { get { return this.GetValue<string>(); } set { this.SetValue(value); } }
}

栈跟踪

at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e) 
at MFundi.Client.ModelItem.OnPropertyChanged(PropertyChangedEventArgs e) 
at MFundi.Client.ModelItem.SetValue(Object value, String name) 
at MFundi.Client.SummaryPageViewModel.set_Expert(ExpertItem value) 
at MFundi.Client.SummaryPageViewModel.<Activated>d__b.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- 
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<ThrowAsync>b__3(Object state)