wxWidgets/docs/doxygen/overviews/sizer.h

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// Name:        sizer
// Purpose:     topic overview
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
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/*!

 @page sizer_overview Sizer overview

 Classes: #wxSizer, #wxGridSizer,
 #wxFlexGridSizer, #wxBoxSizer,
 #wxStaticBoxSizer,
 #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 @ref xrc_overview.
 @ref ideabehindsizers_overview
 @ref boxsizerprogramming_overview
 @ref gridsizerprogramming_overview
 @ref flexgridsizerprogramming_overview
 @ref staticboxsizerprogramming_overview
 #CreateButtonSizer


 @section ideabehindsizers The idea behind sizers

 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 @ref boxsizerprogramming_overview.

 @section sizerscommonfeatures Common features

 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:
 @b 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):








 @b 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:







 @b 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:



 @b 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 @e 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:



 Within wxDesigner, this stretch factor gets set from the @e Option menu.

 @section sizershiding Hiding controls using sizers

 You can hide controls contained in sizers the same way you would hide any control,
 using the wxWindow::Show 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 wxSizer::Show.  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.
 @b 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:



 @b wxStaticBoxSizer
 #wxStaticBoxSixer is the same as a wxBoxSizer, but surrounded by a
 static box. Here is a sample:



 @b 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:



 For programming information, see #wxGridSizer.
 @b 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:




 @section boxsizerprogramming Programming with wxBoxSizer

 The basic idea behind a #wxBoxSizer is that windows will most often be laid out in rather
 simple basic geometry, typically in a row or a column or several hierarchies of either.
 As an example, we will construct a dialog that will contain a text field at the top and
 two buttons at the bottom. This can be seen as a top-hierarchy column with the text at
 the top and buttons at the bottom and a low-hierarchy row with an OK button to the left
 and a Cancel button to the right. In many cases (particularly dialogs under Unix and
 normal frames) the main window will be resizable by the user and this change of size
 will have to get propagated to its children. In our case, we want the text area to grow
 with the dialog, whereas the button shall have a fixed size. In addition, there will be
 a thin border around all controls to make the dialog look nice and - to make matter worse -
 the buttons shall be centred as the width of the dialog changes.
 It is the unique feature of a box sizer, that it can grow in both directions (height and
 width) but can distribute its growth in the main direction (horizontal for a row) @e unevenly
 among its children. In our example case, the vertical sizer is supposed to propagate all its
 height changes to only the text area, not to the button area. This is determined by the @e proportion parameter
 when adding a window (or another sizer) to a sizer. It is interpreted
 as a weight factor, i.e. it can be zero, indicating that the window may not be resized
 at all, or above zero. If several windows have a value above zero, the value is interpreted
 relative to the sum of all weight factors of the sizer, so when adding two windows with
 a value of 1, they will both get resized equally much and each half as much as the sizer
 owning them. Then what do we do when a column sizer changes its width? This behaviour is
 controlled by @e flags (the second parameter of the Add() function): Zero or no flag
 indicates that the window will preserve it is original size, wxGROW flag (same as wxEXPAND)
 forces the window to grow with the sizer, and wxSHAPED flag tells the window to change it is
 size proportionally, preserving original aspect ratio.  When wxGROW flag is not used,
 the item can be aligned within available space.  wxALIGN_LEFT, wxALIGN_TOP, wxALIGN_RIGHT,
 wxALIGN_BOTTOM, wxALIGN_CENTER_HORIZONTAL and wxALIGN_CENTER_VERTICAL do what they say.
 wxALIGN_CENTRE (same as wxALIGN_CENTER) is defined as (wxALIGN_CENTER_HORIZONTAL |
 wxALIGN_CENTER_VERTICAL).  Default alignment is wxALIGN_LEFT | wxALIGN_TOP.
 As mentioned above, any window belonging to a sizer may have a border, and it can be specified
 which of the four sides may have this border, using the wxTOP, wxLEFT, wxRIGHT and wxBOTTOM
 constants or wxALL for all directions (and you may also use wxNORTH, wxWEST etc instead). These
 flags can be used in combination with the alignment flags above as the second parameter of the
 Add() method using the binary or operator |. The sizer of the border also must be made known,
 and it is the third parameter in the Add() method. This means, that the entire behaviour of
 a sizer and its children can be controlled by the three parameters of the Add() method.

 @code
 // we want to get a dialog that is stretchable because it
 // has a text ctrl at the top and two buttons at the bottom

 MyDialog::MyDialog(wxFrame *parent, wxWindowID id, const wxString  )
         : wxDialog(parent, id, title, wxDefaultPosition, wxDefaultSize,
                    wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER)
 {
   wxBoxSizer *topsizer = new wxBoxSizer( wxVERTICAL );

   // create text ctrl with minimal size 100x60
   topsizer-Add(
     new wxTextCtrl( this, -1, "My text.", wxDefaultPosition, wxSize(100,60), wxTE_MULTILINE),
     1,            // make vertically stretchable
     wxEXPAND |    // make horizontally stretchable
     wxALL,        //   and make border all around
     10 );         // set border width to 10


   wxBoxSizer *button_sizer = new wxBoxSizer( wxHORIZONTAL );
   button_sizer-Add(
      new wxButton( this, wxID_OK, "OK" ),
      0,           // make horizontally unstretchable
      wxALL,       // make border all around (implicit top alignment)
      10 );        // set border width to 10
   button_sizer-Add(
      new wxButton( this, wxID_CANCEL, "Cancel" ),
      0,           // make horizontally unstretchable
      wxALL,       // make border all around (implicit top alignment)
      10 );        // set border width to 10

   topsizer-Add(
      button_sizer,
      0,                // make vertically unstretchable
      wxALIGN_CENTER ); // no border and centre horizontally

   SetSizerAndFit(topsizer); // use the sizer for layout and size window
                             // accordingly and prevent it from being resized
                             // to smaller size
 }
 @endcode

 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.
 Here's how you'd do the previous example with wxSizerFlags:

 @code
 // we want to get a dialog that is stretchable because it
 // has a text ctrl at the top and two buttons at the bottom

 MyDialog::MyDialog(wxFrame *parent, wxWindowID id, const wxString  )
         : wxDialog(parent, id, title, wxDefaultPosition, wxDefaultSize,
                    wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER)
 {
   wxBoxSizer *topsizer = new wxBoxSizer( wxVERTICAL );

   // create text ctrl with minimal size 100x60 that is horizontally and
   // vertically stretchable with a border width of 10
   topsizer-Add(
     new wxTextCtrl( this, -1, "My text.", wxDefaultPosition, wxSize(100,60), wxTE_MULTILINE),
     wxSizerFlags(1).Align().Expand().Border(wxALL, 10));

   wxBoxSizer *button_sizer = new wxBoxSizer( wxHORIZONTAL );

   //create two buttons that are horizontally unstretchable,
   // with an all-around border with a width of 10 and implicit top alignment
   button_sizer-Add(
      new wxButton( this, wxID_OK, "OK" ),
      wxSizerFlags(0).Align().Border(wxALL, 10));

   button_sizer-Add(
      new wxButton( this, wxID_CANCEL, "Cancel" ),
      wxSizerFlags(0).Align().Border(wxALL, 10));

   //create a sizer with no border and centered horizontally
   topsizer-Add(
      button_sizer,
      wxSizerFlags(0).Center() );

   SetSizerAndFit(topsizer); // use the sizer for layout and set size and hints
 }
 @endcode



 @section gridsizerprogramming Programming with wxGridSizer

 #wxGridSizer is a sizer which lays out its children in a two-dimensional
 table with all table fields having the same size,
 i.e. the width of each field is the width of the widest child,
 the height of each field is the height of the tallest child.

 @section flexgridsizerprogramming Programming with wxFlexGridSizer

 #wxFlexGridSizer is a sizer which lays out its children in a two-dimensional
 table with all table fields in one row having the same
 height and all fields in one column having the same width, but all
 rows or all columns are not necessarily the same height or width as in
 the #wxGridSizer.

 @section staticboxsizerprogramming Programming with wxStaticBoxSizer

 #wxStaticBoxSizer is a sizer derived from wxBoxSizer but adds a static
 box around the sizer. Note that this static box has to be created
 separately.

 @section createbuttonsizer CreateButtonSizer

 As a convenience, CreateButtonSizer ( long flags ) can be used to create a standard button sizer
 in which standard buttons are displayed. The following flags can be passed to this function:


 @code
 wxYES_NO // Add Yes/No subpanel
     wxYES    // return wxID_YES
     wxNO     // return wxID_NO
     wxNO_DEFAULT // make the wxNO button the default, otherwise wxYES or wxOK button will be default

     wxOK     // return wxID_OK
     wxCANCEL // return wxID_CANCEL
     wxHELP   // return wxID_HELP

     wxFORWARD   // return wxID_FORWARD
     wxBACKWARD  // return wxID_BACKWARD
     wxSETUP     // return wxID_SETUP
     wxMORE      // return wxID_MORE
 @endcode

 */