如何从DataGrid WPF中的ComboBox列获取SelectedItem属性

Question

recently we started to use WPF at work. Now I want to create a DataGrid from a list of objects (DataGrid ItemSource) that contains a project role, the employee that should do the job and a list of employees that could also do that job. Lets call this list the "MainList". In that DataGrid is a ComboBox Column that uses another list of objects as ItemSource where you can change the employee for the job. I will call this list the "ChildList". This list is included in the MainList (as allready mentioned) and I bind it by using the correct BindingPath. So far so good. Now I have to set the SelectedItem (to show which Employee is currently selected). From the MainList I can get the employee that should be selected from the ChildList. Obviously I cant do this by Binding. Unfortunatly I cant get the SelectedItem property in the code-behind. Basically I need to go through every row from the DataGrid and get the Item that should be selected in the ComboBox. Then I would go through the ComboBox Items until I find the matching Item and set this as SelectedItem. But I cant find a way to do this.

I tried using a DataGridComboBoxColumn aswell but it has only the SelectedItemBinding property and since you cant compare while binding this should not work. I also tried to get every cell in the code-behind, that is a ComboBox but without success so far.

<DataGrid x:Name="DgvProjectTeam" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" AutoGenerateColumns="False" Margin="0" RowHeight="40" CanUserAddRows="False" BorderThickness="1" VerticalScrollBarVisibility="Auto" HorizontalGridLinesBrush="#FFA2B5CD" VerticalGridLinesBrush="#FFA2B5CD" ItemsSource="{Binding}" VirtualizingStackPanel.IsVirtualizing="False">
  <DataGrid.Columns>
      <DataGridTemplateColumn Header="Resource" Width="200" x:Name="DgtProjectCoreTeam">
           <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                      <ComboBox Name="CbxResource" ItemsSource="{Binding Path=ListOfPossibleResources}" DisplayMemberPath="ResourceOfQMatrix.Fullname"/>
                 </DataTemplate>
           </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>

The DataGrid shows everything I need. I just dont know how I can set the SelectedItem for each of the generated ComboBoxCells in the code-behind.

Anyone an idea?

Answer 1

Here's a quick example of what you can do. First, define your view models that will be bound to the DataGrid . Ideally, these view models would raise PropertyChanged or CollectionChanged when their properties are changed, but for this simple example this is not needed.

public class ViewModel
{
    public List<ProjectRoleViewModel> ProjectRoles { get; set; }
}

public class ProjectRoleViewModel
{
    public string Role { get; set; }
    public string Employee { get; set; }
    public List<string> OtherEmployees { get; set; }
    public string SelectedOtherEmployee { get; set; }
}

I've hard-coded some dummy values to have data in the view models:

var viewModel = new ViewModel
{
    ProjectRoles = new List<ProjectRoleViewModel>
    {
        new ProjectRoleViewModel
        {
            Role = "Designer",
            Employee = "John Smith",
            OtherEmployees = new List<string> {"Monica Thompson", "Robert Gavin"}
        },
        new ProjectRoleViewModel
        {
            Role = "Developer",
            Employee = "Tom Barr",
            OtherEmployees = new List<string> {"Jason Ross", "James Moore"}
        }
    }
};

This view model then needs to be assigned to the DataContext of your Window or UserControl that contains the DataGrid . Here's the XAML for the DataGrid :

<DataGrid
    ItemsSource="{Binding ProjectRoles}"
    AutoGenerateColumns="False"
    >
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding Role}" />
        <DataGridTextColumn Binding="{Binding Employee}" />
        <DataGridTemplateColumn>
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <ComboBox
                        ItemsSource="{Binding OtherEmployees}"
                        SelectedItem="{Binding SelectedOtherEmployee, UpdateSourceTrigger=PropertyChanged}"
                        />
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

After the user picks the "other" employee that can do the job, the view model's SelectedOtherEmployee will have the chosen value. You don't need any code-behind in this case, everything's contained in the view models.