当 observablecollection ItemSource 更改 WPF 时，通过 MVVM 以编程方式关注行中的特定单元格

Question

I'm trying to set the focus on a specific cell in a row in my DataGrid. The datagrid is bound to an observable collection of X. When I hit a specific button, it causes a new X to be inserted into the observable collection, but there is no focus on the datagrid's side of things and I want to focus the cursor so you can type in the newly created row (a specific cell in the row). Is this possible going the MVVM route? My VM has the observable collection, so not too sure where to go from here...

Answer 1

I came up with a simple example

1) MVVM helper classes (for visibility):

public class NotifyPropertyChanged : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged([CallerMemberName]string propertyName = null)
        => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public class RelayCommand : ICommand
{
    private readonly Action<object> _execute;
    private readonly Func<object, bool> _canExecute;

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
    {
        _execute = execute;
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter) => _canExecute == null || _canExecute(parameter);
    public void Execute(object parameter) => _execute(parameter);
}

2) Markup

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="30"/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <StackPanel Orientation="Horizontal" Margin="5">
        <Button Content="Add row" Command="{Binding AddRowCommand}"/>
    </StackPanel>
    <DataGrid ItemsSource="{Binding ItemsList}" Grid.Row="1" AutoGenerateColumns="False" LoadingRow="DataGrid_LoadingRow" CanUserAddRows="False" >
        <DataGrid.Columns>
            <DataGridTextColumn Header="Column 1" Binding="{Binding Column1}"/>
            <DataGridTextColumn Header="Column 2" Binding="{Binding Column2}"/>
        </DataGrid.Columns>
    </DataGrid>
</Grid>

3) ViewModel and data

public class MainViewModel : NotifyPropertyChanged
{
    private ObservableCollection<DataItem> _itemsList;
    private ICommand _addRowCommand;
    public ObservableCollection<DataItem> ItemsList
    {
        get => _itemsList;
        set
        {
            _itemsList = value;
            OnPropertyChanged();
        }
    }
    public ICommand AddRowCommand => _addRowCommand ?? (_addRowCommand = new RelayCommand(parameter =>
    {
        ItemsList.Add(new DataItem());
    }));
    public MainViewModel()
    {
        ItemsList = new ObservableCollection<DataItem>
        {
            new DataItem { Column1 = "aaa", Column2 = "bbb" },
            new DataItem { Column1 = "ccc", Column2 = "ddd" }
        };
    }
}

public class DataItem : NotifyPropertyChanged
{
    private string _column1;
    private string _column2;

    public string Column1
    {
        get => _column1;
        set
        {
            _column1 = value;
            OnPropertyChanged();
        }
    }
    public string Column2
    {
        get => _column2;
        set
        {
            _column2 = value;
            OnPropertyChanged();
        }
    }
}

4) And the Event handler in code-behind class

private void DataGrid_LoadingRow(object sender, DataGridRowEventArgs e)
{
    DataGrid dataGrid = sender as DataGrid;

    // condition avoids execution when DataGrid initially loading
    // and case when DataGrid adding an empty row if UserCanAddRows is enabled
    if (dataGrid.IsLoaded && e.Row.Item is DataItem)
    {
        dataGrid.Focus(); // moving focus from button to DataGrid
        dataGrid.SelectedIndex = e.Row.GetIndex(); // highlighting current row as selected, just a visual thing, you may remove it
        dataGrid.CurrentCell = new DataGridCellInfo(e.Row.Item, dataGrid.Columns[0]); // set current cell
        Dispatcher.BeginInvoke((Action)(() =>
        {
            dataGrid.BeginEdit(); // to avoid focus issue I'm running this through Dispatcher asynchronously
        }));
    }
}

This doesn't break MVVM because Event handler not interacting with data but only check its type. Maybe there's a more safe way to check if it's not a NewItemPlaceholder in the e.Row.Item . Or you may remove type checking in case CanUserAddRows is set to false.