<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/extensions/motif/doc/walkthrough.doc:921 --> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>Refactoring Existing Code</title> <style type="text/css"><!-- fn { margin-left: 1cm; text-indent: -1cm; } a:link { color: #004faf; text-decoration: none } a:visited { color: #672967; text-decoration: none } body { background: #ffffff; color: black; } --></style> </head> <body> <table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr bgcolor="#E5E5E5"> <td valign=center> <a href="index.html"> <font color="#004faf">Home</font></a> | <a href="classes.html"> <font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"> <font color="#004faf">Main Classes</font></a> | <a href="annotated.html"> <font color="#004faf">Annotated</font></a> | <a href="groups.html"> <font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"> <font color="#004faf">Functions</font></a> </td> <td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Refactoring Existing Code</h1> [ <a href="motif-walkthrough-6.html">Previous: Using Qt Main Window Classes</a> ] [ <a href="motif-walkthrough.html">Home</a> ] [ <a href="motif-walkthrough-8.html">Next: Replacing the View Widget</a> ] <p> In the author's view, the existing code is slightly disorganized. Even though the code <em>does</em> work, some cleanups and reorganization can only help with readability and maintainability. The steps described below are not necessary during the migration process but are included for completeness. <p> <h2> Migrating Data Structures to C++ </h2> <a name="1"></a><p> The <tt>Page</tt> data structure is an opaque data type. The real data structure is called <tt>PageRec</tt>; <tt>Page</tt> defined to be a pointer to a <tt>PageRec</tt>. In addition, we have the <tt>AllocPage()</tt> function that allocates and initializes memory for a <tt>PageRec</tt> struct. <p> With C++, we can do this in the constructor. We can also write a destructor which automatically frees all resources in the <tt>PageRec</tt>, instead of having to do it in several different places. <p> The <tt>PageRec</tt> struct declaration is removed from <tt>page.h</tt>. We declare a <tt>Page</tt> struct with the same data members as <tt>PageRec</tt>, a constructor and a destructor. <p> <pre></pre> <p> The existing <tt>pages</tt>, <tt>currentPage</tt> and <tt>maxpages</tt> global variables are removed from the source files. We replace them with <tt>extern</tt> declarations in <tt>page.h</tt>. <p> <pre></pre> <p> The global variable instantiations are placed in <tt>todo.cpp</tt>. <p> Each source file contains function declarations that deal with the global <tt>Page</tt> related variables. We remove these declarations from the source files and declare them once in the <tt>page.h</tt> header file. <p> <pre></pre> <p> Now that <tt>Page</tt> has a constructor, we remove the <tt>AllocPage()</tt> function. It is no longer needed. The calls to <tt>AllocPage()</tt> are replaced with <tt>'new Page()'</tt> in the <tt>NewPage()</tt>, <tt>DeletePage()</tt> and <tt>ReadDB()</tt> functions. We also replace the code to deallocate pages with <tt>delete pages[X]</tt>, where <em>X</em> is the appropriate index value. This is done in the <tt>ReadDB</tt> and <tt>DeletePage()</tt> functions. <p> Code that accesses the global <tt>pages</tt> variable does not need to be modified since the data members of the <tt>Page</tt> struct did not change. The existing code will continue to work. <p> The <tt>OptionsRec</tt> struct declared in <tt>page.h</tt> is also updated, following the same pattern as the <tt>Page</tt> struct above. <p> <pre></pre> <p> The global variable instantiation is also placed in <tt>todo.cpp</tt>. <p> Code that accesses the global <tt>options</tt> variable does not need to be modified since the data members of the <tt>Options</tt> struct did not change. The existing code will continue to work. <p> <h2> Using <em>new</em> and <em>delete</em> </h2> <a name="2"></a><p> The destructors of the <tt>Page</tt> and <tt>Options</tt> structs use <em>delete</em> instead of <tt>XtFree()</tt> to deallocate all <tt>char*</tt> members. This is a necessary change since we are migrating away from Xt/Motif. We need to fix existing code that modifies the <tt>Page</tt> struct members to use <em>new</em> and <em>delete</em> ( instead of <tt>XtMalloc()</tt>, <tt>XtNewString()</tt> and <tt>XtFree()</tt> ). <p> The <tt>PageChange()</tt> function in <tt>todo.cpp</tt> simply saves the contents and cursor position of current page before calling <tt>SetPage()</tt>. We use <em>new</em> and <em>delete</em> when modifying members of the <tt>Page</tt> struct. <p> <pre></pre> <p> When storing the context of the <tt>XmText</tt> widget, we use <a href="qcstring.html#qstrdup">qstrdup</a>() to make a copy of the string returned by the <tt>XmTextGetString()</tt> function. <p> <pre></pre> <p> The <tt>ReadDB()</tt> function in <tt>io.cpp</tt> needs similar changes. We replace all use of <tt>XtMalloc()</tt> and <tt>XtNewString()</tt> with <em>new</em> and <a href="qcstring.html#qstrdup">qstrdup</a>(), respectively. <p> This needs to be done just after opening the file. <p> <pre></pre> <p> ... when starting a new page ... <p> <pre> ... </pre> <pre></pre> <p> ... and when reading in the label and tab texts/ <p> <pre> ... </pre> <pre></pre><pre> ... </pre> <pre></pre><pre> ... </pre> <pre></pre> <p> The <tt>ReadDB()</tt> function uses <tt>XtRealloc()</tt> to expand the data storage buffer. Unfortunately, C++ does not provide a way to reallocate an existing block of data, so we have to do this ourselves. <p> <pre></pre> <p> There is also one occurence in <tt>ReadDB()</tt> where we call <tt>XtMalloc()</tt> with an argument of 2. This was done when a file could not be read. Creating an empty string is not necessary, so we remove this code instead of using <em>new</em>. <p> <pre></pre> <p> The <tt>SaveDB()</tt> function in <tt>io.cpp</tt> also needs these changes. We change one occurence of <tt>XtFree()</tt> to <em>delete</em>. <p> <pre></pre> <p> Finally, We need to replace two occurences of <tt>XtNewString()</tt> in the <tt>main()</tt> function in <tt>todo.cpp</tt>. <p> <pre></pre> <p> <h2> Moving Existing Code </h2> <a name="3"></a><p> The rest of the refactoring process involves moving existing code into new places. Currently, each function in the <tt>mainwindow.ui.h</tt> file simply calls the old callback handlers present in the other files. Instead of calling the old callback functions, the implementations are moved accordingly. <p> <center><table cellpadding="4" cellspacing="2" border="0"> <tr bgcolor="#a2c511"> <th valign="top">Function <th valign="top">Original File <th valign="top">Moved to Function <tr bgcolor="#f0f0f0"> <td valign="top"><tt>New()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileNew()</tt> <tr bgcolor="#d0d0d0"> <td valign="top"><tt>Open()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileOpen()</tt> <tr bgcolor="#f0f0f0"> <td valign="top"><tt>SaveIt()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::fileSave()</tt> <tr bgcolor="#d0d0d0"> <td valign="top"><tt>Save()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileSaveAs()</tt> <tr bgcolor="#f0f0f0"> <td valign="top"><tt>ShowPrintDialog()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::filePrint()</tt> <tr bgcolor="#d0d0d0"> <td valign="top"><tt>EditPage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selProperties()</tt> <tr bgcolor="#f0f0f0"> <td valign="top"><tt>NewPage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selNewPage()</tt> <tr bgcolor="#d0d0d0"> <td valign="top"><tt>DeletePage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selDeletePage()</tt> </table></center> <p> The <tt>Print()</tt> callback function is still used by the <em>Print</em> dialog, so we move it into <tt>mainwindow.ui.h</tt> and make it <tt>static</tt>. <p> Previously, the <tt>Open()</tt>, <tt>Save()</tt>, <tt>EditPage()</tt> and <tt>DeletePage()</tt> functions created dialogs with <em>client_data</em> as the parent argument. Since we have moved the code directly into the <em>Main Window</em> implementation, we create these dialogs with <em>this</em> as the parent argument. <p> The <tt>PageChange()</tt> callback function is moved from <tt>actions.cpp</tt> to <tt>todo.cpp</tt> and made <tt>static</tt> since it is not used anywhere else. <p> Earlier modifications to <tt>actions.cpp</tt> caused the <tt>Trim()</tt> function to become redundant, so we remove it. <p> The <tt>MIN()</tt> and <tt>MAX()</tt> macros in <tt>todo.cpp</tt> are redundant. Qt provides the <tt>QMIN()</tt> and <tt>QMAX()</tt> macros which we will use. <p> Earlier modifications caused the <tt>fallback_resources</tt> array to become redundant, so we remove it. <p> In the near future, our program will not use <a href="motif-extension.html#Motif">Motif</a> any more, and we will no longer need to use <a href="qmotif.html">QMotif</a>. To prepare for this, we remove the <tt>resources</tt> and <tt>optionDesc</tt> arrays and create the QMotif instance with just the <em>APP_CLASS</em> argument. <p> The <tt>#include</tt> statements in the source files are mostly incorrect due to the refactoring changes. Many of the <tt>#include</tt> statements are no longer needed. The <tt>#include</tt> statements from each file are listed below, instead of describing which includes are removed and added to each file. <p> Includes for <tt>actions.cpp</tt>: <p> <pre></pre> <p> Includes for <tt>io.cpp</tt>: <p> <pre></pre><pre></pre><pre></pre> <p> Includes for <tt>todo.cpp</tt>: <p> <pre></pre><pre></pre><pre></pre> <p> Includes for <tt>mainwindow.ui.h</tt>: <p> <pre></pre><pre></pre><pre></pre><pre></pre><pre></pre> <p> [ <a href="motif-walkthrough-6.html">Previous: Using Qt Main Window Classes</a> ] [ <a href="motif-walkthrough.html">Home</a> ] [ <a href="motif-walkthrough-8.html">Next: Replacing the View Widget</a> ] <p> <!-- eof --> <p><address><hr><div align=center> <table width=100% cellspacing=0 border=0><tr> <td>Copyright © 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>