revised topic overviews (letters g,h)

[wxWidgets.git] / docs / doxygen / overviews / docview.h

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

 @page overview_docview Document/view overview

 Classes: #wxDocument, #wxView, #wxDocTemplate, #wxDocManager, #wxDocParentFrame, 
          #wxDocChildFrame, #wxDocMDIParentFrame, #wxDocMDIChildFrame,
          #wxCommand, #wxCommandProcessor

 The document/view framework is found in most application frameworks, because it
 can dramatically simplify the code required to build many kinds of application.

 The idea is that you can model your application primarily in terms of @e documents to store data
 and provide interface-independent operations upon it, and @e views to visualise and manipulate
 the data. Documents know how to do input and output given stream objects, and views are responsible
 for taking input from physical windows and performing the manipulation on the document data.

 If a document's data changes, all views should be updated to reflect the change.
 The framework can provide many user-interface elements based on this model.

 Once you have defined your own classes and the relationships between them, the framework 
 takes care of popping up file selectors, opening and closing files, asking the user to save
 modifications, routing menu commands to appropriate (possibly default) code, even
 some default print/preview functionality and support for command undo/redo.

 The framework is highly modular, allowing overriding and replacement of functionality
 and objects to achieve more than the default behaviour.

 These are the overall steps involved in creating an application based on the 
 document/view framework:

 @li Define your own document and view classes, overriding a minimal set of
     member functions e.g. for input/output, drawing and initialization.
 @li Define any subwindows (such as a scrolled window) that are needed for the view(s).
     You may need to route some events to views or documents, for example OnPaint needs 
     to be routed to wxView::OnDraw.
 @li Decide what style of interface you will use: Microsoft's MDI (multiple
     document child frames surrounded by an overall frame), SDI (a separate, unconstrained frame
     for each document), or single-window (one document open at a time, as in Windows Write).
 @li Use the appropriate wxDocParentFrame and wxDocChildFrame classes. Construct an instance
     of wxDocParentFrame in your wxApp::OnInit, and a wxDocChildFrame (if not single-window) when
     you initialize a view. Create menus using standard menu ids (such as wxID_OPEN, wxID_PRINT).
 @li Construct a single wxDocManager instance at the beginning of your wxApp::OnInit, and then
     as many wxDocTemplate instances as necessary to define relationships between documents and
     views. For a simple application, there will be just one wxDocTemplate.

 If you wish to implement Undo/Redo, you need to derive your own class(es) from wxCommand
 and use wxCommandProcessor::Submit instead of directly executing code. The framework will
 take care of calling Undo and Do functions as appropriate, so long as the wxID_UNDO and
 wxID_REDO menu items are defined in the view menu.

 Here are a few examples of the tailoring you can do to go beyond the default framework
 behaviour:

 @li Override wxDocument::OnCreateCommandProcessor to define a different Do/Undo strategy,
     or a command history editor.
 @li Override wxView::OnCreatePrintout to create an instance of a derived #wxPrintout
     class, to provide multi-page document facilities.
 @li Override wxDocManager::SelectDocumentPath to provide a different file selector.
 @li Limit the maximum number of open documents and the maximum number of undo commands.

 Note that to activate framework functionality, you need to use some or all of
 the wxWidgets @ref predefinedids_overview in your menus.

 @beginWxPerlOnly
 The document/view framework is available in wxPerl. To use it,
 you will need the following statements in your application code:

 @code
 use Wx::DocView;
 use Wx ':docview';   # import constants (optional)
 @endcode
 @endWxPerlOnly

 @li @ref overview_docview_wxdoc
 @li @ref overview_docview_wxview
 @li @ref overview_docview_wxdoctemplate
 @li @ref overview_docview_wxdocmanager
 @li @ref overview_docview_wxcommand
 @li @ref overview_docview_wxcommandproc
 @li @ref overview_docview_filehistory
 @li @ref overview_docview_predefid


 <hr>


 @section overview_docview_wxdoc wxDocument overview

 Class: #wxDocument

 The wxDocument class can be used to model an application's file-based
 data. It is part of the document/view framework supported by wxWidgets,
 and cooperates with the #wxView, #wxDocTemplate and #wxDocManager classes.
 Using this framework can save a lot of routine user-interface programming,
 since a range of menu commands -- such as open, save, save as -- are supported
 automatically.

 The programmer just needs to define a minimal set of classes and member functions
 for the framework to call when necessary. Data, and the means to view and edit
 the data, are explicitly separated out in this model, and the concept of multiple
 @e views onto the same data is supported.

 Note that the document/view model will suit many but not all styles of application.
 For example, it would be overkill for a simple file conversion utility, where there
 may be no call for @e views on @e documents or the ability to open, edit and save
 files. But probably the majority of applications are document-based.

 See the example application in @c samples/docview.
 To use the abstract wxDocument class, you need to derive a new class and override
 at least the member functions SaveObject and LoadObject. SaveObject and
 LoadObject will be called by the framework when the document needs to be saved
 or loaded.

 Use the macros DECLARE_DYNAMIC_CLASS and IMPLEMENT_DYNAMIC_CLASS in order
 to allow the framework to create document objects on demand. When you create
 a #wxDocTemplate object on application initialization, you
 should pass CLASSINFO(YourDocumentClass) to the wxDocTemplate constructor
 so that it knows how to create an instance of this class.

 If you do not wish to use the wxWidgets method of creating document
 objects dynamically, you must override wxDocTemplate::CreateDocument
 to return an instance of the appropriate class.



 @section overview_docview_wxview wxView overview

 Class: #wxView

 The wxView class can be used to model the viewing and editing component of
 an application's file-based data. It is part of the document/view framework 
 supported by wxWidgets, and cooperates with the #wxDocument, #wxDocTemplate
 and #wxDocManager classes.

 See the example application in @c samples/docview.

 To use the abstract wxView class, you need to derive a new class and override
 at least the member functions OnCreate, OnDraw, OnUpdate and OnClose. You will probably
 want to respond to menu commands from the frame containing the view.

 Use the macros DECLARE_DYNAMIC_CLASS and IMPLEMENT_DYNAMIC_CLASS in order
 to allow the framework to create view objects on demand. When you create
 a #wxDocTemplate object on application initialization, you
 should pass CLASSINFO(YourViewClass) to the wxDocTemplate constructor
 so that it knows how to create an instance of this class.

 If you do not wish to use the wxWidgets method of creating view
 objects dynamically, you must override wxDocTemplate::CreateView
 to return an instance of the appropriate class.



 @section overview_docview_wxdoctemplate wxDocTemplate overview

 Class: #wxDocTemplate

 The wxDocTemplate class is used to model the relationship between a
 document class and a view class. The application creates a document
 template object for each document/view pair. The list of document
 templates managed by the wxDocManager instance is used to create
 documents and views. Each document template knows what file filters
 and default extension are appropriate for a document/view combination,
 and how to create a document or view.

 For example, you might write a small doodling application that can load
 and save lists of line segments. If you had two views of the data -- graphical,
 and a list of the segments -- then you would create one document class DoodleDocument,
 and two view classes (DoodleGraphicView and DoodleListView). You would also
 need two document templates, one for the graphical view and another for the
 list view. You would pass the same document class and default file extension to both
 document templates, but each would be passed a different view class. When
 the user clicks on the Open menu item, the file selector is displayed
 with a list of possible file filters -- one for each wxDocTemplate. Selecting
 the filter selects the wxDocTemplate, and when a file is selected, that template 
 will be used for creating a document and view.

 For the case where an application has one document type and one view type,
 a single document template is constructed, and dialogs will be appropriately
 simplified.

 wxDocTemplate is part of the document/view framework supported by wxWidgets,
 and cooperates with the #wxView, #wxDocument and #wxDocManager classes.

 See the example application in @c samples/docview.

 To use the wxDocTemplate class, you do not need to derive a new class.
 Just pass relevant information to the constructor including CLASSINFO(YourDocumentClass) 
 and CLASSINFO(YourViewClass) to allow dynamic instance creation.

 If you do not wish to use the wxWidgets method of creating document
 objects dynamically, you must override wxDocTemplate::CreateDocument
 and wxDocTemplate::CreateView to return instances of the appropriate class.

 @note The document template has nothing to do with the C++ template construct.



 @section overview_docview_wxdocmanager wxDocManager overview

 Class: #wxDocManager

 The wxDocManager class is part of the document/view framework supported by wxWidgets,
 and cooperates with the #wxView, #wxDocument and #wxDocTemplate classes.

 A wxDocManager instance coordinates documents, views and document templates. 
 It keeps a list of document and template instances, and much functionality is routed 
 through this object, such as providing selection and file dialogs. 
 The application can use this class 'as is' or derive a class and override some members 
 to extend or change the functionality.

 Create an instance of this class near the beginning of your application initialization,
 before any documents, views or templates are manipulated.

 There may be multiple wxDocManager instances in an application.
 See the example application in @c samples/docview.



 @section overview_docview_wxcommand wxCommand overview

 Classes: #wxCommand, #wxCommandProcessor

 wxCommand is a base class for modelling an application command,
 which is an action usually performed by selecting a menu item, pressing
 a toolbar button or any other means provided by the application to
 change the data or view.

 Instead of the application functionality being scattered around
 switch statements and functions in a way that may be hard to
 read and maintain, the functionality for a command is explicitly represented
 as an object which can be manipulated by a framework or application.

 When a user interface event occurs, the application @e submits a command
 to a #wxCommandProcessor object to execute and store.

 The wxWidgets document/view framework handles Undo and Redo by use of
 wxCommand and wxCommandProcessor objects. You might find further uses
 for wxCommand, such as implementing a macro facility that stores, loads
 and replays commands.

 An application can derive a new class for every command, or, more likely, use
 one class parameterized with an integer or string command identifier.



 @section overview_docview_wxcommandproc wxCommandProcessor overview

 Classes: #wxCommandProcessor, #wxCommand

 wxCommandProcessor is a class that maintains a history of wxCommand
 instances, with undo/redo functionality built-in. Derive a new class from this
 if you want different behaviour.



 @section overview_docview_filehistory wxFileHistory overview

 Classes: #wxFileHistory, #wxDocManager

 wxFileHistory encapsulates functionality to record the last few files visited, and
 to allow the user to quickly load these files using the list appended to the File menu.
 Although wxFileHistory is used by wxDocManager, it can be used independently. You may wish
 to derive from it to allow different behaviour, such as popping up a scrolling
 list of files.

 By calling wxFileHistory::UseMenu() you can associate a file menu with the file history. 
 The menu will then be used for appending filenames that are added to the history.

 Please notice that currently if the history already contained filenames when UseMenu() 
 is called (e.g. when initializing a second MDI child frame), the menu is not automatically
 initialized with the existing filenames in the history and so you need to call
 #AddFilesToMenu() after UseMenu() explicitly in order to initialize the menu with 
 the existing list of MRU files (otherwise an assertion failure is raised in debug builds).

 The filenames are appended using menu identifiers in the range @c wxID_FILE1 to @c wxID_FILE9.

 In order to respond to a file load command from one of these identifiers,
 you need to handle them using an event handler, for example:

 @code
 BEGIN_EVENT_TABLE(wxDocParentFrame, wxFrame)
     EVT_MENU(wxID_EXIT, wxDocParentFrame::OnExit)
     EVT_MENU_RANGE(wxID_FILE1, wxID_FILE9, wxDocParentFrame::OnMRUFile)
 END_EVENT_TABLE()

 void wxDocParentFrame::OnExit(wxCommandEvent& WXUNUSED(event))
 {
     Close();
 }

 void wxDocParentFrame::OnMRUFile(wxCommandEvent& event)
 {
       wxString f(m_docManager->GetHistoryFile(event.GetId() - wxID_FILE1));
       if (!f.empty())
         (void)m_docManager-CreateDocument(f, wxDOC_SILENT);
 }
 @endcode



 @section overview_docview_predefid wxWidgets predefined command identifiers

 To allow communication between the application's menus and the
 document/view framework, several command identifiers are predefined for you
 to use in menus.

 @verbatim
  wxID_OPEN (5000)
  wxID_CLOSE (5001)
  wxID_NEW (5002)
  wxID_SAVE (5003)
  wxID_SAVEAS (5004)
  wxID_REVERT (5005)
  wxID_EXIT (5006)
  wxID_UNDO (5007)
  wxID_REDO (5008)
  wxID_HELP (5009)
  wxID_PRINT (5010)
  wxID_PRINT_SETUP (5011)
  wxID_PREVIEW (5012)
 @endverbatim

*/