ArcObjects ITextSymbol.GetTextSize in Python: Why are the out params equal to 0?

Question

This is related to the question I asked earlier about the syntax for this method under Python and comtypes. Now that I know the syntax and am trying to use it, the returned out params are equal to 0. Why is this? Here is my code:

#make TextElement
pTextElement = NewObj(esriCarto.TextElement, esriCarto.ITextElement)
pTextFont = NewObj(stdole.StdFont, stdole.IFontDisp)
pTextFont.Name = 'Arial'
pTextFont.Size = 34.0
pTextSymbol = NewObj(esriDisplay.TextSymbol, esriDisplay.IFormattedTextSymbol)
pTextSymbol.Font = pTextFont
pTextSymbol.HorizontalAlignment = esriDisplay.esriTHACenter
pTextSymbol.VerticalAlignment = esriDisplay.esriTVACenter
txt = 'T>'   #((( hard coded for testing )))
pScrDisp = mxDoc.ActiveView.ScreenDisplay
pDisplay = CType(pScrDisp, esriDisplay.IDisplay)
#Get dimensions of text string
pDisplay.StartDrawing(0, -1)
dblX, dblY = pTextSymbol.GetTextSize(pDisplay.hDC, pDisplay.DisplayTransformation, txt)
pDisplay.FinishDrawing

The out parameters dblX and dblY both equal 0. The hDC and DisplayTransformation inputs are valid. I checked. So, there is something I'm missing. Any insights?

Answer 1

If your script is not running inside the ArcMap's process, I think this is what's happening: The text symbol is created in the python's process, while the display object (map's or layout's screen display) inside the ArcMap's process. Processes in Windows cannot (by design) access GDI resources (like device contexts - the hDC in your code) which do not belong to them. Thus in the context of GetTextSize() call, the passed device context handle is invalid and measurement cannot be performed.

In order words, using IObjectFactory to create the symbols/elements in ArcMap's process (as discussed in other questions) will probably do the trick.