Layout Basics

Before taking the plunge into the world of sizers, let's review where you might need to program layout behavior and what options you have.

A simple case is where you have a frame with a single window inside the client area. This is so simple that wxWidgets does the layout itself, fitting the child window to the size of the frame client area. For each frame, wxWidgets also manages the menu bar, one toolbar, and one status bar if they have been associated with the frame. If you need two toolbars, then you have to manage at least one of them yourself. If you have more than one child window in the client area, then wxWidgets expects you to manage them explicitly. You can do this with an OnSize event handler and calculate the position and size for each window and then set them. Or, you can use sizers. Similarly, if you create a custom control that consists of several child windows, you need to arrange for the child windows to resize appropriately when the overall control is resized.

Most applications have custom dialogs, sometimes dozens of them. The dialogs may be resizable, in which case the layout should look sensible even when the dialog is much larger than the initial size. The language may be changed, making some elements much larger or smaller than in the default language. If you had to program a hundred resize-friendly dialogs by hand, even with sizers, it would be almost impossibly daunting, so it's fortunate that editors are available to make this task simpleeven a pleasure.

If (and when!) you choose to use sizers, you need to decide how you will create and deploy them. You or your dialog editor can create code in C++ or another language, or you can use XRC files, which are a declarative XML specification of the sizer layout. XRC files can be loaded dynamically or embedded in the executable by compiling them into C++ files with the utility wxrc. Most dialog editors can generate both code and XRC files. Your choice of code or XRC may be a matter of taste; perhaps you prefer to separate the layout from the class, or maybe you prefer the additional flexibility of tweaking the C++ code and the immediacy of having it in the same file as the class.

The next section describes the principles behind sizers, and the following sections describe how to program with individual sizer classes.