Question

This may sound trivial but i have a problem with setting selected item in ComboBox 😉

What i want to achive:

I want to have the first element of the list selected after the page loads.

XAML Code:

               <DataTemplate>
                                    <ComboBox x:Name="DeviceComboBox" SelectedIndex="1" SelectionChanged="DeviceComboBox_SelectionChanged">
                                        <ComboBox.Items>
                                            <ComboBoxItem x:Name="Switch" Content="Switche"/>
                                            <ComboBoxItem x:Name="Firewall" Content="Firewalle"/>
                                            <ComboBoxItem x:Name="Host" Content="Hosty" />
                                            <ComboBoxItem x:Name="SRF1" Content="SRF1"/>
                                        </ComboBox.Items>
                                    </ComboBox>
                                </DataTemplate>

RESULT:
AG_E_UKNOWN_ERROR [Line:49 Position:55]
Line 49:

</ComboBox>

Error Details

    w MS.Internal.XcpImports.MethodEx(IntPtr ptr, String name, CValue[] cvData)
    w MS.Internal.XcpImports.MethodEx(DependencyObject obj, String name)
    w MS.Internal.XcpImports.DataTemplate_LoadContent(DataTemplate template)
    w System.Windows.Controls.DataGridTemplateColumn.GenerateElement(DataGridCell cell, Object dataItem)
    w System.Windows.Controls.DataGrid.PopulateCellContent(Boolean isCellEdited, DataGridColumn dataGridColumn, DataGridRow dataGridRow, DataGridCell dataGridCell)
    w System.Windows.Controls.DataGrid.AddNewCellPrivate(DataGridRow row, DataGridColumn column)
    w System.Windows.Controls.DataGrid.CompleteCellsCollection(DataGridRow dataGridRow)
    w System.Windows.Controls.DataGrid.GenerateRow(Int32 rowIndex, Int32 slot, Object dataContext)
    w System.Windows.Controls.DataGrid.InsertElementAt(Int32 slot, Int32 rowIndex, Object item, DataGridRowGroupInfo groupInfo, Boolean isCollapsed)
    w System.Windows.Controls.DataGrid.InsertRowAt(Int32 rowIndex)
    w System.Windows.Controls.DataGridDataConnection.NotifyingDataSource_CollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
    w System.Windows.Data.PagedCollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
    w System.Windows.Data.PagedCollectionView.ProcessAddEvent(Object addedItem, Int32 addIndex)
    w System.Windows.Data.PagedCollectionView.ProcessCollectionChanged(NotifyCollectionChangedEventArgs args) 
    w System.Windows.Data.PagedCollectionView.<.ctor>b__0(Object sender, NotifyCollectionChangedEventArgs args)
    w System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    w System.Collections.ObjectModel.ObservableCollection`1.InsertItem(Int32 index, T item)
    w System.Collections.ObjectModel.Collection`1.Add(T item)
    w LANOS.Views.Customers.onCustomerListLoaded(LoadOperation`1 loadOper)
    w System.ServiceModel.DomainServices.Client.DomainContext.<>c__DisplayClass13`1.<Load>b__11(LoadOperation lo)
    w System.ServiceModel.DomainServices.Client.LoadOperation.<>c__DisplayClass4`1.<Create>b__0(LoadOperation`1 arg)
    w System.ServiceModel.DomainServices.Client.LoadOperation`1.InvokeCompleteAction()
    w System.ServiceModel.DomainServices.Client.OperationBase.Complete(Object result)
    w System.ServiceModel.DomainServices.Client.LoadOperation.Complete(DomainClientResult result)
    w System.ServiceModel.DomainServices.Client.DomainContext.CompleteLoad(IAsyncResult asyncResult)
    w System.ServiceModel.DomainServices.Client.DomainContext.<>c__DisplayClass1b.<Load>b__17(Object )

Caused by: AG_E_UNKNOWN_ERROR [Line: 49 Position: 55]

    w MS.Internal.XcpImports.MethodEx(IntPtr ptr, String name, CValue[] cvData)
    w MS.Internal.XcpImports.MethodEx(DependencyObject obj, String name)
    w MS.Internal.XcpImports.DataTemplate_LoadContent(DataTemplate template)
    w System.Windows.Controls.DataGridTemplateColumn.GenerateElement(DataGridCell cell, Object dataItem)
    w System.Windows.Controls.DataGrid.PopulateCellContent(Boolean isCellEdited, DataGridColumn dataGridColumn, DataGridRow dataGridRow, DataGridCell dataGridCell)
    w System.Windows.Controls.DataGrid.AddNewCellPrivate(DataGridRow row, DataGridColumn column)
    w System.Windows.Controls.DataGrid.CompleteCellsCollection(DataGridRow dataGridRow)
    w System.Windows.Controls.DataGrid.GenerateRow(Int32 rowIndex, Int32 slot, Object dataContext)
    w System.Windows.Controls.DataGrid.InsertElementAt(Int32 slot, Int32 rowIndex, Object item, DataGridRowGroupInfo groupInfo, Boolean isCollapsed)
    w System.Windows.Controls.DataGrid.InsertRowAt(Int32 rowIndex)
    w System.Windows.Controls.DataGridDataConnection.NotifyingDataSource_CollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
    w System.Windows.Data.PagedCollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
    w System.Windows.Data.PagedCollectionView.ProcessAddEvent(Object addedItem, Int32 addIndex)
    w System.Windows.Data.PagedCollectionView.ProcessCollectionChanged(NotifyCollectionChangedEventArgs args)
    w System.Windows.Data.PagedCollectionView.<.ctor>b__0(Object sender, NotifyCollectionChangedEventArgs args)
    w System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    w System.Collections.ObjectModel.ObservableCollection`1.InsertItem(Int32 index, T item)
    w System.Collections.ObjectModel.Collection`1.Add(T item)
    w LANOS.Views.Customers.onCustomerListLoaded(LoadOperation`1 loadOper)
    w System.ServiceModel.DomainServices.Client.DomainContext.<>c__DisplayClass13`1.<Load>b__11(LoadOperation lo)
    w System.ServiceModel.DomainServices.Client.LoadOperation.<>c__DisplayClass4`1.<Create>b__0(LoadOperation`1 arg)
    w System.ServiceModel.DomainServices.Client.LoadOperation`1.InvokeCompleteAction()
    w System.ServiceModel.DomainServices.Client.OperationBase.Complete(Object result)
    w System.ServiceModel.DomainServices.Client.LoadOperation.Complete(DomainClientResult result)
    w System.ServiceModel.DomainServices.Client.DomainContext.CompleteLoad(IAsyncResult asyncResult)
    w System.ServiceModel.DomainServices.Client.DomainContext.<>c__DisplayClass1b.<Load>b__17(Object )

Any ideas?

Answer 1

As I read in your comments you want to use a ComboBox which automatically has a selection when it is loaded. Therefore I would suggest two possibilities: Writing a control deriving from ComboBox or adding a behavior to a default ComboBox.

Deriving from ComboBox:

public class MyComboBox : ComboBox
{
  public MyComboBox()
  {
    Loaded += ComboBoxLoaded;
  }

  private void ComboBoxLoaded(object sender, RoutedEventArgs e)
  {
    if(Count > 1)
    {
      SelectedIndex = 1;
    }
  }
}

Usage:

<MyComboBox>
  <ComboBoxItem x:Name="Switch" Content="Switche"/>
  <ComboBoxItem x:Name="Firewall" Content="Firewalle"/>
  <ComboBoxItem x:Name="Host" Content="Hosty" />
  <ComboBoxItem x:Name="SRF1" Content="SRF1"/>
</MyComboBox>

Implementing behavior:

A behavior class allows you to add a behavior to a control using xaml. The behavior is coded.

public class ComboBoxSelectionBehavior:Behavior<ComboBox>
{
  protected override void OnAttached()
  {
    base.OnAttached();
    AssociatedObject.Loaded += ComboBoxLoaded;
  }

  protected override void OnDetaching()
  {
    AssociatedObject.Loaded -= ComboBoxLoaded;
    base.OnDetaching();
  }

  private void ComboBoxLoaded(object sender, RoutedEventArgs e)
  {
    if(Count > 1)
    {
      SelectedIndex = 1;
    }
  }
}

Usage:

<ComboBox>
  <Interactivity:Interaction.Behaviors>
    <Behaviors:ComboBoxSelectionBehavior/>
  </Interactivity:Interaction.Behaviors>
  <ComboBoxItem x:Name="Switch" Content="Switche"/>
  <ComboBoxItem x:Name="Firewall" Content="Firewalle"/>
  <ComboBoxItem x:Name="Host" Content="Hosty" />
  <ComboBoxItem x:Name="SRF1" Content="SRF1"/>
</ComboBox>

Note, that for the usage of behaviors you need the Blend SDK to be installed.