How to Cancel DataGrid SelectionChange - MVVM

[hematec]

Hi Community,
i'm currently working on an App, where i have a DataGrid and also some input field like textboxes etc.
The DataGrid.ItemsSource is bound to an ObservableCollection. I also have property SelectedPerson which is bound to the DataGrid.SelectedItem and to the input fields.
Each each object in the ObservableCollection has a HasChanged property, indicating, if it was altered.
When i now edit a record (in DataGrid or in input fields) i want to avoid the user to select another Row than the currently edited in the DataGrid, before the changes of the selected record are saved or disgarded.
My attempt was to abort the selection change ind the Setter of the SelectedPerson property:

public ObservableCollection<Person> People { get; }

Person _SelectedPerson;
public Person SelectedPerson 
{ 
    get => _SelectedPerson;
    set 
    {
        // check Old is null
        if (_SelectedPerson != null)
        {
            // check if changed & try to save
            if (_SelectedPerson.HasChanged)
            {
                // error -> abort selection change
                Task.Run(() =>
                {
                    Task.Delay(500).Wait();
                    Dispatcher.UIThread.InvokeAsync(() => this.RaisePropertyChanged(nameof(SelectedPerson)), DispatcherPriority.Render);
                    //this.RaisePropertyChanged(nameof(SelectedPerson));
                });

                // and go back
                return;
            }
        }

        // all is fine, Change property
        this.RaiseAndSetIfChanged(ref _SelectedPerson, value); 
    }
}

In the input fileds, the SelectedPerson stays as expected unchanged, but the DataGrid doesn't care at all and changes its selection.

What would be the correct approach to get the expected behavior?

[msneijders]

Are you using the cell/row editing functionality of DataGrid?

ie:

DataGrid dg;
dg.IsReadOnly = false;

dg.RowEditEnding += (s, e) =>
{
    e.Cancel = (e.Row.DataContext as MyViewModelItem).HasChangedButNotSaved;
}

I think editing modus influences selecting. You can also use CellEditEnding.

[hematec]

Hi, thanks a lot for this hint!

I added you code to my sample application, but unfortunately this only works partially.
When i first edit a row in grid and then try to change the selected row, it could not change.
When is save the changes and then edit the record in the input fields, i could not change the row.
But when i save the changes, select another row and directly start editing in the input fields, i could change the row

2025-01-15.13-59-59.mp4

[msneijders]

But when i save the changes, select another row and directly start editing in the input fields, i could change the row

Probably because the datagrid is not in editing modus here. I see you selecting the 3rd row. And then change value in a textbox outside of the datagrid. Editing that textbox will not set the datagrid into edit modus, and so event RowEditEnding will not fire (debug or trace that handler to check).

You can set the datagrid into edit modus manually using BeginEdit() (and probably manually end editing, CommitEdit() or CancelEdit()).

[hematec]

Hi msneijders,

yes, this was also my thought and i could confirm it.

Adding those 2 handler did the job

dgPersons.RowEditEnding += (s, e) =>
{
    e.Cancel = (e.Row.DataContext as Person).HasChanged;
};

dgPersons.GotFocus += (s, e) =>
{
    (s as DataGrid).BeginEdit();
};

Thx a lot for your help!!