The layout algorithm used by sizers in wxWidgets is closely related to layout systems in other GUI toolkits, such as Java's AWT, the GTK toolkit or the Qt toolkit. It is based upon the idea of individual subwindows reporting their minimal required size and their ability to get stretched if the size of the parent window has changed. This will most often mean that the programmer does not set the start-up size of a dialog, the dialog will rather be assigned a sizer and this sizer will be queried about the recommended size. This sizer in turn will query its children (which can be normal windows, empty space or other sizers) so that a hierarchy of sizers can be constructed. Note that wxSizer does not derive from wxWindow and thus does not interfere with tab ordering and requires very few resources compared to a real window on screen.
What makes sizers so well fitted for use in wxWidgets is the fact that every control reports its own minimal size and the algorithm can handle differences in font sizes or different window (dialog item) sizes on different platforms without problems. For example, if the standard font as well as the overall design of Linux/GTK widgets requires more space than on Windows, the initial dialog size will automatically be bigger on Linux/GTK than on Windows.
There are currently five different kinds of sizers available in wxWidgets. Each represents either a certain way to lay out dialog items in a dialog or it fulfills a special task such as wrapping a static box around a dialog item (or another sizer). These sizers will be discussed one by one in the text below. For more detailed information on how to use sizers programmatically, please refer to the section Programming with Sizers.