Aspose.Words adding paragraphs via DocumentBuilder does not update Document info

Question

I'm trying to write a extension method for Aspose's DocumentBuilder class that allows you to check if inserting a number of paragraphs into a document will cause a page break or not, I hoped this would be rather simple, but it turns out otherwise:

public static bool WillPageBreakAfter(this DocumentBuilder builder, int numParagraphs) 
{
    // Get current number of pages
    int pageCountBefore = builder.Document.PageCount;

    for (int i = 0; i < numParagraphs; i++) 
    {
        builder.InsertParagraph();
    }

    // Get the number of pages after adding those paragraphs
    int pageCountAfter = builder.Document.PageCount;

    // Delete the paragraphs, we don't need them anymore
    ...

    if (pageCountBefore != pageCountAfter) 
    {
        return true;
    } 
    else  
    {
        return false;
    }
} 

MY problem is, that inserting paragraphs does not seem to update the builder.Document.PageCount property. Even plugging in something crazy like 5000 paragraphs does seem to modify that property. I've also tried InsertBreak() (including using BreakType.PageBreak) and Writeln() but those don't work either.

What's going on here? Is there anyway I can achieve the desired result?

UPDATE

It seems that absolutely nothing done on the DocumentBuilder parameter actually happens on the DocumentBuilder that is calling the method. In other words:

If I modify the for loop to do something like builder.InsertParagraph(i.ToString()); and then remove the code that deletes the paragraphs afterwords. I can call:

myBuilder.WillPageBreakAfter(10);

And expect to see 0-9 written to the document when it is saved, however it is not. None of the Writeln()s in the extension methods seem to do anything at all.

UPDATE 2

It appears for what ever reasons, I cannot write anything with the DocumentBuilder after accessing the page count. So calling something like Writeln() before the int pageCountBefore = builder.Document.PageCount; line works, but trying to write after that line simply does nothing.

Answer 1

And it seems I've figured it out.

From the Aspose docs:

// This invokes page layout which builds the document in memory so note that with large documents this 
// property can take time. After invoking this property, any rendering operation e.g rendering to PDF or image 
// will be instantaneous. 
int pageCount = doc.PageCount;

The most important line here:

This invokes page layout

By "invokes page layout", they mean it calls UpdatePageLayout(), for which the docs contain this note:

However, if you modify the document after rendering and then attempt to render it again - Aspose.Words will not update the page layout automatically. In this case you should call UpdatePageLayout() before rendering again.

So basically, given my original code, I have to call UpdatePageLayout() after my Writeln()s in order to get the updated page count.

// Get current number of pages int pageCountBefore = builder.Document.PageCount;

for (int i = 0; i < numParagraphs; i++) 
{
    builder.InsertParagraph();
}
// Update the page layout.
builder.Document.UpdatePageLatout();

// Get the number of pages after adding those paragraphs
int pageCountAfter = builder.Document.PageCount;