Add Qt3 development HEAD version

author: Timothy Pearson <kb9vqf@pearsoncomputing.net> 2011-07-10 15:24:15 -0500
committer: Timothy Pearson <kb9vqf@pearsoncomputing.net> 2011-07-10 15:24:15 -0500
commit: bd0f3345a938b35ce6a12f6150373b0955b8dd12 (patch)
tree: 7a520322212d48ebcb9fbe1087e7fca28b76185c /doc/html/motif-walkthrough-8.html
download: qt3-bd0f3345a938b35ce6a12f6150373b0955b8dd12.tar.gz
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+<title>Replacing the View Widget</title>
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+<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Replacing the View Widget</h1>
+
+
+
+[ <a href="motif-walkthrough-7.html">Previous: Refactoring Existing Code</a> ]
+[ <a href="motif-walkthrough.html">Home</a> ]
+[ <a href="motif-walkthrough-9.html">Next: Replacing the Print Dialog</a> ]
+<p> We are ready to start replacing the <em>View</em> widget.  However, our
+example program uses the <tt>XmNotebook</tt> widget class.  Qt does not
+provide a direct equivalent of this class, so we are faced with three
+possibilities, each with several advantages and disadvantages.
+<p> <ol type=1>
+<p> <li> We can continue the conversion using existing Qt widgets.
+<p> <ul>
+<p> <li> Advantages - The widgets provided by Qt are well designed and
+tested, allowing us to quickly redesign the user interface.
+<p> <li> Disadvantages - Most, if not all, of the existing data structures
+and code will need to be modified or rewritten.  New code must be
+written in a way that maintains compatibility with previous versions
+of our application.
+<p> </ul>
+<p> <li> We can write a new <a href="qwidget.html">QWidget</a> subclass that is identical to the <tt>XmNotebook</tt> widget class.
+<p> <ul>
+<p> <li> Advantages - The existing data structures will not change, allowing
+compatibility with previous and future versions.
+<p> <li> Disadvantages - The new widget will need to be written and
+regression tested.  Existing code in our application will need to be
+changed in order to deal with the new widget's API.
+<p> </ul>
+<p> <li> We can leave the <tt>XmNotebook</tt> widget untouched.
+<p> <ul>
+<p> <li> Advantages - The existing data structures and code remain
+unchanged, allowing us to continue development on other projects,
+new features, etc.
+<p> <li> Disadvantages - This is the simplest solution, but the application
+will still be dependent upon X11; we will not be able to deploy our
+application on all platforms supported by Qt.
+<p> </ul>
+<p> </ol>
+<p> We will use the first approach to complete the migration of the
+example project used in this walkthrough, using <a href="qtextedit.html">QTextEdit</a>, <a href="qlabel.html">QLabel</a> and
+<a href="qspinbox.html">QSpinBox</a> to provide a similar look.  The only difference is that we
+will not have tabs.
+<p> We use <a href="designer-manual.html">Qt Designer</a> to add the
+QTextEdit, QLabel and QSpinBox widgets to the <em>Main Window</em> widget.
+<p> <h2> Data Structure Modifications
+</h2>
+<a name="1"></a><p> The <tt>Page</tt> struct contains <tt>majorPB</tt> and <tt>minorPB</tt> members which
+need to be removed.  These members correspond to the tabs displayed in
+the existing version.  The new version will not have any tabs, so we
+remove them.
+<p> 
+
+<pre></pre>
+<p> <h2> Code Modifications
+</h2>
+<a name="2"></a><p> Most of the existing functions in our application need to be modified
+to work with the new <em>View</em> widget.  The <tt>MainWindow</tt> class has five
+new functions that correspond to existing functions.
+<p> <center><table cellpadding="4" cellspacing="2" border="0">
+<tr bgcolor="#a2c511"> <th valign="top">Existing Function            <th valign="top">New Function 
+<tr bgcolor="#f0f0f0">    <td valign="top"><tt>void SetPage( int )</tt>    <td valign="top"><tt>void MainWindow::setPage( int )</tt>
+<tr bgcolor="#d0d0d0">    <td valign="top"><tt>void PageChange( ... )</tt>  <td valign="top"><tt>void MainWnidow::pageChange( int )</tt>
+<tr bgcolor="#f0f0f0">    <td valign="top"><tt>void TextChanged( ... )</tt> <td valign="top"><tt>void MainWnidow::textChanged()</tt>
+<tr bgcolor="#d0d0d0">    <td valign="top"><tt>void ReadDB( char * )</tt>   <td valign="top"><tt>void MainWindow::readDB( char * )</tt>
+<tr bgcolor="#f0f0f0">    <td valign="top"><tt>void SaveDB( char * )</tt>   <td valign="top"><tt>void MainWindow::saveDB( char * )</tt>
+</table></center>
+<p> <a name="mainwindow-ui-h-view-widget-modifications"></a>
+<p> The <tt>SetPage()</tt> function implementation is moved to the <tt>MainWindow::setPage()</tt> function in <tt>mainwindow.ui.h</tt>.  We remove the
+<tt>SetPage()</tt> function declaration and implementation from <tt>page.h</tt>
+and <tt>actions.cpp</tt>, respectively.  In order to make <tt>MainWindow::setPage()</tt> work correctly, we need to modify the code to
+use the new widgets in our <em>Main Window</em> widget.
+<p> 
+
+<pre></pre>
+<p> First, we set the current value of the <tt>spinbox</tt> to the current page
+number.
+<p> <pre></pre>
+<p> Next, we set the current text and cursor position of the <tt>textedit</tt>
+to the contents of the current page.
+<p> <pre></pre>
+<p> If the current page has a custom label, we set it as the current text
+of the <tt>textlabel</tt>; otherwise we set the <tt>textlabel</tt> contents to
+"Page X" (where X is the current page number).
+<p> <pre></pre>
+<p> If the current page has major and/or minor tab text, we append these
+to the <tt>labeltext</tt>.  This ensures that all information entered by the
+user remains visible.
+<p> <pre></pre>
+<p> We should continue to handle the possibility that the current page
+does not exist.  In this case, we clear the contents of the <tt>textedit</tt> widget and set the <tt>textlabel</tt> contents to the current page
+number (with an indication that the page is invalid).
+<p> <pre></pre>
+<p> The <tt>PageChange()</tt> function is moved from <tt>todo.cpp</tt> to the <tt>MainWindow::pageChange()</tt> function in <tt>mainwindow.ui.h</tt>.  As with the
+<tt>MainWindow::setPae()</tt> function, we need to modify the code to use
+the new widgets in our <em>Main Window</em> widget.
+<p> Note: <a href="qtextedit.html#text">QTextEdit::text</a>() returns a <a href="qstring.html">QString</a>, which needs to be converted
+into a normal <tt>char*</tt> array.  To do this we create a copy of the
+string in the local encoding.  We need to make the copy using <a href="qcstring.html#qstrdup">qstrdup</a>() because the data contained in the <a href="qcstring.html">QCString</a> returned by
+<a href="qstring.html#local8Bit">QString::local8Bit</a>() is deallocated when the QCString is destroyed.
+<p> <pre></pre>
+<p> The <tt>TextChanged()</tt> function does nothing more than set the <tt>modified</tt> variable to 1.  Our new <tt>MainWindow::textChanged()</tt> function
+does exactly the same.
+<p> <pre></pre>
+<p> Since both the <tt>MainWindow::pageChange()</tt> and <tt>MainWindow::textChanged()</tt> functions access the <tt>modified</tt> global
+variable, we add a forward declaration at the top of <tt>mainwindow.ui.h</tt>.
+<p> <a name="io-cpp-view-widget-modifications"></a>
+<p> The <tt>ReadDB()</tt> and \s SaveDB() implementations in <tt>io.cpp</tt> are
+renamed to <tt>MainWindow::readDB()</tt> and <tt>MainWindow::saveDB()</tt>,
+respectively.  We need to modify the code in order to make the code
+work properly.
+<p> First, We add <tt>#include</tt> statements for the <tt>MainWindow</tt>, <a href="qspinbox.html">QSpinBox</a>
+and <a href="qtextedit.html">QTextEdit</a> classes.
+<p> 
+
+<pre></pre><pre></pre>
+<p> The new <tt>MainWindow::readDB()</tt> and <tt>MainWindow::saveDB()</tt> functions
+will not use any Xt/Motif functions, so we remove the Xt/Motif <tt>#include</tt> statements and the global variables <tt>notebook</tt> and <tt>textw</tt>.
+These functions remain largely unchanged, maintaining compatibility
+with previous versions.  Also, the <tt>ReadDB()</tt> and <tt>SaveDB()</tt>
+functions have been converted into <tt>MainWindow</tt> member functions, so
+we can pass <em>this</em> as the <em>parent</em> argument to the <a href="qmessagebox.html">QMessageBox</a>
+functions.
+<p> <pre></pre>
+<p> After reading the file in the <tt>MainWindow::readDB()</tt> function, we set
+the current and maximum values of the <tt>spinbox</tt> to the appropriate
+values.
+<p> 
+
+<p> <pre></pre>
+<p> In the <tt>MainWindow::saveDB()</tt> function, we need to store the text
+currently displayed, so we use <a href="qtextedit.html#text">QTextEdit::text</a>() instead of <tt>XmTextGetString()</tt>.  Note: QTextEdit::text() returns a <a href="qstring.html">QString</a>, which
+needs to be converted into a normal <tt>char*</tt> array.  To do this we
+create a copy of the string in the local encoding.  We need to make
+the copy using <a href="qcstring.html#qstrdup">qstrdup</a>() because the data contained in the <a href="qcstring.html">QCString</a>
+returned by <a href="qstring.html#local8Bit">QString::local8Bit</a>() is deallocated when the QCString is
+destroyed.
+<p> <pre></pre>
+<p> <a name="actions-cpp-viewwidget-modifications"></a>
+<p> Due to the removal of the <tt>majorPB</tt> and <tt>minorPB</tt> members from the
+<tt>Page</tt> struct, the <tt>FixPages()</tt> function in <tt>actions.cpp</tt> is no
+longer needed.  We remove the implementation and forward declaration
+of <tt>FixPages()</tt> from <tt>actions.cpp</tt> and <tt>page.h</tt>, respectively.
+Calls to <tt>FixPages()</tt> are removed from the <tt>MainWindow::selNewPage()</tt> and <tt>MainWindow::selDeletePage()</tt>, both of
+which are in <tt>mainwindow.ui.h</tt>.
+<p> We move <tt>AdjustPages()</tt> to <tt>mainwindow.ui.h</tt> and make it <tt>static</tt>,
+since it is only used in this file.  We remove the forward declaration
+from <tt>page.h</tt> as well.
+<p> After our modifications, the <tt>actions.cpp</tt> file is empty. We remove
+it from our project file and regenerate our <tt>Makefile</tt>.
+<p> <a name="todo-cpp-view-widget-modifications"></a>
+<p> Now that we have implemented our new <em>View</em> widget, we need to remove
+the old <a href="motif-extension.html#Motif">Motif</a> based view widget from <tt>todo.cpp</tt>.
+<p> Since we will not be using any Motif widgets, we remove all Motif <tt>#include</tt> statements, including <a href="qmotifwidget-h.html">qmotifwidget.h</a>. 
+<p> 
+
+<pre></pre><pre></pre>
+<p> We also remove the forward declarations of the <tt>ReadDB()</tt> function
+and the <tt>notebook</tt>, <tt>textw</tt> and <tt>labelw</tt> global variables.
+<p> <pre></pre>
+<p> Next, we remove the <tt>center</tt> widget, which uses <a href="qmotifwidget.html">QMotifWidget</a>.  The <em>Main Window</em> widget and <em>View</em> widget are contained entirely in our
+<tt>MainWindow</tt> class, so no extra initialization is needed after
+creating the <tt>mainwindow</tt> widget.
+<p> <pre></pre>
+<p> Since the <tt>ReadDB()</tt> and <tt>SetPage()</tt> functions have been changed into
+<tt>MainWindow</tt> member functions, we need to call them using our <tt>mainwindow</tt> instance.
+<p> <pre></pre>
+<p> The <em>View</em> widget has now been replaced.  After building our project,
+we confirm that the application works correctly.
+<p> [ <a href="motif-walkthrough-7.html">Previous: Refactoring Existing Code</a> ]
+[ <a href="motif-walkthrough.html">Home</a> ]
+[ <a href="motif-walkthrough-9.html">Next: Replacing the Print Dialog</a> ]
+<p> 
+<!-- eof -->
+<p><address><hr><div align=center>
+<table width=100% cellspacing=0 border=0><tr>
+<td>Copyright &copy; 2007
+<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
+<td align=right><div align=right>Qt 3.3.8</div>
+</table></div></address></body>
+</html>
author	Timothy Pearson <kb9vqf@pearsoncomputing.net>	2011-07-10 15:24:15 -0500
committer	Timothy Pearson <kb9vqf@pearsoncomputing.net>	2011-07-10 15:24:15 -0500
commit	bd0f3345a938b35ce6a12f6150373b0955b8dd12 (patch)
tree	7a520322212d48ebcb9fbe1087e7fca28b76185c /doc/html/motif-walkthrough-8.html
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