How to learn wxWidgets programming

The following is a response by Edward Ream to a common question, "What's the best way to learn wxWidgets [and C++]?".

Date: Sun, 04 Jun 2000 14:37:06 -0500
From: "Edward K. Ream" <edream@tds.net>
To: wx-users@wxwidgets.org
Subject: Re: [wx-users] How to learn using wx-windows
Reply-To: wx-users@wxwidgets.org

> Reading the Linux Journal article on wxpython, and having used wxclips
> I got interested in wxwidgets as a development interface. However, the
> programming experience I got is old, and from a former generation (For-
> tran). I'd like to refresh my experience and start in C++. Will
> wx-windows be a very high step to take?

I'm new to wxWidgets myself, but I'd like to answer this question anyway. In the past two years I've learned two similar frameworks (Apple's Yellow Box, aka NextStep/OpenStep and Borland's C++ Builder/Delphi) and last year I became a C++ enthusiast after 20 years of using C.

About C++.

The major Aha for me was that the complexity of C++ doesn't matter in practice. What _does_ matter is that C++ allows you to do simple things simply, more simply than C. With a system like wxWidgets you will be creating objects and then using those objects to call methods. So don't be afraid of C++: you'll only be using the easy tip of the iceberg.

Besides the C++ Programming Language, by Bjarne Stroustrup, the "official" guide to C++, I highly recommend Inside the C++ Object Model, by Stanley B. Lippman. (Lippman was one of the C++ honchos at Bell Labs.) This book will tell you what _not_ to do, as well as why everything in C++ is as it is. If you are confused by anything in C++, Lippman's book is the cure.

About applications frameworks.

Application frameworks such as wxWidgets are organized around a set of cooperating classes. Take a look at the main application class, wxApp, some frame and panel classes, graphics classes, menu classes, control classes, etc. In general, to do anything in a framework involves creating an object of the specified type, then doing something with that object.

For example, suppose you want to create a menu bar. A menu bar is composed of a single menu bar object of type(class) wxMenuBar that contains menu objects of type wxMenu. Each menu object contains menu item objects of type wxMenuItem. So you create the menu bar object, then create all the menu objects (creating the menu item objects along the way) and finally "attach" the menu objects to the menu bar object using a call to the wxMenuBar::Append method.

As an overview I would look at the "Alphabetical class reference" section of the reference manual. I find the HTML version to be the easiest to use: you can browse very quickly through it. Here's how to read this (very large) reference:

1. Get an overview of the kinds of classes involved. The class names will tell you a lot about what each class does. Open some of the classes, in particular, wxApp (the main application object), wxFrame, wxControl (the base class for all controls) and one or two controls, like wxButton.
2. When scanning a class for the first several times, read the introductory remarks and quickly scan the list of methods of the class to get a general idea about what kinds of operations can be done to objects of the class. You are not looking for detail at this stage, just for the big picture. In particular, what classes exist and how do they work together.
3. Pay particular attention to the classes from which a class is derived. For example, a button (an object of type wxButton) is derived from the wxControl, wxWindow, wxEvtHandler and wxObject classes. What does this mean? It means that a button _is_ a control, and a button _is_ a window, and a button _is_ an event handler and a button _is_ an object. So you must understand the parent classes of an object to understand the object itself. For example, if b is a button you can invoke b.m for any of method m of the wxControl, wxWindow, wxEvtHandler or wxObject classes. You are not limited to just the methods of wxButton! This is one of the keys of object oriented programming.

Some other tips:

Read some sample code. You will find that almost none of the C++ language is actually being used; it's just endlessly creating objects and then calling methods using those objects.

Learn as much as you can about the String class; after using a good String class you'll never want to use C's string functions again. wxWidgets contains other nifty utility classes as well.

The application class, wxApp, contains the main event loop. Learn about event handling and event tables (reading sample code will help). Almost everything in this kind of application framework happens as the result of an event and your app is essentially doing nothing but responding to events. Having the event loop written for you is a major, major benefit.

I hope this helps. Perhaps we can work together in learning about wxWidgets. Please feel free to ask me any questions you might have. If I've made any blunders in this posting I hope the wxWidgets experts will correct me gently.

Edward
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Edward K. Ream email: edream@tds.net
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