从一个VM上的列表中删除项目，然后刷新另一个VM上的列表

Question

In my project, using MVVM and C#. I have 2 ViewModels. This first loads a List and creates an Observable Collection List from it.

private ObservableCollection<Problems> _ProblemsList;
    public ObservableCollection<Problems> ProblemsList
    {
        get 
        {
            return _ProblemsList;
        }
        set
        {
            _ProblemsList = value;
            OnPropertyChanged(null);
        }
    }
    public List<Problems> Problems { get; set; }

Once the List is filled, the Observable is populated from it. I then load the observable into a gridview.

Once you select a problem on the gridview, you are taken to a new View. This View allows you to alter the data of the problem. One key field is changed, lets call it Validated (bool). Validated is changed from false to true, and once you click done, you should return to the first View, with the lists. My problem is, now that the problem has been altered, it should be removed from the list.

So in my second View's VM code, I have:

protected void DeleteFromList()
    {
        long id = selectedProblem.ID;
        ProblemsList.ProblemsList.Remove(x => x.ID == id);
    }

The first ProblemsList is the instance of the previous VM, ProblemsListingViewModel.cs I sent the instance through to the next VM, and they are filled and declared:

public InitiateWorkViewModel(CallProblems selectedProblem, ProblemsListingViewModel ProblemsList)

selectedProblem is just the problem that was selected from the list on the first View

My issue is that the observable doesn't want to refresh once I navigate back. I change the data, the Validated is changed, the problem is removed from the list in my second code input above, but it doesn't reflect when I navigate back. How do I correct this?

Basically, I want to remove the problem from the list, so that the user will know that the work has been done on that problem and they can't choose it again. I don't want to delete the whole record (from the database), just from the selectable list

If there are any further problems, please comment and I will edit the question accordingly

Answer 1

I believe that your problem is because you are calling this...:

ProblemsList.ProblemsList.Remove(x => x.ID == id);

... and expecting the UI to update itself.

Unfortunately, the ObservableCollection.Remove method does not raise the INotifyPropertyChanged.PropertyChanged event and so the UI is not updated. There are a few ways to fix this situation, as all you have to do is to raise the INotifyPropertyChanged.PropertyChanged event when you add or remove the items from the collection.

The simplest is to attach a handler to the ProblemsList.CollectionChanged event in your view model. You can then raise the INotifyPropertyChanged.PropertyChanged event each time an item is added or removed from the collection:

private void ProblemsList_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    NotifyPropertyChanged("ProblemsList");
}