tdocview.tex

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%% Name:        tdocview.tex
%% Purpose:     Document/view overview
%% Author:      wxWidgets Team
%% Modified by:
%% Created:
%% RCS-ID:      $Id: tdocview.tex,v 1.12 2005/11/16 17:27:33 ABX Exp $
%% Copyright:   (c) wxWidgets Team
%% License:     wxWindows license
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\section{Document/view overview}\label{docviewoverview}

Classes: \helpref{wxDocument}{wxdocument}, \helpref{wxView}{wxview}, \helpref{wxDocTemplate}{wxdoctemplate},\rtfsp
\helpref{wxDocManager}{wxdocmanager}, \helpref{wxDocParentFrame}{wxdocparentframe}, \helpref{wxDocChildFrame}{wxdocchildframe},
\rtfsp\helpref{wxDocMDIParentFrame}{wxdocmdiparentframe}, \helpref{wxDocMDIChildFrame}{wxdocmdichildframe},
\rtfsp\helpref{wxCommand}{wxcommand}, \helpref{wxCommandProcessor}{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 {\it documents} to store data
and provide interface-independent operations upon it, and {\it 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:

\begin{enumerate}\itemsep=0pt
\item Define your own document and view classes, overriding a minimal set of
member functions e.g. for input/output, drawing and initialization.
\item 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.
\item 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).
\item 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).
\item 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.
\end{enumerate}

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:

\begin{itemize}\itemsep=0pt
\item Override wxDocument::OnCreateCommandProcessor to define a different Do/Undo strategy,
or a command history editor.
\item Override wxView::OnCreatePrintout to create an instance of a derived \helpref{wxPrintout}{wxprintout}\rtfsp
class, to provide multi-page document facilities.
\item Override wxDocManager::SelectDocumentPath to provide a different file selector.
\item Limit the maximum number of open documents and the maximum number of undo commands.
\end{itemize}

Note that to activate framework functionality, you need to use some or all of
the wxWidgets \helpref{predefined command identifiers}{predefinedids} in your menus.

\perlnote{The document/view framework is available in wxPerl. To use it,
you will need the following statements in your application code:\par
{\small
\begin{verbatim}
use Wx::DocView;
use Wx ':docview';   # import constants (optional)
\end{verbatim}
}}

\subsection{wxDocument overview}\label{wxdocumentoverview}

\overview{Document/view framework overview}{docviewoverview}

Class: \helpref{wxDocument}{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 \helpref{wxView}{wxview}, \helpref{wxDocTemplate}{wxdoctemplate}\rtfsp
and \helpref{wxDocManager}{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 {\it 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 {\it views} on {\it documents} or the ability to open, edit and save
files. But probably the majority of applications are document-based.

See the example application in {\tt 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 \helpref{wxDocTemplate}{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.

\subsection{wxView overview}\label{wxviewoverview}

\overview{Document/view framework overview}{docviewoverview}

Class: \helpref{wxView}{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 \helpref{wxDocument}{wxdocument}, \helpref{wxDocTemplate}{wxdoctemplate}
and \helpref{wxDocManager}{wxdocmanager} classes.

See the example application in {\tt 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 \helpref{wxDocTemplate}{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.

\subsection{wxDocTemplate overview}\label{wxdoctemplateoverview}

\overview{Document/view framework overview}{docviewoverview}

Class: \helpref{wxDocTemplate}{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.