I want to write a Python app that uses GTK (via gi.repository) to display a textual view of a huge amount of data. (Specifically, disassembled instructions from a program, similar to what IDA shows.)
I thought this should be fairly simple: use an ordinary GtkTextView, and a custom subclass of GtkTextBuffer which will handle the "give me some text" request, generate some text (disassemble some instructions) and some tags (for colouring, formatting, etc) and return them.
The issue is I can't find any information on how to subclass GtkTextBuffer in this way, to provide the text myself. I've tried just implementing the get_text and get_slice methods in my subclass, but they seem to never be called. It seems like the only thing I can do is use a standard GtkTextBuffer and the set_text method, and try somehow to keep track of the cursor position and number of lines to display, but this seems entirely opposite to how MVC should work. There are potentially millions of lines, so generating all text in advance is infeasible.
I'm using Python 3.4 and GTK3.
Gtk.TextBuffer is from an external library that isn't written in Python. You've run into one limitation of that situation. With most Python libraries you can subclass their classes or monkeypatch their APIs however you like. GTK's C code, on the other hand, is unaware that it's being used from Python, and as you have noticed, completely ignores your overridden get_text() and get_slice() methods.
GTK's classes additionally have the limitation that you can only override methods that have been declared "virtual". Here's how that translates into Python: you can see a list of virtual methods in the Python GI documentation (example for Gtk.TextBuffer). These methods all start with do_ and are not meant to be called from your program, only overridden. Python GI will make the GTK code aware of these overrides, so that when you override, e.g., do_insert_text() and subsequently call insert_text(), the chain of calls will look something like this:
insert_text()
gtk_text_buffer_insert_text()
GtkTextBufferClass->insert_text() (internal virtual method)
do_insert_text()Unfortunately, as you can see from the documentation that I linked above, get_text() and get_slice() are not virtual, so you can't override them in a subclass.
You might be able to achieve your aim by wrapping one TextBuffer (which contains the entirety of your disassembled instructions) in another (which contains an excerpt, and is actually hooked up to the text view.) You could set marks in the first text buffer to show where the excerpt should begin or end, and connect signals such that when the text in the first text buffer changes, or the marks change, then the text between the marks is copied to the second text buffer.