How to add a XAML Resource (Grid with ItemsControls) to a FlowDocument in Code-Behind multiple times

Question

I am working on a WPF Window that presents the results of some technical calculations inside a FlowDocumentViewer.

Problem: The FlowDocument and all its content is created from Code-Behind because every calculation differs a bit in terms of headers, shown results, and lines. I use different BlockUIContainers which hold a Resource Grid with some ItemsControls to show the results in a formatted order and add it to a Section and then to the Blocks of the Document, but only the last Block is shown inside the Reader. I don't understand why after using FlowDoc.Blocks.Add(section) multiple times, only the last Block is shown.

I have created a Resource inside the XAML Code to fill it from Code Behind with the results. I need the output to look like this, eg:

---

      M,ed                                =       70 kNm
      Q,ed                                =       25 kN
      N,ed                                =       30 kN
      ...
   

To achieve formatting like this, I created a grid with three columns, each containing an ItemsControl with a DataTemplate TextBlock, which has a Binding to a List<> of results.

 <Window x:Class="FaceplateInput.Output" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:local="clr-namespace:FaceplateInput" mc:Ignorable="d" x:Name="OutputWnd" WindowStartupLocation="CenterScreen" Title="Output" Height="1000" Width="700"> <Window.Resources> <Grid x:Key ="TestGrid" x:Name="Grid"> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> <ColumnDefinition Width="*"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="*"/> </Grid.RowDefinitions> <ItemsControl x:Name="ItemsLeft" Grid.Column="0"> <ItemsControl.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding}"/> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> <ItemsControl x:Name="ItemsMid" Grid.Column="1"> <ItemsControl.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding}"/> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> <ItemsControl x:Name="ItemsRight" Grid.Column="2"> <ItemsControl.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding}"/> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </Grid> </Window.Resources>... <FlowDocumentScrollViewer x:Name="DocReader" Grid.Column="1" Grid.Row="2" Margin="20" MaxWidth="700"> </FlowDocumentScrollViewer> </Grid> </Window>

I want to create the FlowDocument in Code-Behind to have control over formatting, especially because the document is created from a single string that is returned by the calculating class.
I build the following test-method to see how FlowDocuments work. The result is that only the added paragraphs and the last section are shown in the output window. Code-Behind:

namespace FaceplateInput
{
    public partial class Output: Window
    {
        public string PathToImage;
        public string PathToBackground;
        public string PathToTXTFile;
        public Output()
        {
            InitializeComponent();
            CreateFlowDocument();
        }

        private void CreateFlowDocument()
        {
            FlowDocument FlowDoc = new FlowDocument();
            
            List<string> leftStr = new List<string>();
            List<string> midStr = new List<string>();
            List<string> rightStr = new List<string>();
            //for Testing purposes, i create some weired data to fill the Lists
            for (int i = 0; i < 10; i++)
            {
                leftStr.Add($"LeftLine {i + 1}");
                midStr.Add("=");
                rightStr.Add($"RightLine {i + 1}");
            }

            //Creating a new Container with Resource Grid as UIElement:
            BlockUIContainer cont = new BlockUIContainer((UIElement)this.FindResource("TestGrid"));
            Grid child = (Grid)cont.Child;
            //setting the sources for the ItemsControl:
            ItemsControl items1 = (ItemsControl)child.Children[0];
            items1.ItemsSource = leftStr;
            ItemsControl items2 = (ItemsControl)child.Children[1];
            items2.ItemsSource = midStr;
            ItemsControl items3 = (ItemsControl)child.Children[2];
            items3.ItemsSource = rightStr;
            
            //adding section holding BlockUIContainer to Document  
            Section section = new Section();
            section.Blocks.Add(cont);
            FlowDoc.Blocks.Add(section);
        
            //disconnecting UIContainer from parent to avoid Exception
            section.RemoveChild(cont.Child);
            cont.Child = null;
            
            //another "testline" to see where it puts it in the document
            FlowDoc.Blocks.Add(new Paragraph(new Run("TestString 1\n")));
            
            //all the stuff above again to test
            leftStr.Clear();
            midStr.Clear();
            rightStr.Clear();
            leftStr.Add("______");
            midStr.Add("_____________________");
            rightStr.Add("_____________________");
            for (int i = 0; i < 20; i++)
            {
                leftStr.Add($"Left: {(double)i * 324 / 10}\n");
                midStr.Add("=\n");
                rightStr.Add($"{(double)i * 13 / 2}\n");
            }

            BlockUIContainer cont1 = new BlockUIContainer((UIElement)this.FindResource("TestGrid"));
            Grid child1 = (Grid)cont1.Child;
            items1 = (ItemsControl)child1.Children[0];
            items1.ItemsSource = leftStr;
            items2 = (ItemsControl)child1.Children[1];
            items2.ItemsSource = midStr;
            items3 = (ItemsControl)child1.Children[2];
            items3.ItemsSource = rightStr;

            Section section1 = new Section();
            section1.Blocks.Add(cont1);
            FlowDoc.Blocks.Add(new Paragraph(new Run("TestString 2\n")));
            FlowDoc.Blocks.Add(section1);

            FlowDoc.Blocks.Add(new Paragraph(new Run("TestString 3\n")));
            
            DocReader.Document = FlowDoc;
        }
        //...
    }
}

I'd appreciate any tips on how to get this working, and maybe how to improve the code itself, or any ideas for completely different approaches. Greets and thx, Crawliiee

Answer 1

You are setting the first container to null, so that first section is empty. Remove this line:

cont.Child = null;

An alternative could be to use a ListView with GroupView as in the example

https://docs.microsoft.com/en-us/dotnet/api/system.windows.controls.listview?view=netframework-4.7.2&f1url=%3FappId%3DDev16IDEF1%26l%3DEN-US%26k%3Dk(System.Windows.Controls.ListView);k(TargetFrameworkMoniker-.NETFramework,Version%253Dv4.7.2);k(DevLang-csharp)%26rd%3Dtrue