Items collection must be empty before using ItemsSource

Question

I m trying to get images to display in a WPF ListView styled like a WrapPanel as described in this old ATC Avalon Team article  How to Create a Custom View     When I try to populate the ListView with a LINQ-to-Entities queried collection of ADO NET Entity Framework objects I get the following exception   Exception     Items collection must be empty before   using ItemsSource    My code hellip   Visual Basic  Private Sub Window1 Loaded      Handles MyBase Loaded     ListViewImages ItemsSource   From g In db Graphic                                    Order By g DateAdded Ascending                                    Select g End Sub   XAML   lt ListView Name  ListViewImages            SelectionMode  Single            ItemsSource   Binding   gt       lt local ImageView   gt   lt  ListView gt    I put a breakpoint on that line   ListViewImages ItemsSource is Nothing just before the LINQ assignment

User · Answer

In My case  it was just an extra StackPanel inside the ListView    lt ListView Name   details  Margin  50 0 50 0  gt               lt StackPanel Orientation  Vertical  gt                   lt StackPanel Orientation  Vertical  gt                       lt TextBlock Text   Binding Location LicenseName  StringFormat  Location   0      gt                       lt TextBlock Text   Binding Ticket Employee s name  StringFormat  Served by   0      gt                       lt TextBlock Text   Binding Ticket dt create time  StringFormat  Started at   0      gt                       lt Line StrokeThickness  2  Stroke  Gray  Stretch  Fill  Margin  0 5 0 5    gt                       lt ItemsControl ItemsSource   Binding Items    gt                   lt  StackPanel gt               lt  StackPanel gt           lt  ListView gt    Becomes    lt ListView Name   details  Margin  50 0 50 0  gt                   lt StackPanel Orientation  Vertical  gt                       lt TextBlock Text   Binding Location LicenseName  StringFormat  Location   0      gt                       lt TextBlock Text   Binding Ticket Employee s name  StringFormat  Served by   0      gt                       lt TextBlock Text   Binding Ticket dt create time  StringFormat  Started at   0      gt                       lt Line StrokeThickness  2  Stroke  Gray  Stretch  Fill  Margin  0 5 0 5    gt                       lt ItemsControl ItemsSource   Binding Items    gt                   lt  StackPanel gt           lt  ListView gt    and all is well

User · Answer

Keep template column inside DataGrid Columns  This helped me resolve this issue   Ref  DataGridTemplateColumn   Items collection must be empty before using ItemsSource

User · Answer

Perhaps not such an useful answer  but I had the same problem when changing column order and made mistake like the one in the following sample  Having a lot of columns  I reordered them and somehow pasted one after closing tag  DataGrid Columns           lt DataGridTemplateColumn x Name  addedDateColumn  Header  Added Date  Width  SizeToHeader  gt                   lt DataGridTemplateColumn CellTemplate gt                       lt DataTemplate gt                           lt TextBlock Text   Binding Path AddedDate     gt                       lt  DataTemplate gt                   lt  DataGridTemplateColumn CellTemplate gt               lt  DataGridTemplateColumn gt           lt  DataGrid Columns gt               lt DataGridTemplateColumn x Name  rowguidColumn  Header  rowguid  Width  SizeToHeader  gt                   lt DataGridTemplateColumn CellTemplate gt                       lt DataTemplate gt                           lt TextBlock Text   Binding Path rowguid     gt                       lt  DataTemplate gt                   lt  DataGridTemplateColumn CellTemplate gt               lt  DataGridTemplateColumn gt       lt  DataGrid gt    Anyway  lost half an hour because of this  Hope this helps others

User · Answer

Mine was with a datagrid Style  If you leave out the   lt DataGrid RowStyle gt  tags around the Style you get that problem  Weird thing is it worked for a while like that  Here is the bad code     lt DataGrid Name  DicsountScheduleItemsDataGrid                    Grid Column  0                    Grid Row  2                    AutoGenerateColumns  false                    ItemsSource   Binding DiscountScheduleItems  Mode OneWay   gt               lt Style TargetType  DataGridRow  gt                   lt Setter Property  IsSelected                          Value   Binding IsSelected  Mode TwoWay     gt               lt  Style gt    and the good    lt DataGrid Name  DicsountScheduleItemsDataGrid                    Grid Column  0                    Grid Row  2                    AutoGenerateColumns  false                    ItemsSource   Binding DiscountScheduleItems  Mode OneWay   gt               lt DataGrid RowStyle gt               lt Style TargetType  DataGridRow  gt                   lt Setter Property  IsSelected                          Value   Binding IsSelected  Mode TwoWay     gt               lt  Style gt               lt  DataGrid RowStyle gt

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I had this same error for a while in a slightly different scenario  I had    lt wpftoolkit DataGrid     AutoGenerateColumns  False      ItemsSource   Binding Path Accounts    gt       lt wpftoolkit DataGridTextColumn          Header  Account Name           Binding   Binding Path AccountName     gt   lt  wpftoolkit DataGrid gt    which I fixed to be   lt wpftoolkit DataGrid     AutoGenerateColumns  False      ItemsSource   Binding Path Accounts    gt       lt wpftoolkit DataGrid Columns gt           lt wpftoolkit DataGridTextColumn              Header  Account Name               Binding   Binding Path AccountName     gt       lt  wpftoolkit DataGrid Columns gt   lt  wpftoolkit DataGrid gt

User · Answer

I had the same error  The problem was this extra symbol     added by mistake between the tags  lt  ComboBox SelectedValue gt  and  lt  ComboBox gt     lt ComboBox     ItemsSource   Binding StatusTypes      DisplayMemberPath  StatusName     SelectedValuePath  StatusID  gt      lt ComboBox SelectedValue gt         lt Binding Path  StatusID   gt      lt  ComboBox SelectedValue gt      gt   lt  ComboBox gt    and here is the correct code    lt ComboBox     ItemsSource   Binding StatusTypes      DisplayMemberPath  StatusName     SelectedValuePath  StatusID  gt      lt ComboBox SelectedValue gt         lt Binding Path  StatusID   gt      lt  ComboBox SelectedValue gt   lt  ComboBox gt

User · Answer

Beware of typos  I had the following    lt TreeView ItemsSource   Binding MyCollection   gt       lt TreeView Resources gt                   lt  TreeView Resouces gt  gt   lt  TreeView gt     Notice the tailing    which is interpreted as content  so you re setting twice the content    Took me a while

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Me too on a different scenario    lt ComboBox Cursor  Hand  DataContext   Binding                   FontSize  16  Height  27  ItemsSource   Binding                  Name  cbxDamnCombo  SelectedIndex  0  SelectedValuePath  MemberId  gt            lt DataTemplate gt               lt TextBlock DataContext   Binding   gt                   lt TextBlock Text gt                     lt MultiBinding StringFormat     0     1   gt                       lt Binding Path  MemberName   gt                       lt Binding Path  Phone   gt                     lt  MultiBinding gt                   lt  TextBlock Text gt               lt  TextBlock gt           lt  DataTemplate gt    lt  ComboBox gt    Now when you complete with the missing tag Control ItemTemplate  everything gets to normal    lt ComboBox Cursor  Hand  DataContext   Binding                   FontSize  16  Height  27  ItemsSource   Binding                  Name  cbxDamnCombo  SelectedIndex  0  SelectedValuePath  MemberId  gt       lt ComboBox ItemTemplate gt           lt DataTemplate gt               lt TextBlock DataContext   Binding   gt                   lt TextBlock Text gt                     lt MultiBinding StringFormat     0     1   gt                       lt Binding Path  MemberName   gt                       lt Binding Path  Phone   gt                     lt  MultiBinding gt                   lt  TextBlock Text gt               lt  TextBlock gt           lt  DataTemplate gt       lt ComboBox ItemTemplate gt   lt  ComboBox gt

User · Answer

In my case  it was not using a DataTemplate for the ItemsControl   Old    lt ItemsControl Width  243  ItemsSource   Binding List  Mode TwoWay   gt       lt StackPanel Orientation  Horizontal  gt           lt TextBox Width  25  Margin  0 0 5 0  Text   Binding Path Property1    gt           lt Label Content   Binding Path Property2    gt       lt  StackPanel gt   lt  ItemsControl gt    New    lt ItemsControl Width  243  ItemsSource   Binding List  Mode TwoWay   gt       lt ItemsControl ItemTemplate gt           lt DataTemplate gt               lt StackPanel Orientation  Horizontal  gt                   lt TextBox Width  25  Margin  0 0 5 0  Text   Binding Path Property1    gt                   lt Label Content   Binding Path Property2    gt               lt  StackPanel gt           lt  DataTemplate gt       lt  ItemsControl ItemTemplate gt   lt  ItemsControl gt

User · Answer

The reason this particular exception gets thrown is that the content of the  element gets applied to the ListView s Items collection   So the XAML initialises the ListView with a single local ImageView in its Items collection   But when using an ItemsControl you must use either the Items property or the ItemsSource property  you can t use both at the same time   Hence when the ItemsSource attribute gets processed an exception is thrown   You can find out which property the content of an element will get applied to by looking for the ContentPropertyAttribute on the class   In this case it s defined higher in the class hierarchy  on the ItemsControl    ContentPropertyAttribute  Items      The intention here was that the ListView s View be set to a local ImageView so the fix is to explicitly indicate the property to be set   Fix the XAML and the exception goes away    lt ListView Name  ListViewImages            SelectionMode  Single            ItemsSource   Binding   gt       lt ListView View gt           lt local ImageView   gt       lt  ListView View gt   lt  ListView gt    It was missing that  lt ListView View gt  tag

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I encountered this error in another situation  I tried to defined a style for TreeViewItems directly within the  lt TreeView gt   but instead should have embedded that within  lt TreeView ItemContainerStyle gt    Wrong    lt TreeView ItemsSource   Binding ExampleListView   gt       lt Style TargetType   x Type TreeViewItem   gt           lt Setter Property  IsExpanded  Value   Binding IsExpanded  Mode TwoWay    gt           lt Setter Property  IsSelected  Value   Binding IsSelected  Mode TwoWay    gt       lt  Style gt       lt TreeView ItemTemplate gt           lt HierarchicalDataTemplate ItemsSource   Binding SubItemListList   gt                       lt  HierarchicalDataTemplate gt       lt  TreeView ItemTemplate gt   lt  TreeView gt    Correct    lt TreeView ItemsSource   Binding ExampleListView   gt       lt TreeView ItemContainerStyle gt           lt Style TargetType  TreeViewItem  gt               lt Setter Property  IsExpanded  Value   Binding IsExpanded  Mode TwoWay    gt               lt Setter Property  IsSelected  Value   Binding IsSelected  Mode TwoWay    gt           lt  Style gt       lt  TreeView ItemContainerStyle gt       lt TreeView ItemTemplate gt           lt HierarchicalDataTemplate ItemsSource   Binding SubItemListList   gt                       lt  HierarchicalDataTemplate gt       lt  TreeView ItemTemplate gt   lt  TreeView gt

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To state the answer differently      In Xaml verify that there are no Missing Parent Nodes or incorrect nodes in the defined areas    For example  This Is Failing   There is no proper parent for the ItemsPanelTemplate child node below    lt ItemsControl ItemsSource   Binding TimeSpanChoices   gt       lt ItemsPanelTemplate gt           lt UniformGrid Rows  1    gt       lt  ItemsPanelTemplate gt           lt  ItemsControl gt    This Is Working    lt ItemsControl ItemsSource   Binding TimeSpanChoices   gt       lt ItemsControl ItemsPanel gt   lt  -- I am the missing parent  -- gt           lt ItemsPanelTemplate gt               lt UniformGrid Rows  1    gt           lt  ItemsPanelTemplate gt       lt  ItemsControl ItemsPanel gt               lt  ItemsControl gt     There is a proper parent node of  lt ItemsControl ItemsPanel gt  provided

User · Answer

Exception      Items collection must be empty before using ItemsSource    This exception occurs when you add items to the ItemsSource through different sources  So Make sure you haven t accidentally missed a tag  misplaced a tag  added extra tags  or miswrote a tag    lt  --Right-- gt    lt ItemsControl ItemsSource   Binding MyItems   gt        lt ItemsControl ItemsPanel     gt        lt ItemsControl MyAttachedProperty     gt        lt FrameworkElement ActualWidth     gt   lt  ItemsControl gt     lt  --WRONG-- gt    lt ItemsControl ItemsSource   Binding MyItems   gt        lt Grid     gt        lt Button     gt        lt DataTemplate     gt        lt Heigth     gt   lt  ItemsControl gt      While ItemsControl ItemsSource is already set through Binding  other items  Grid  Button       can t be added to the source  However while ItemsSource is not in-use the following code is allowed    lt  --Right-- gt   lt ItemsControl gt        lt Button     gt        lt TextBlock     gt        lt sys String     gt   lt  ItemsControl gt    notice the missing ItemsSource   Binding MyItems   part

User · Answer

I had this same error in a different scenario   lt ItemsControl ItemsSource   Binding TableList   gt       lt ItemsPanelTemplate gt           lt WrapPanel Orientation  Horizontal   gt       lt  ItemsPanelTemplate gt   lt  ItemsControl gt    The solution was to add the ItemsControl ItemsPanel tag before the ItemsPanelTemplate   lt ItemsControl ItemsSource   Binding TableList   gt       lt ItemsControl ItemsPanel gt           lt ItemsPanelTemplate gt               lt WrapPanel Orientation  Horizontal   gt           lt  ItemsPanelTemplate gt       lt  ItemsControl ItemsPanel gt   lt  ItemsControl gt

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I ve had this error when I tried applying context menus to my TreeView  Those tries ended up in a bad XAML which compiled somehow      lt TreeView Height  Auto  MinHeight  100   ItemsSource   Binding Path TreeNodes  Mode TwoWay        ContextMenu   Binding Converter  StaticResource ContextMenuConverter    gt      ContextMenu    gt       lt TreeView ItemContainerStyle gt              Note the problematic line  ContextMenu    gt    I don t know why it compiled  but I figured it s worth mentioning as a reason for this cryptic exception message  Like Armentage said  look around the XAML carefully  especially in places you ve recently edited

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I just ran into a VERY insidious example of this problem   My original fragment was much more complex  which made it difficult to see the error       lt ItemsControl                  Foreground  Black   Background  White  Grid IsSharedSizingScope  True        x Name  MyGrid  ItemsSource   Binding   gt         gt         lt ItemsControl ItemsPanel gt              lt  -- All is fine here -- gt         lt  ItemsControl ItemsPanel gt         lt ItemsControl ItemTemplate gt              lt  -- All is fine here -- gt         lt  ItemsControl ItemTemplate gt         lt  -- Have you caught the error yet  -- gt       lt  ItemsControl gt    The bug    The extra   after the initial opening  lt ItemsControl gt  tag   The  lt  got applied to the built-in Items collection   When the DataContext was later set  instant crashola   So look out for more than just errors surround your ItemsControl specific data children when debugging this problem

User · Answer

I ran into this problem because one level of tag   lt ListView View gt  to be specirfic  was missing in my XAML   This code produced this error    lt Grid gt       lt ListView Margin  10  Name  lvDataBinding   gt           lt GridView gt               lt GridViewColumn Header  Name  Width  120  DisplayMemberBinding   Binding Name     gt               lt GridViewColumn Header  Age  Width  50  DisplayMemberBinding   Binding Age     gt               lt GridViewColumn Header  Mail  Width  150  DisplayMemberBinding   Binding Mail     gt           lt  GridView gt       lt  ListView gt   lt  Grid gt    The following fixed it   lt Grid gt       lt ListView Margin  10  Name  lvDataBinding   gt           lt ListView View gt   lt  -- This was missing in top  -- gt               lt GridView gt                   lt GridViewColumn Header  Name  Width  120  DisplayMemberBinding   Binding Name     gt                   lt GridViewColumn Header  Age  Width  50  DisplayMemberBinding   Binding Age     gt                   lt GridViewColumn Header  Mail  Width  150  DisplayMemberBinding   Binding Mail     gt               lt  GridView gt           lt  ListView View gt       lt  ListView gt   lt  Grid gt

[.net] "Items collection must be empty before using ItemsSource."

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