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docs/doxygen/overviews/sizer.h
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docs/doxygen/overviews/sizer.h
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/////////////////////////////////////////////////////////////////////////////
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// Name: sizer
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/*!
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@page sizer_overview Sizer overview
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Classes: #wxSizer, #wxGridSizer,
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#wxFlexGridSizer, #wxBoxSizer,
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#wxStaticBoxSizer,
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#CreateButtonSizer
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Sizers, as represented by the wxSizer class and its descendants in
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the wxWidgets class hierarchy, have become the method of choice to
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define the layout of controls in dialogs in wxWidgets because of
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their ability to create visually appealing dialogs independent of the
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platform, taking into account the differences in size and style of
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the individual controls. Unlike the original wxWidgets Dialog Editor,
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editors such as wxDesigner, DialogBlocks, XRCed and wxWorkshop create dialogs based exclusively on sizers,
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practically forcing the user to create platform independent layouts without compromises.
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The next section describes and shows what can be done with sizers.
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The following sections briefly describe how to program with individual sizer classes.
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For information about the new wxWidgets resource system, which can describe
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sizer-based dialogs, see the @ref xrc_overview.
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@ref ideabehindsizers_overview
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@ref boxsizerprogramming_overview
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@ref gridsizerprogramming_overview
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@ref flexgridsizerprogramming_overview
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@ref staticboxsizerprogramming_overview
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#CreateButtonSizer
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@section ideabehindsizers The idea behind sizers
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The layout algorithm used by sizers in wxWidgets is closely related to layout
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systems in other GUI toolkits, such as Java's AWT, the GTK toolkit or the Qt toolkit. It is
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based upon the idea of individual subwindows reporting their minimal required
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size and their ability to get stretched if the size of the parent window has changed.
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This will most often mean that the programmer does not set the start-up size of
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a dialog, the dialog will rather be assigned a sizer and this sizer
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will be queried about the recommended size. This sizer in turn will query its
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children (which can be normal windows, empty space or other sizers) so that
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a hierarchy of sizers can be constructed. Note that wxSizer does not derive from wxWindow
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and thus does not interfere with tab ordering and requires very few resources compared
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to a real window on screen.
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What makes sizers so well fitted for use in wxWidgets is the fact that every control
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reports its own minimal size and the algorithm can handle differences in font sizes
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or different window (dialog item) sizes on different platforms without problems. For example, if
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the standard font as well as the overall design of Linux/GTK widgets requires more space than
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on Windows, the initial dialog size will automatically be bigger on Linux/GTK than on Windows.
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There are currently five different kinds of sizers available in wxWidgets. Each represents
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either a certain way to lay out dialog items in a dialog or it fulfills a special task
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such as wrapping a static box around a dialog item (or another sizer). These sizers will
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be discussed one by one in the text below. For more detailed information on how to use sizers
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programmatically, please refer to the section @ref boxsizerprogramming_overview.
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@section sizerscommonfeatures Common features
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All sizers are containers, that is, they are used to lay out one dialog item (or several
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dialog items), which they contain. Such items are sometimes referred to as the children
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of the sizer. Independent of how the individual sizers lay out their children, all children
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have certain features in common:
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@b A minimal size: This minimal size is usually identical to
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the initial size of the controls and may either be set explicitly in the wxSize field
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of the control constructor or may be calculated by wxWidgets, typically by setting
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the height and/or the width of the item to -1. Note that only some controls can
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calculate their size (such as a checkbox) whereas others (such as a listbox)
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don't have any natural width or height and thus require an explicit size. Some controls
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can calculate their height, but not their width (e.g. a single line text control):
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@b A border: The border is just empty space and is used to separate dialog items
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in a dialog. This border can either be all around, or at any combination of sides
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such as only above and below the control. The thickness of this border must be set
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explicitly, typically 5 points. The following samples show dialogs with only one
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dialog item (a button) and a border of 0, 5, and 10 pixels around the button:
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@b An alignment: Often, a dialog item is given more space than its minimal size
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plus its border. Depending on what flags are used for the respective dialog
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item, the dialog item can be made to fill out the available space entirely, i.e.
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it will grow to a size larger than the minimal size, or it will be moved to either
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the centre of the available space or to either side of the space. The following
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sample shows a listbox and three buttons in a horizontal box sizer; one button
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is centred, one is aligned at the top, one is aligned at the bottom:
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@b A stretch factor: If a sizer contains more than one child and it is offered
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more space than its children and their borders need, the question arises how to
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distribute the surplus space among the children. For this purpose, a stretch
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factor may be assigned to each child, where the default value of 0 indicates that the child
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will not get more space than its requested minimum size. A value of more than zero
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is interpreted in relation to the sum of all stretch factors in the children
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of the respective sizer, i.e. if two children get a stretch factor of 1, they will
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get half the extra space each @e independent of whether one control has a minimal
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sizer inferior to the other or not. The following sample shows a dialog with
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three buttons, the first one has a stretch factor of 1 and thus gets stretched,
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whereas the other two buttons have a stretch factor of zero and keep their
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initial width:
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Within wxDesigner, this stretch factor gets set from the @e Option menu.
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@section sizershiding Hiding controls using sizers
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You can hide controls contained in sizers the same way you would hide any control,
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using the wxWindow::Show method.
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However, wxSizer also offers a separate method which can tell the sizer not to
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consider that control in its size calculations. To hide a window using the sizer,
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call wxSizer::Show. You must then call Layout on the sizer
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to force an update.
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This is useful when hiding parts of the interface, since you can avoid removing
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the controls from the sizer and having to add them back later.
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Note: This is supported only by wxBoxSizer and wxFlexGridSizer.
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@b wxBoxSizer
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#wxBoxSizer can lay out its children either vertically
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or horizontally, depending on what flag is being used in its constructor.
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When using a vertical sizer, each child can be centered, aligned to the
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right or aligned to the left. Correspondingly, when using a horizontal
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sizer, each child can be centered, aligned at the bottom or aligned at
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the top. The stretch factor described in the last paragraph is used
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for the main orientation, i.e. when using a horizontal box sizer, the
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stretch factor determines how much the child can be stretched horizontally.
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The following sample shows the same dialog as in the last sample,
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only the box sizer is a vertical box sizer now:
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@b wxStaticBoxSizer
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#wxStaticBoxSixer is the same as a wxBoxSizer, but surrounded by a
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static box. Here is a sample:
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@b wxGridSizer
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#wxGridSizer is a two-dimensional sizer. All children are given the
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same size, which is the minimal size required by the biggest child, in
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this case the text control in the left bottom border. Either the number
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of columns or the number or rows is fixed and the grid sizer will grow
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in the respectively other orientation if new children are added:
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For programming information, see #wxGridSizer.
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@b wxFlexGridSizer
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Another two-dimensional sizer derived from
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wxGridSizer. The width of each column and the height of each row
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are calculated individually according to the minimal requirements
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from the respectively biggest child. Additionally, columns and
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rows can be declared to be stretchable if the sizer is assigned
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a size different from the one it requested. The following sample shows
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the same dialog as the one above, but using a flex grid sizer:
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@section boxsizerprogramming Programming with wxBoxSizer
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The basic idea behind a #wxBoxSizer is that windows will most often be laid out in rather
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simple basic geometry, typically in a row or a column or several hierarchies of either.
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As an example, we will construct a dialog that will contain a text field at the top and
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two buttons at the bottom. This can be seen as a top-hierarchy column with the text at
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the top and buttons at the bottom and a low-hierarchy row with an OK button to the left
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and a Cancel button to the right. In many cases (particularly dialogs under Unix and
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normal frames) the main window will be resizable by the user and this change of size
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will have to get propagated to its children. In our case, we want the text area to grow
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with the dialog, whereas the button shall have a fixed size. In addition, there will be
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a thin border around all controls to make the dialog look nice and - to make matter worse -
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the buttons shall be centred as the width of the dialog changes.
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It is the unique feature of a box sizer, that it can grow in both directions (height and
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width) but can distribute its growth in the main direction (horizontal for a row) @e unevenly
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among its children. In our example case, the vertical sizer is supposed to propagate all its
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height changes to only the text area, not to the button area. This is determined by the @e proportion parameter
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when adding a window (or another sizer) to a sizer. It is interpreted
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as a weight factor, i.e. it can be zero, indicating that the window may not be resized
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at all, or above zero. If several windows have a value above zero, the value is interpreted
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relative to the sum of all weight factors of the sizer, so when adding two windows with
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a value of 1, they will both get resized equally much and each half as much as the sizer
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owning them. Then what do we do when a column sizer changes its width? This behaviour is
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controlled by @e flags (the second parameter of the Add() function): Zero or no flag
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indicates that the window will preserve it is original size, wxGROW flag (same as wxEXPAND)
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forces the window to grow with the sizer, and wxSHAPED flag tells the window to change it is
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size proportionally, preserving original aspect ratio. When wxGROW flag is not used,
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the item can be aligned within available space. wxALIGN_LEFT, wxALIGN_TOP, wxALIGN_RIGHT,
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wxALIGN_BOTTOM, wxALIGN_CENTER_HORIZONTAL and wxALIGN_CENTER_VERTICAL do what they say.
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wxALIGN_CENTRE (same as wxALIGN_CENTER) is defined as (wxALIGN_CENTER_HORIZONTAL |
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wxALIGN_CENTER_VERTICAL). Default alignment is wxALIGN_LEFT | wxALIGN_TOP.
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As mentioned above, any window belonging to a sizer may have a border, and it can be specified
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which of the four sides may have this border, using the wxTOP, wxLEFT, wxRIGHT and wxBOTTOM
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constants or wxALL for all directions (and you may also use wxNORTH, wxWEST etc instead). These
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flags can be used in combination with the alignment flags above as the second parameter of the
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Add() method using the binary or operator |. The sizer of the border also must be made known,
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and it is the third parameter in the Add() method. This means, that the entire behaviour of
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a sizer and its children can be controlled by the three parameters of the Add() method.
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@code
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// we want to get a dialog that is stretchable because it
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// has a text ctrl at the top and two buttons at the bottom
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MyDialog::MyDialog(wxFrame *parent, wxWindowID id, const wxString )
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: wxDialog(parent, id, title, wxDefaultPosition, wxDefaultSize,
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wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER)
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{
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wxBoxSizer *topsizer = new wxBoxSizer( wxVERTICAL );
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// create text ctrl with minimal size 100x60
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topsizer-Add(
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new wxTextCtrl( this, -1, "My text.", wxDefaultPosition, wxSize(100,60), wxTE_MULTILINE),
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1, // make vertically stretchable
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wxEXPAND | // make horizontally stretchable
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wxALL, // and make border all around
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10 ); // set border width to 10
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wxBoxSizer *button_sizer = new wxBoxSizer( wxHORIZONTAL );
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button_sizer-Add(
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new wxButton( this, wxID_OK, "OK" ),
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0, // make horizontally unstretchable
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wxALL, // make border all around (implicit top alignment)
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10 ); // set border width to 10
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button_sizer-Add(
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new wxButton( this, wxID_CANCEL, "Cancel" ),
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0, // make horizontally unstretchable
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wxALL, // make border all around (implicit top alignment)
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10 ); // set border width to 10
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topsizer-Add(
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button_sizer,
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0, // make vertically unstretchable
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wxALIGN_CENTER ); // no border and centre horizontally
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SetSizerAndFit(topsizer); // use the sizer for layout and size window
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// accordingly and prevent it from being resized
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// to smaller size
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}
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@endcode
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Note that the new way of specifying flags to wxSizer is via #wxSizerFlags. This class greatly eases the burden of passing flags to a wxSizer.
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Here's how you'd do the previous example with wxSizerFlags:
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@code
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// we want to get a dialog that is stretchable because it
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// has a text ctrl at the top and two buttons at the bottom
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MyDialog::MyDialog(wxFrame *parent, wxWindowID id, const wxString )
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: wxDialog(parent, id, title, wxDefaultPosition, wxDefaultSize,
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wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER)
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{
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wxBoxSizer *topsizer = new wxBoxSizer( wxVERTICAL );
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// create text ctrl with minimal size 100x60 that is horizontally and
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// vertically stretchable with a border width of 10
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topsizer-Add(
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new wxTextCtrl( this, -1, "My text.", wxDefaultPosition, wxSize(100,60), wxTE_MULTILINE),
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wxSizerFlags(1).Align().Expand().Border(wxALL, 10));
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wxBoxSizer *button_sizer = new wxBoxSizer( wxHORIZONTAL );
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//create two buttons that are horizontally unstretchable,
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// with an all-around border with a width of 10 and implicit top alignment
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button_sizer-Add(
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new wxButton( this, wxID_OK, "OK" ),
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wxSizerFlags(0).Align().Border(wxALL, 10));
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button_sizer-Add(
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new wxButton( this, wxID_CANCEL, "Cancel" ),
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wxSizerFlags(0).Align().Border(wxALL, 10));
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//create a sizer with no border and centered horizontally
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topsizer-Add(
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button_sizer,
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wxSizerFlags(0).Center() );
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SetSizerAndFit(topsizer); // use the sizer for layout and set size and hints
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}
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@endcode
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@section gridsizerprogramming Programming with wxGridSizer
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#wxGridSizer is a sizer which lays out its children in a two-dimensional
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table with all table fields having the same size,
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i.e. the width of each field is the width of the widest child,
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the height of each field is the height of the tallest child.
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@section flexgridsizerprogramming Programming with wxFlexGridSizer
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#wxFlexGridSizer is a sizer which lays out its children in a two-dimensional
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table with all table fields in one row having the same
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height and all fields in one column having the same width, but all
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rows or all columns are not necessarily the same height or width as in
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the #wxGridSizer.
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@section staticboxsizerprogramming Programming with wxStaticBoxSizer
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#wxStaticBoxSizer is a sizer derived from wxBoxSizer but adds a static
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box around the sizer. Note that this static box has to be created
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separately.
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@section createbuttonsizer CreateButtonSizer
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As a convenience, CreateButtonSizer ( long flags ) can be used to create a standard button sizer
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in which standard buttons are displayed. The following flags can be passed to this function:
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@code
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wxYES_NO // Add Yes/No subpanel
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wxYES // return wxID_YES
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wxNO // return wxID_NO
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wxNO_DEFAULT // make the wxNO button the default, otherwise wxYES or wxOK button will be default
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wxOK // return wxID_OK
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wxCANCEL // return wxID_CANCEL
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wxHELP // return wxID_HELP
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wxFORWARD // return wxID_FORWARD
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wxBACKWARD // return wxID_BACKWARD
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wxSETUP // return wxID_SETUP
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wxMORE // return wxID_MORE
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@endcode
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*/
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