Funny Little Thing (Solved)

Next day second thoughts: While as noted, QTextDocument inherits from QObject and as such has no font property, it does for no obvious reason have a defaultFont property which it imposes on any Q[Plain]TextEdit to which it is connected. This completely violates the Model/View scheme, the Model imposing a presentation feature on the View, but there it is. Furthermore, it can't be overridden! As I note below, when I interrogate the edit widget for its font().family and font().pointSize, it happily reports the values I'd set. But what it displays is its document's default font, if the document is connected second. So fie on ye, Qt designer.

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OK, here's an oddity in Qt. I'm working on the editview, a panel mainly containing a QPlainTextEdit that is pretty much the heart of PPQT. But the editor is the "view" and its "model" or repository of data is a QTextDocument. Most of the GUI initialization is handled by the code generated from the Designer. But the __init__ for the editview has to do two key things. Well, there will be lots more, hooking up signals, setting up the syntax highlighter, blah blah, but in its rudimentary state, two things:

• Set its fonts
• Set its document to the edit model

Item two is pretty simple. The parent Book is the repository of all knowledge, so it just does self.Editor.setDocument(self.my_book.get_edit_model()).

Setting the fonts is slightly more work. This is looking ahead to when the user will be able to tell the main window, I want to choose a different UI font, the default font used in most labels and buttons, or I want to choose a different edit font, the had-better-be-monospaced font used only in the editview(s) and one or two other places like the Find text string.

So there can be multiple Books open each with its editview, and up in the main window the user says, "Let's use Courier!" Main window will emit a signal, and any widget that cares better catch it and change fonts.

Also, at open time when setting up a new editview, we want to restore the font size the user had last time the book was open. In version 1, with only one book, that was a global setting, but now there can be multiple documents with potentially each editview zoomed to a different font size! Just one of the many, many features affected by multiple documents.

Anyway, while initializing, the editview needs to ask its Book for the font size and also ask the global font module for the proper font, and set that family/size combo in the QPlainTextEdit. No biggie, a simple method that is called in init. or by the font-change signal:

    def set_fonts(self):
        general = fonts.get_general() # UI font at default size
        self.setFont(general) # set self, propogates to children
        mono = fonts.get_fixed(self.my_book.get_font_size())
        self.Editor.setFont(mono) # the editor is monospaced

This story is going somewhere, really. OK, so the editview initialized like this:

        self.set_fonts()
        self.Editor.setDocument(self.my_book.get_edit_model())

And it didn't work. When it displayed, all the labels would be in the system default font (Lucida Grande 13pt) but so would the edit widget be. I put in a debug print to query the edit widget's font and display it. It happily reported, "I'm using Liberation Mono 16 just like you said, boss", but when I typed in the edit window, it came out in Lucida. I set the parent widget to the mono font, and all the labels displayed in mono but the damn edit text was still Lucida!

After wasting a couple of hours on this, it occurred to me the QTextDocument might be the villain. I reversed the init to

        self.Editor.setDocument(self.document)
        self.set_fonts()

And it worked, the edit text is now in the chosen mono font. WTF? Reviewing the doc for QTextDocument, it inherits from QObject not QWidget, so it doesn't even have a font property. Yet somehow, the call to setDocument() undid the work of a preceding call to setFont(). Maybe changing the document is so basic to the edit widget that it treats it as a reset. Whatever. In my application, I only set the document once. As long as it happens first, all is well.