更改WPF DataGrid中其他ComboBox的值

Question

Here is my problem. I am pulling in data from a webserver (with a web request) into a ObservableCollection

ObservableCollection<TestData> fillData = new ObservableCollection<TestData>();

From there I fill a data grid with the information. One of those fields within that data grid is a combobox. Depending on the amount of data that get's pulled in you can have several lines with data.

 <DataGridTemplateColumn Header="Role">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Role}">
                            </TextBlock>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                    <DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <ComboBox ItemsSource="{StaticResource RoleList}" SelectedItem="{Binding Role}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellEditingTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>

The combobox can have 3 values. Primary, Secondary and Loaner. When you change the value inside of the combobox then the ObservableCollection is updated like it should. The problem lies that you can only have one Primary selected, so when you change the value of one of the combo-boxes to primary then I have 2 or more primaries in my ObservableCollection.

I am looking for a way that when you change a value of one of the combo-boxes to primary the other values that are also primary in the datagrid (combo-boxes) will be changed to secondary. So that you only have one primary at the time. I am a bit lost, hope that anybody can give me some tips. :)

Answer 1

You should look into eventing.

When the Role property is changed, or when any of the Combobox SelectedValue's change, you need to loop through the list and make any changes needed.

You could add an eventhandler for the combobox SelectionChanged event and do the check then Or perhaps the ObservableCollection.CollectionChanged for the datasource of the grid.

Answer 2

Here's an example of how you might do that.

In any given collection of row items (whatever you call the class in your ObservableCollection), all the items in the collection have to have references to the same RoleCoordinator instance. There's more than one way to implement that; you could make RoleCoordinator a public property of the row item, handle CollectionChanged on the ObservableCollection, and give each item a role coordinator as it's added to the collection. Here, I just passed it into the constructor because I'm initializing the collection statically in my window constructor for testing.

public class RoleCoordinator
{
    public event EventHandler<RoleChangedEventArgs> RoleChanged;

    public void RaiseRoleChanged(object sender, Role role)
    {
        RoleChanged?.Invoke(sender, new RoleChangedEventArgs(role));
    }
}

public class RoleChangedEventArgs : EventArgs
{
    public RoleChangedEventArgs(Role role)
    {
        Role = role;
    }

    public Role Role { get; set; }
}

Row item viewmodel

public class RowItemViewModel : ViewModelBase
{
    public RowItemViewModel(RoleCoordinator coordinator)
    {
        _roleCoordinator = coordinator;

        _roleCoordinator.RoleChanged += _roleCoordinator_RoleChanged;
    }

    #region Role Coordination
    private void _roleCoordinator_RoleChanged(object sender, RoleChangedEventArgs e)
    {
        if (sender != this && e.Role == Role.Primary && this.Role == Role.Primary)
        {
            Role = Role.Secondary;
        }
    }

    private RoleCoordinator _roleCoordinator;
    #endregion Role Coordination

    #region Role Property
    private Role _role = default(Role);
    public Role Role
    {
        get { return _role; }
        set
        {
            if (value != _role)
            {
                _role = value;

                _roleCoordinator.RaiseRoleChanged(this, this.Role);

                OnPropertyChanged();
            }
        }
    }
    #endregion Role Property