trying to download the word document using open xml from dot net core mvc getting an error

Question

I am trying to generate the word document using open XML plugin in Dot net core by writing code in action result method inside controller like this below

    public IActionResult CreateDocument()
    {
        using (MemoryStream mem = new MemoryStream())
        {
            using (WordprocessingDocument wordDoc = WordprocessingDocument.Create(mem, WordprocessingDocumentType.Document, true))
            {
                wordDoc.AddMainDocumentPart();
                Document doc = new Document();

                //Body body = new Body();

                /// Add header
                MainDocumentPart mainDocPart = wordDoc.MainDocumentPart;

                HeaderPart headerPart1 = mainDocPart.AddNewPart<HeaderPart>("r97");

                Header header1 = new Header();

                Paragraph paragraph1 = new Paragraph() { };
                Run run1 = new Run();
                Text text1 = new Text();
                text1.Text = "This is Header Part";

                run1.Append(text1);
                paragraph1.Append(run1);
                header1.Append(paragraph1);

                headerPart1.Header = header1;

                // getting an error here in this line
                SectionProperties sectionProperties1 = mainDocPart.Document.Body.Descendants<SectionProperties>().FirstOrDefault();  
                if (sectionProperties1 == null)
                {
                    sectionProperties1 = new SectionProperties() { };
                    mainDocPart.Document.Body.Append(sectionProperties1);
                }
                HeaderReference headerReference1 = new HeaderReference() { Type = HeaderFooterValues.Default, Id = "r97" };
                sectionProperties1.InsertAt(headerReference1, 0);
             .......
            ........
            .........
           }
        }
     }

but some how getting an error at this line SectionProperties sectionProperties1 = mainDocPart.Document.Body.Descendants<SectionProperties>().FirstOrDefault();

**Error:** DocumentFormat.OpenXml.Packaging.MainDocumentPart.Document.get returned null.

i am not sure where i am doing wrong with this code, Could any one please suggest any idea on this one

many thanks in advance

Answer 1

You instantiate the mainDocPart variable at this line:
MainDocumentPart mainDocPart = wordDoc.MainDocumentPart;

Then you did not add any document in it. That's why you are got the error: DocumentFormat.OpenXml.Packaging.MainDocumentPart.Document.get returned null.

How to solve it:

mainDocPart.Document = doc; //you define earlier but do not used.
doc.Body = new Body();
SectionProperties sectionProperties1 = 
mainDocPart.Document.Body.Descendants<SectionProperties>()?.FirstOrDefault();  
if (sectionProperties1 == null)
{
    sectionProperties1 = new SectionProperties() { };
    mainDocPart.Document.Body.Append(sectionProperties1);
}

You can get more information about it in this doc page: https://learn.microsoft.com/en-us/dotnet/api/documentformat.openxml.wordprocessing.document?redirectedfrom=MSDN&view=openxml-2.8.1