从ViewModel绑定的ObservableCollection不会更新视图

Question

我允许用户通过视图中的ContextMenu菜单项删除项目，我希望在视图中自动看到效果。截至目前，视图中的项目一直保持到应用程序重新启动，在这种情况下，它将不再可见。对于认为该项目已从应用程序中完全删除的用户而言，这非常令人困惑。我的问题是，我做错了什么才能解决这个问题？

App.xaml.cs

//PictureRepository is a class that gathers pictures from IsolatedStorage
public static PictureRepository PictureList
    {
        get
        {
            return PictureRepository.Instance;
        }
    }

PictureRepository.cs

#region Constants

    public const string IsolatedStoragePath = "Pictures";

    #endregion

    #region Fields

    private readonly ObservableCollection<Picture> _pictures = new ObservableCollection<Picture>();

    #endregion

    #region Properties

    public ObservableCollection<Picture> Pictures
    {
        get { return _pictures; }
    }

    #endregion

    #region Singleton Pattern

    private PictureRepository()
    {
        LoadAllPicturesFromIsolatedStorage();
    }

    public static readonly PictureRepository Instance = new PictureRepository();

    #endregion

    /// <summary>        
    /// Saves to local storage
    /// This method gets two parameters: the captured picture instance and the name of the pictures folder in the isolated storage
    /// </summary>
    /// <param name="capturedPicture"></param>
    /// <param name="directory"></param>
    public void SaveToLocalStorage(CapturedPicture capturedPicture, string directory)
    {
        //call IsolatedStorageFile.GetUserStoreForApplication to get an isolated storage file
        var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
        //Call the IsolatedStorageFile.EnsureDirectory extension method located in the Common IsolatedStorageFileExtensions class to confirm that the pictures folder exists.
        isoFile.EnsureDirectory(directory);

        //Combine the pictures folder and captured picture file name and use this path to create a new file 
        string filePath = Path.Combine(directory, capturedPicture.FileName);
        using (var fileStream = isoFile.CreateFile(filePath))
        {
            using (var writer = new BinaryWriter(fileStream))
            {
                capturedPicture.Serialize(writer);
            }
        }
    }

    /// <summary>
    /// To load all saved pictures and add them to the pictures list page
    /// </summary>
    public CapturedPicture LoadFromLocalStorage(string fileName, string directory)
    {
        //To open the file, add a call to the IsolatedStorageFile.GetUserStoreForApplication
        var isoFile = IsolatedStorageFile.GetUserStoreForApplication();

        //Combine the directory and file name
        string filePath = Path.Combine(directory, fileName);
        //use the path to open the picture file from the isolated storage by using the IsolatedStorageFile.OpenFile method
        using (var fileStream = isoFile.OpenFile(filePath, FileMode.Open, FileAccess.Read))
        {
            //create a BinaryReader instance for deserializing the CapturedPicture instance
            using (var reader = new BinaryReader(fileStream))
            {
                var capturedPicture = new CapturedPicture();
                //create a new instance of the type CapturedPicture called CapturedPicture.Deserialize to deserialize the captured picture and return it
                capturedPicture.Deserialize(reader);
                return capturedPicture;
            }
        }
    }

    /// <summary>
    /// To load all the pictures at start time
    /// </summary>
    private void LoadAllPicturesFromIsolatedStorage()
    {
        //add call to the IsolatedStorageFile.GetUserStoreForApplication to open an isolated storage file
        var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
        //Call the IsolatedStorageFile.EnsureDirectory extension method located in the Common IsolatedStorageFileExtensions class to confirm that the pictures folder exists
        isoFile.EnsureDirectory(IsolatedStoragePath);

        //Call the IsolatedStorageFile.GetFileNames using the pictures directory and *.jpg as a filter to get all saved pictures
        var pictureFiles = isoFile.GetFileNames(Path.Combine(IsolatedStoragePath, "*.jpg"));
        //var pictureFiles = isoFile.GetFileNames(Path.Combine(IsolatedStoragePath, ""));

        //Iterate through all the picture files in the list and load each using the LoadFromLocalStorage you created earlier
        foreach (var pictureFile in pictureFiles)
        {
            var picture = LoadFromLocalStorage(pictureFile, IsolatedStoragePath);
            _pictures.Add(picture);
        }
    }

MainPage.xaml.cs中

protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        //Recent is the ListBox in the view that is populated from the ObservableCollection
        if (Settings.AscendingSort.Value)
        {
            //Recent.ItemsSource = PictureRepository.Instance.Pictures.OrderBy(x => x.DateTaken);
            Recent.ItemsSource = App.PictureList.Pictures.OrderBy(x => x.DateTaken);
        }
        else
        {
            //Recent.ItemsSource = PictureRepository.Instance.Pictures.OrderByDescending(x => x.DateTaken);
            Recent.ItemsSource = App.PictureList.Pictures.OrderByDescending(x => x.DateTaken);
        }        
    }

//My attempt at deleting the item from both the View and IsolatedStorage
private void deleteContextMenuItem_Click(object sender, RoutedEventArgs e)
    {
        var listBoxItem = ((MenuItem)sender).DataContext as CapturedPicture;
        fileName = listBoxItem.FileName;

        if (fileName != null)
        {
            try
            {
                //Neither of the following remove the item from the View immediately
                App.PictureList.Pictures.Remove(listBoxItem);
                PictureRepository.Instance.Pictures.Remove(listBoxItem);


                    //To open the file, add a call to the IsolatedStorageFile.GetUserStoreForApplication
                    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
                    //Combine the directory and file name
                    string filePath = Path.Combine(PictureRepository.IsolatedStoragePath, fileName);
                    isoFile.DeleteFile(filePath);
            }
            catch
            {
                MessageBoxResult r = MessageBox.Show("There was an error deleting the image.", "Notice", MessageBoxButton.OK);
                if (r == MessageBoxResult.OK)
                    return;
            }            
        }
    }

如您所见，我正在尝试从View和IsolatedStorage中删除该项目。截至目前，从IsolatedStorage中删除是有效的，但我似乎无法让View自动更新？我必须等到应用程序重新启动并在OnNavigatedTo事件中重新填充ListBox才能看到任何更改。

Answer 1

问题是您正在为Recent.ItemSource分配IOrderedEnumerable而不是ObservableCollection。

在LoadAllPicturesFromIsolatedStorage（）中创建一个临时List，在其中添加文件中加载的数据，然后创建ObservableCollection。

PictureRepository.cs

#region Constants

public const string IsolatedStoragePath = "Pictures";

#endregion

#region Properties

public ObservableCollection<Picture> Pictures
{
    get; private set;
}

#endregion

#region Singleton Pattern

private PictureRepository()
{
    LoadAllPicturesFromIsolatedStorage();
}

public static readonly PictureRepository Instance = new PictureRepository();

#endregion

/// <summary>        
/// Saves to local storage
/// This method gets two parameters: the captured picture instance and the name of the pictures folder in the isolated storage
/// </summary>
/// <param name="capturedPicture"></param>
/// <param name="directory"></param>
public void SaveToLocalStorage(CapturedPicture capturedPicture, string directory)
{
    //call IsolatedStorageFile.GetUserStoreForApplication to get an isolated storage file
    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
    //Call the IsolatedStorageFile.EnsureDirectory extension method located in the Common IsolatedStorageFileExtensions class to confirm that the pictures folder exists.
    isoFile.EnsureDirectory(directory);

    //Combine the pictures folder and captured picture file name and use this path to create a new file 
    string filePath = Path.Combine(directory, capturedPicture.FileName);
    using (var fileStream = isoFile.CreateFile(filePath))
    {
        using (var writer = new BinaryWriter(fileStream))
        {
            capturedPicture.Serialize(writer);
        }
    }
}

/// <summary>
/// To load all saved pictures and add them to the pictures list page
/// </summary>
public CapturedPicture LoadFromLocalStorage(string fileName, string directory)
{
    //To open the file, add a call to the IsolatedStorageFile.GetUserStoreForApplication
    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();

    //Combine the directory and file name
    string filePath = Path.Combine(directory, fileName);
    //use the path to open the picture file from the isolated storage by using the IsolatedStorageFile.OpenFile method
    using (var fileStream = isoFile.OpenFile(filePath, FileMode.Open, FileAccess.Read))
    {
        //create a BinaryReader instance for deserializing the CapturedPicture instance
        using (var reader = new BinaryReader(fileStream))
        {
            var capturedPicture = new CapturedPicture();
            //create a new instance of the type CapturedPicture called CapturedPicture.Deserialize to deserialize the captured picture and return it
            capturedPicture.Deserialize(reader);
            return capturedPicture;
        }
    }
}

/// <summary>
/// To load all the pictures at start time
/// </summary>
private void LoadAllPicturesFromIsolatedStorage()
{
    //add call to the IsolatedStorageFile.GetUserStoreForApplication to open an isolated storage file
    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
    //Call the IsolatedStorageFile.EnsureDirectory extension method located in the Common IsolatedStorageFileExtensions class to confirm that the pictures folder exists
    isoFile.EnsureDirectory(IsolatedStoragePath);

    //Call the IsolatedStorageFile.GetFileNames using the pictures directory and *.jpg as a filter to get all saved pictures
    var pictureFiles = isoFile.GetFileNames(Path.Combine(IsolatedStoragePath, "*.jpg"));
    //var pictureFiles = isoFile.GetFileNames(Path.Combine(IsolatedStoragePath, ""));

    var pictures = new List<Picture>();

    //Iterate through all the picture files in the list and load each using the LoadFromLocalStorage you created earlier
    foreach (var pictureFile in pictureFiles)
    {
        var picture = LoadFromLocalStorage(pictureFile, IsolatedStoragePath);
        pictures.Add(picture);
    }

    Pictures = new ObservableCollection<Picture>(pictures.OrderBy(x => x.DateTaken));
}

在MainPage.cs上，将OnNavigatedTo方法更改为：

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    //Recent is the ListBox in the view that is populated from the ObservableCollection
    //Recent.ItemsSource = PictureRepository.Instance.Pictures.OrderBy(x => x.DateTaken);
    Recent.ItemsSource = App.PictureList.Pictures;
}