WPF DataGrid - add new row / DataContext

Question

I have multiple DataGrids to manage the data of my database. The functionallity also includes adding new rows. The problem is though, that in my given example there is a dependency between the created row, and the DataGrid's DataContext set by another DataGrid. In my case I've got:

Parties - A party can have n Tracks. If you change the selection of the Party DataGrid, you change the view of the Track DataGrid.

Tracks - A Track has essentially a reference back to the Party.

XAML:

        <DataGrid AutoGenerateColumns="False" SelectionMode="Single" DataContext="{Binding CurrentParty}" ItemsSource="{Binding Tracks}" SelectedItem="{Binding CurrentTrack}">
            <DataGrid.ContextMenu>
                <ContextMenu>
                    <MenuItem Header="_Delete" Command="{Binding DeleteTrackCommand}"/>
                </ContextMenu>
            </DataGrid.ContextMenu>
            <DataGrid.Columns>
                <DataGridTextColumn IsReadOnly="True" Header="Votes" Binding="{Binding Path=Votes}">
                    <DataGridTextColumn.CellStyle>
                        <Style TargetType="DataGridCell">
                            <Setter Property="Background" Value="LightGray" />
                        </Style>
                    </DataGridTextColumn.CellStyle>
                </DataGridTextColumn>
                <DataGridTemplateColumn Header="Interpret" IsReadOnly="False">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=Interpret}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                    <DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <TextBox Text="{Binding Path=Interpret}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellEditingTemplate>
                </DataGridTemplateColumn>
                <DataGridTemplateColumn Header="Title" IsReadOnly="False">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=Title}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                    <DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <TextBox Text="{Binding Path=Title}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellEditingTemplate>
                </DataGridTemplateColumn>
                <DataGridTemplateColumn Header="URL" IsReadOnly="False">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=Url}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                    <DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <TextBox Text="{Binding Path=Url}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellEditingTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>

Code in ViewModel:

public TrackVM() {
   // requires the "CurrentParty" from DataContext.
}

I could access the DataContext in the code behind, but that would kinda break the MVVM architecture, wouldn't it. What I want to do / have instead is: pass the CurrentParty object to the default constructor.

Johannes Johannes · Accepted Answer · 2014-12-13T19:43:25

As a workaround I did the following: I wrapped the TrackVM in a ObservableCollection in a wrapper class called TracksVM. There I registered a function to the CollectionChanged event of the collection. This eventhandler sets the needed reference via a property if a new TrackVM has been added.

WPF DataGrid - add new row / DataContext

1 Answers