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Canvas And Its Callbacks In OO Code
I learn to use 2 different types of Canvas callbacks in the <a href=http://www.bigbold.com/snippets/posts/show/730>last snippet</a>. Typically, when I wrote a non-OO code, I will use
app.body = c = Canvas()
where I already had
from appuifw import *
The shortcoming is that I need to define callbacks first, then pass it to the constructor c = Canvas(redraw_callback, event_callback) By using OO, the canvas is created in __init__() and it can access other methods that come later in the code. In this case, I use Canvas(self.update) which means that the self.update will be used to redraw screen. The secode way to use callback is Canvas.bind() method. I have always been using this approach to binding any event callback to a canvas. In some case, the event_callback in the constructor maybe more elegant, though. Notice my use of
Here I can bind the select key to self.toggle whose definition will follow. This is more convenient than having to define it first. So, I think OO code is easier to write in this way. I also use class variables instead of instance variables. I found declaring it outside __init__() is more natural and similar to my previous non-OO approach. (still easy to read, with variable & def declarations) When I write self.myvar inside __init__(), I feel the code is somewhat bloated. The class will have only 1 instance anyway.