Question

I have 2 comboboxes. If i select a Activity in the 1st one, the related sub activities should be displayed in the second combobox.
The code looks fine as per MVVM style but when i select an activity on 1st one, the related subactivities in the 2nd combobox are not synched.
Here is my code:
View

<Window x:Class="TestDGCombosBinding.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TestDGCombosBinding"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <Grid.Resources>
        <ObjectDataProvider x:Key="ActivitiesDataProvider" ObjectType="{x:Type local:Activities}" MethodName="GetActivities"/>
        <local:DebugConverter x:Key="DebugConverter" />
    </Grid.Resources>
    <DataGrid 
        Grid.Row="1" Grid.Column="1" 
                 AutoGenerateColumns="False"                     
                 SelectionUnit="CellOrRowHeader"
                 SelectionMode="Single"
                 IsSynchronizedWithCurrentItem="True" 
                 RowBackground="White" 
                 AlternatingRowBackground="LightGray"                                          
                 AlternationCount="2" Name="dataGrid1" CurrentCellChanged="dataGrid1_CurrentCellChanged">
        <DataGrid.BindingGroup>
            <BindingGroup />
        </DataGrid.BindingGroup>
        <DataGrid.Resources>

        </DataGrid.Resources>

        <DataGrid.Columns>
            <DataGridTemplateColumn Header="Activities Custom" CanUserSort="True">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <ComboBox Text="{Binding CurrentActivity}"                                       
                                    SelectedValuePath="ActivityID"                                        
                                    DisplayMemberPath="ActivityName"
                                    ItemsSource="{Binding Source={StaticResource ActivitiesDataProvider}}"/>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
            <DataGridTemplateColumn Header="SubActivities Custom" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <ComboBox Text="{Binding CurrentSubActivity}"                                       
                                    SelectedValuePath="SubActivityID"                                      
                                    DisplayMemberPath="SubActivityname"
                                    ItemsSource="{Binding Path=SubActivitiesOfCurrentActivity}"/>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

        </DataGrid.Columns>
    </DataGrid>
</Grid>

---

Model

public class Activities
{
    public DataView GetActivities()
    {
        return ActivitiesAccess.GetAllActivities();
    }
}

---

ViewModel

public class ActivitiesViewModel : INotifyPropertyChanged
{
    public ActivitiesViewModel()
    { }
    private int currentActivity;

    public int CurrentActivity
    {
        get { return currentActivity; }
        set { 
                currentActivity = value;
                SubActivitiesOfCurrentActivity = ActivitiesAccess.GetAllSubActivitiesinActivity(currentActivity);
                OnPropertyChanged("CurrentActivity");
            }
    }

    private DataView subActivitiesOfCurrentActivity;

    public DataView SubActivitiesOfCurrentActivity
    {
        get {return subActivitiesOfCurrentActivity; }
        set
        {
            subActivitiesOfCurrentActivity = value;
            OnPropertyChanged("SubActivitiesOfCurrentActivity");
        }
    }

    private int currentSubActivity;

    public int CurrentSubActivity
    {
        get { return currentSubActivity; }
        set
        {
            currentSubActivity = value;
            OnPropertyChanged("CurrentSubActivity");
            }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

---

When i debug the code when i select an activity from the 1st drop down, the CurrentActivity property value is always 0 which im not sure why.
This value should be equal to the ActivityID of the selected activity.
I searched alot to get help but i couldnt find anything.
I will be very happy if someone could specify any problem in the code.

Answer 1

I resolved my issue.
When An Activity is Changed, the related Sub-Activities should be notified of the change.
But when the Sub-Activity is changed there is no need to notify the Activity.

I just commented OnPropertyChanged() call in CurrentSubActivity property.
Here is the code

private int currentSubActivity;

    public int CurrentSubActivity
    {
        get { return currentSubActivity; }
        set
        {
            //OnPropertyChanged("CurrentSubActivity");
            this.currentSubActivity = value;

        }
    }

I hope this helps someone out there too 🙂