可观察到的集合仅删除项目一次，再次尝试时不起作用-Windows Phone 8-C＃

Question

I am writing my first application for WP8 platform in C#. I implemented three datatypes namely locationModel which has locationGroups. Each locationGroup has a ObservableCollection of type locationData.

locationData has two double types for latitude and longitude and a title string.

I used a textblock inside a stackpanel to show the locationData element's title, where the lat long are hidden to user. There is a context menu on each of this textblock element which enable the user to delete the respective locationData. When I open the app and delete any item, it succesfully does and updates the view too. But when I do it for another item it just doesnt work. I cannot delete more than one items for each time I open the app.

I used breakpoints to see where the problem is. the selected locationData is succesfully passed to the App.ViewModel.LocationModel.Items.Remove(). But it just that they are not deleted from the observable collection. I even tried to see the index of the locationData in observable collection and use RemoveAt method. Even it doesnt work. I did a lot of research to find the problem, but no one seems to face the same problem as me. I referred to msdn article on how to implement inotifypropertychanged to update the collection. But its too complex for me to understand that.

I dont really understand why the observable collection delete the item for the second time even though if I pass the index of that item. And my usage of breakpoints showed me that the data is not even null.

So kindly tell me what is causing this problem and how do I overcome it so that I can implement my own workaround and not face this issue again. I can show you the code if you want me to. Thanks.

CODE: Adding an item

private void SaveLocationData(LocationData locationData)
    {
        IsolatedStorageSettings appSettings = IsolatedStorageSettings.ApplicationSettings;

        try
        {
            App.ViewModel.Custom.Items.Add(locationData);
            var data = JsonConvert.SerializeObject(App.ViewModel.Custom);

            appSettings[LocationModel.CustomKey] = data;
            appSettings.Save();

            //Notify that data is changed
            App.ViewModel.LoadData();
            NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.RelativeOrAbsolute));
        }
        catch(IsolatedStorageException ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

Deleting item:

private void DeleteLocationData(LocationData locationData)
    {
        IsolatedStorageSettings appSettings = IsolatedStorageSettings.ApplicationSettings;

        try
        {
            App.ViewModel.Custom.Items.Remove(locationData);
            var data = JsonConvert.SerializeObject(App.ViewModel.Custom);

            appSettings[LocationModel.CustomKey] = data;
            appSettings.Save();

            //Notify that data is changed
            App.ViewModel.LoadData();
            NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.RelativeOrAbsolute));
        }

        catch (IsolatedStorageException ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

One more thing that I want to say is, whenever I add a locationData to the collection, it updates automatically. Because adding is done on another page and when the mainpage.xaml loads(in which the observable collection data is), it updates automatically because of the code in OnNavigatedTo method.

protected override void OnNavigatedTo(NavigationEventArgs e)
    {

        if (!App.ViewModel.IsDataLoaded)
        {
            App.ViewModel.LoadData();
        }

    }

And LoadData method is :

public void LoadData()
    {

        Custom = LoadCustomLocations();
        IsDataLoaded = true;

    }

    private LocationGroup LoadCustomLocations()
    {
        string dataFromAppSettings;
        LocationGroup data;

        if (IsolatedStorageSettings.ApplicationSettings.TryGetValue(CustomKey, out dataFromAppSettings))
        {
            data = JsonConvert.DeserializeObject<LocationGroup>(dataFromAppSettings);
        }
        else
        { 
            data = new LocationGroup();
        }

        return data;
    }

So, can anyone help ?

Answer 1

In the case you described on your comment I think you set the DataContext to your Items. When you create a new Items-List the DataContext will be lost. So you have to reset the DataContext to the new loaded Items-List