tsizer.tex

很牛的GUI源码wxWidgets-2.8.0.zip 可在多种平台下运行.

\section{Sizer overview}\label{sizeroverview}

Classes: \helpref{wxSizer}{wxsizer}, \helpref{wxGridSizer}{wxgridsizer}, 
\helpref{wxFlexGridSizer}{wxflexgridsizer}, \helpref{wxBoxSizer}{wxboxsizer}, 
\helpref{wxStaticBoxSizer}{wxstaticboxsizer}, 
\helpref{CreateButtonSizer}{createbuttonsizer}

Sizers, as represented by the wxSizer class and its descendants in
the wxWidgets class hierarchy, have become the method of choice to
define the layout of controls in dialogs in wxWidgets because of
their ability to create visually appealing dialogs independent of the
platform, taking into account the differences in size and style of
the individual controls. Unlike the original wxWidgets Dialog Editor,
editors such as wxDesigner, DialogBlocks, XRCed and wxWorkshop create dialogs based exclusively on sizers,
practically forcing the user to create platform independent layouts without compromises.

The next section describes and shows what can be done with sizers.
The following sections briefly describe how to program with individual sizer classes.

For information about the new wxWidgets resource system, which can describe
sizer-based dialogs, see the \helpref{XML-based resource system overview}{xrcoverview}.

\subsection{The idea behind sizers}\label{ideabehindsizers}

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 \helpref{Programming with Sizers}{boxsizerprogramming}.

\subsubsection{Common features}\label{sizerscommonfeatures}

All sizers are containers, that is, they are used to lay out one dialog item (or several
dialog items), which they contain. Such items are sometimes referred to as the children
of the sizer. Independent of how the individual sizers lay out their children, all children
have certain features in common:

{\bf A minimal size:} This minimal size is usually identical to
the initial size of the controls and may either be set explicitly in the wxSize field
of the control constructor or may be calculated by wxWidgets, typically by setting
the height and/or the width of the item to -1. Note that only some controls can
calculate their size (such as a checkbox) whereas others (such as a listbox)
don't have any natural width or height and thus require an explicit size. Some controls
can calculate their height, but not their width (e.g. a single line text control):

\newcommand{\myimage}[1]{\mbox{\image{0cm;0cm}{#1}}}

\begin{center}
\myimage{sizer03.eps}\gifsep
\myimage{sizer04.eps}\gifsep
\myimage{sizer05.eps}
\end{center}

{\bf A border:} The border is just empty space and is used to separate dialog items
in a dialog. This border can either be all around, or at any combination of sides
such as only above and below the control. The thickness of this border must be set
explicitly, typically 5 points. The following samples show dialogs with only one
dialog item (a button) and a border of 0, 5, and 10 pixels around the button:

\begin{center}
\myimage{sizer00.eps}\gifsep
\myimage{sizer01.eps}\gifsep
\myimage{sizer02.eps}
\end{center}

{\bf An alignment:} Often, a dialog item is given more space than its minimal size
plus its border. Depending on what flags are used for the respective dialog
item, the dialog item can be made to fill out the available space entirely, i.e.
it will grow to a size larger than the minimal size, or it will be moved to either
the centre of the available space or to either side of the space. The following
sample shows a listbox and three buttons in a horizontal box sizer; one button
is centred, one is aligned at the top, one is aligned at the bottom:

\begin{center}
\myimage{sizer06.eps}
\end{center}

{\bf A stretch factor:} If a sizer contains more than one child and it is offered
more space than its children and their borders need, the question arises how to
distribute the surplus space among the children. For this purpose, a stretch
factor may be assigned to each child, where the default value of 0 indicates that the child
will not get more space than its requested minimum size. A value of more than zero
is interpreted in relation to the sum of all stretch factors in the children
of the respective sizer, i.e. if two children get a stretch factor of 1, they will
get half the extra space each {\it independent of whether one control has a minimal
sizer inferior to the other or not}. The following sample shows a dialog with
three buttons, the first one has a stretch factor of 1 and thus gets stretched,
whereas the other two buttons have a stretch factor of zero and keep their
initial width:

\begin{center}
\myimage{sizer07.eps}
\end{center}

Within wxDesigner, this stretch factor gets set from the {\it Option} menu.

\subsubsection{Hiding controls using sizers}\label{sizershiding}

You can hide controls contained in sizers the same way you would hide any control,
using the \helpref{wxWindow::Show}{wxwindowshow} method.

However, wxSizer also offers a separate method which can tell the sizer not to 
consider that control in its size calculations.  To hide a window using the sizer,
call \helpref{wxSizer::Show}{wxsizershow}.  You must then call Layout on the sizer 
to force an update.

This is useful when hiding parts of the interface, since you can avoid removing
the controls from the sizer and having to add them back later.

Note: This is supported only by wxBoxSizer and wxFlexGridSizer.

\wxheading{wxBoxSizer}

\helpref{wxBoxSizer}{wxboxsizer} can lay out its children either vertically
or horizontally, depending on what flag is being used in its constructor.
When using a vertical sizer, each child can be centered, aligned to the
right or aligned to the left. Correspondingly, when using a horizontal
sizer, each child can be centered, aligned at the bottom or aligned at
the top. The stretch factor described in the last paragraph is used
for the main orientation, i.e. when using a horizontal box sizer, the
stretch factor determines how much the child can be stretched horizontally.
The following sample shows the same dialog as in the last sample,
only the box sizer is a vertical box sizer now:

\begin{center}
\myimage{sizer08.eps}
\end{center}

\wxheading{wxStaticBoxSizer}

\helpref{wxStaticBoxSixer}{wxstaticboxsizer} is the same as a wxBoxSizer, but surrounded by a
static box. Here is a sample:

\begin{center}
\myimage{sizer09.eps}
\end{center}

\wxheading{wxGridSizer}

\helpref{wxGridSizer}{wxgridsizer} is a two-dimensional sizer. All children are given the
same size, which is the minimal size required by the biggest child, in
this case the text control in the left bottom border. Either the number
of columns or the number or rows is fixed and the grid sizer will grow
in the respectively other orientation if new children are added:

\begin{center}
\myimage{sizer10.eps}
\end{center}

For programming information, see \helpref{wxGridSizer}{wxgridsizer}.

\wxheading{wxFlexGridSizer}

Another two-dimensional sizer derived from
wxGridSizer. The width of each column and the height of each row
are calculated individually according to the minimal requirements
from the respectively biggest child. Additionally, columns and
rows can be declared to be stretchable if the sizer is assigned
a size different from the one it requested. The following sample shows
the same dialog as the one above, but using a flex grid sizer: