Listview將不會每次更新時，我正在加載JSON文件

Question

我正在使用MVVM模式製作Windows商店應用程序。當我從JSON文件加載字典並將其綁定到列表視圖時，每當我切換視圖時它都不會更新。有時候，listview正在更新，有時候不會。有什麼出錯的建議？

類KundePersistency

public static async Task<List<Kunde>> LoadKunderFromJsonAsync() 
{ 
    string kundeJsonString = await DeserializekunderFileAsync(JsonFileKunder); 
    if (kundeJsonString != null) 
     return (List<Kunde>)JsonConvert.DeserializeObject(kundeJsonString, typeof(List<Kunde>)); 
    return null; 
} 

private static async Task<string> DeserializekunderFileAsync(string fileName) 
{ 
    try 
    { 
     StorageFile localFile = await ApplicationData.Current.LocalFolder.GetFileAsync(fileName); 
     return await FileIO.ReadTextAsync(localFile); 
    } 
    catch (FileNotFoundException) 
    { 
     return null; 
    } 
} 

類BookingSystem（視圖模型）

private async void LoadKunder() 
{ 
    _id = 1; 
    var loadedKunder = await KundePersistency.LoadKunderFromJsonAsync(); 

    if (loadedKunder != null) 
    { 
     KundeRegister.KundeMedId.Clear(); 
     foreach (var kunde in loadedKunder) 
     { 
      KundeRegister.KundeMedId.Add(_id++, kunde); 

     } 
    } 
} 

類KundeRegister（型號）

public class KundeRegister : INotifyPropertyChanged 
{ 
    public Dictionary<int, Kunde> KundeMedId { get; set; } 


public KundeRegister() 
{ 
    KundeMedId = new Dictionary<int, Kunde>();   
    KundeMedId.Add(Kunde.Id,new Kunde("bob","bob","bob","bobbobbo","bob","bob")); 
    KundeMedId.Add(Kunde.Id, new Kunde("bob", "bob", "bob", "bobbobbo", "bob", "bob")); 

} 

public void AddKunde(string username, string password,string adresse,string email, string name, string tlf) 
{ 
    KundeMedId.Add(Kunde.Id, new Kunde(adresse, email, name, tlf, username, password)); 
    OnPropertyChanged(); 
} 


public event PropertyChangedEventHandler PropertyChanged; 

[NotifyPropertyChangedInvocator] 
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) 
    { 
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); 
    } 

} 

Answer 1

您需要爲您的用戶ObeservableCollection作爲字典不執行INotifyPropertyChanged默認

private ObservableCollection<NavigationItem> _loadedKunder ; 
    public ObservableCollection<NavigationItem> loadedKunder 
    { 
     get { return _loadedKunder ; } 
     set 
     { 
      if (value != _loadedKunder) 
      { 
       _loadedKunder = value; 
       NotifyPropertyChanged("loadedKunder"); 
      } 
     } 
    }