Dynamic Spacer in ReportLab

Question

I'm automatically generating a PDF-file with Platypus that has dynamic content.

This means that it might happen that the length of the text content (which is directly at the bottom of the pdf-file) may vary.

However, it might happen that a page break is done in cases where the content is too long. This is because i use a "static" spacer:

s = Spacer(width=0, height=23.5*cm) 

as i always want to have only one page, I somehow need to dynamically set the height of the Spacer, so that the "rest" of the space that is left on the page is taken by the Spacer as its height.

Now, how do i get the "rest" of height that is left on my page?

Answer 1

As far as i can see you want to have footer, right?

Then you should do it like:

def _laterPages(canvas, doc):
    canvas.drawImage(os.path.join(settings.PROJECT_ROOT, 'templates/documents/pics/footer.png'), left_margin, bottom_margin - 0.5*cm, frame_width,  0.5*cm)

doc = BaseDocTemplate(filename,showBoundary=False)
doc.multiBuild(flowble elements, _firstPage, _laterPages)

Answer 2

I sniffed around in the reportlab library a bit and found the following: Basically, I decided to use a frame into which the flowables will be printed. f._aH returns the height of the Frame (we could also calculate this by hand). Subtracting the heights of the other two flowables, which we get through wrap, we get the remaining height which is the height of the Spacer.

elements.append(Flowable1)
elements.append(Flowable2)

c = Canvas(path)
f = Frame(fx, fy,fw,fh,showBoundary=0)

# compute the available height for the spacer
sheight = f._aH - (Flowable1.wrap(f._aW,f._aH)[1] + Flowable2.wrap(f._aW,f._aH)[1])

# create spacer
s = Spacer(width=0, height=sheight)

# insert the spacer between the two flowables
elements.insert(1,s)

# create a frame from the list of elements
f.addFromList(elements,c)

c.save()

tested and works fine.