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| 32 | <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>
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| 33 |
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| 34 |
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| 35 |
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| 36 | [ <a href="motif-walkthrough-6.html">Previous: Using Qt Main Window Classes</a> ]
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| 37 | [ <a href="motif-walkthrough.html">Home</a> ]
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| 38 | [ <a href="motif-walkthrough-8.html">Next: Replacing the View Widget</a> ]
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| 39 | <p> In the author's view, the existing code is slightly disorganized.
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| 40 | Even though the code <em>does</em> work, some cleanups and reorganization
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| 41 | can only help with readability and maintainability. The steps
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| 42 | described below are not necessary during the migration process but are
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| 43 | included for completeness.
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| 44 | <p> <h2> Migrating Data Structures to C++
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| 45 | </h2>
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| 46 | <a name="1"></a><p> The <tt>Page</tt> data structure is an opaque data type. The real data
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| 47 | structure is called <tt>PageRec</tt>; <tt>Page</tt> defined to be a pointer to a
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| 48 | <tt>PageRec</tt>. In addition, we have the <tt>AllocPage()</tt> function that
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| 49 | allocates and initializes memory for a <tt>PageRec</tt> struct.
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| 50 | <p> With C++, we can do this in the constructor. We can also write a
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| 51 | destructor which automatically frees all resources in the <tt>PageRec</tt>,
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| 52 | instead of having to do it in several different places.
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| 53 | <p> The <tt>PageRec</tt> struct declaration is removed from <tt>page.h</tt>. We
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| 54 | declare a <tt>Page</tt> struct with the same data members as <tt>PageRec</tt>, a
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| 55 | constructor and a destructor.
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| 56 | <p>
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| 57 |
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| 58 | <pre></pre>
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| 59 | <p> The existing <tt>pages</tt>, <tt>currentPage</tt> and <tt>maxpages</tt> global variables
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| 60 | are removed from the source files. We replace them with <tt>extern</tt>
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| 61 | declarations in <tt>page.h</tt>.
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| 62 | <p> <pre></pre>
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| 63 | <p> The global variable instantiations are placed in <tt>todo.cpp</tt>.
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| 64 | <p> Each source file contains function declarations that deal with the
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| 65 | global <tt>Page</tt> related variables. We remove these declarations from
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| 66 | the source files and declare them once in the <tt>page.h</tt> header file.
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| 67 | <p> <pre></pre>
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| 68 | <p> Now that <tt>Page</tt> has a constructor, we remove the <tt>AllocPage()</tt>
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| 69 | function. It is no longer needed. The calls to <tt>AllocPage()</tt> are
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| 70 | replaced with <tt>'new Page()'</tt> in the <tt>NewPage()</tt>, <tt>DeletePage()</tt>
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| 71 | and <tt>ReadDB()</tt> functions. We also replace the code to deallocate
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| 72 | pages with <tt>delete pages[X]</tt>, where <em>X</em> is the appropriate index
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| 73 | value. This is done in the <tt>ReadDB</tt> and <tt>DeletePage()</tt> functions.
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| 74 | <p> Code that accesses the global <tt>pages</tt> variable does not need to be
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| 75 | modified since the data members of the <tt>Page</tt> struct did not change.
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| 76 | The existing code will continue to work.
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| 77 | <p> The <tt>OptionsRec</tt> struct declared in <tt>page.h</tt> is also updated,
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| 78 | following the same pattern as the <tt>Page</tt> struct above.
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| 79 | <p> <pre></pre>
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| 80 | <p> The global variable instantiation is also placed in <tt>todo.cpp</tt>.
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| 81 | <p> Code that accesses the global <tt>options</tt> variable does not need to be
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| 82 | modified since the data members of the <tt>Options</tt> struct did not
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| 83 | change. The existing code will continue to work.
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| 84 | <p> <h2> Using <em>new</em> and <em>delete</em>
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| 85 | </h2>
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| 86 | <a name="2"></a><p> The destructors of the <tt>Page</tt> and <tt>Options</tt> structs use <em>delete</em>
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| 87 | instead of <tt>XtFree()</tt> to deallocate all <tt>char*</tt> members. This is a
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| 88 | necessary change since we are migrating away from Xt/Motif. We need
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| 89 | to fix existing code that modifies the <tt>Page</tt> struct members to use
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| 90 | <em>new</em> and <em>delete</em> ( instead of <tt>XtMalloc()</tt>, <tt>XtNewString()</tt> and
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| 91 | <tt>XtFree()</tt> ).
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| 92 | <p> The <tt>PageChange()</tt> function in <tt>todo.cpp</tt> simply saves the contents
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| 93 | and cursor position of current page before calling <tt>SetPage()</tt>. We
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| 94 | use <em>new</em> and <em>delete</em> when modifying members of the <tt>Page</tt> struct.
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| 95 | <p>
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| 96 |
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| 97 | <pre></pre>
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| 98 | <p> When storing the context of the <tt>XmText</tt> widget, we use <a href="qcstring.html#qstrdup">qstrdup</a>()
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| 99 | to make a copy of the string returned by the <tt>XmTextGetString()</tt>
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| 100 | function.
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| 101 | <p> <pre></pre>
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| 102 | <p> The <tt>ReadDB()</tt> function in <tt>io.cpp</tt> needs similar changes. We
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| 103 | replace all use of <tt>XtMalloc()</tt> and <tt>XtNewString()</tt> with <em>new</em> and
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| 104 | <a href="qcstring.html#qstrdup">qstrdup</a>(), respectively.
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| 105 | <p> This needs to be done just after opening the file.
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| 106 | <p>
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| 107 |
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| 108 | <pre></pre>
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| 109 | <p> ... when starting a new page ...
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| 110 | <p> <pre>
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| 111 | ...
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| 112 | </pre>
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| 113 |
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| 114 | <pre></pre>
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| 115 | <p> ... and when reading in the label and tab texts/
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| 116 | <p> <pre>
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| 117 | ...
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| 118 | </pre>
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| 119 |
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| 120 | <pre></pre><pre>
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| 121 | ...
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| 122 | </pre>
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| 123 |
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| 124 | <pre></pre><pre>
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| 125 | ...
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| 126 | </pre>
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| 127 |
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| 128 | <pre></pre>
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| 129 | <p> The <tt>ReadDB()</tt> function uses <tt>XtRealloc()</tt> to expand the data
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| 130 | storage buffer. Unfortunately, C++ does not provide a way to
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| 131 | reallocate an existing block of data, so we have to do this ourselves.
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| 132 | <p> <pre></pre>
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| 133 | <p> There is also one occurence in <tt>ReadDB()</tt> where we call <tt>XtMalloc()</tt>
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| 134 | with an argument of 2. This was done when a file could not be read.
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| 135 | Creating an empty string is not necessary, so we remove this code
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| 136 | instead of using <em>new</em>.
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| 137 | <p> <pre></pre>
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| 138 | <p> The <tt>SaveDB()</tt> function in <tt>io.cpp</tt> also needs these changes. We
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| 139 | change one occurence of <tt>XtFree()</tt> to <em>delete</em>.
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| 140 | <p> <pre></pre>
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| 141 | <p> Finally, We need to replace two occurences of <tt>XtNewString()</tt> in the <tt>main()</tt> function in <tt>todo.cpp</tt>.
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| 142 | <p>
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| 143 |
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| 144 | <pre></pre>
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| 145 | <p> <h2> Moving Existing Code
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| 146 | </h2>
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| 147 | <a name="3"></a><p> The rest of the refactoring process involves moving existing code into
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| 148 | new places. Currently, each function in the <tt>mainwindow.ui.h</tt> file
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| 149 | simply calls the old callback handlers present in the other files.
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| 150 | Instead of calling the old callback functions, the implementations are
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| 151 | moved accordingly.
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| 152 | <p> <center><table cellpadding="4" cellspacing="2" border="0">
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| 153 | <tr bgcolor="#a2c511"> <th valign="top">Function <th valign="top">Original File <th valign="top">Moved to Function
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| 154 | <tr bgcolor="#f0f0f0"> <td valign="top"><tt>New()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileNew()</tt>
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| 155 | <tr bgcolor="#d0d0d0"> <td valign="top"><tt>Open()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileOpen()</tt>
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| 156 | <tr bgcolor="#f0f0f0"> <td valign="top"><tt>SaveIt()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::fileSave()</tt>
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| 157 | <tr bgcolor="#d0d0d0"> <td valign="top"><tt>Save()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::fileSaveAs()</tt>
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| 158 | <tr bgcolor="#f0f0f0"> <td valign="top"><tt>ShowPrintDialog()</tt> <td valign="top"><tt>todo.cpp</tt> <td valign="top"><tt>MainWindow::filePrint()</tt>
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| 159 | <tr bgcolor="#d0d0d0"> <td valign="top"><tt>EditPage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selProperties()</tt>
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| 160 | <tr bgcolor="#f0f0f0"> <td valign="top"><tt>NewPage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selNewPage()</tt>
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| 161 | <tr bgcolor="#d0d0d0"> <td valign="top"><tt>DeletePage()</tt> <td valign="top"><tt>actions.cpp</tt> <td valign="top"><tt>MainWindow::selDeletePage()</tt>
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| 162 | </table></center>
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| 163 | <p> The <tt>Print()</tt> callback function is still used by the <em>Print</em>
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| 164 | dialog, so we move it into <tt>mainwindow.ui.h</tt> and make it <tt>static</tt>.
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| 165 | <p> Previously, the <tt>Open()</tt>, <tt>Save()</tt>, <tt>EditPage()</tt> and <tt>DeletePage()</tt>
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| 166 | functions created dialogs with <em>client_data</em> as the parent argument.
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| 167 | Since we have moved the code directly into the <em>Main Window</em>
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| 168 | implementation, we create these dialogs with <em>this</em> as the parent
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| 169 | argument.
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| 170 | <p> The <tt>PageChange()</tt> callback function is moved from <tt>actions.cpp</tt>
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| 171 | to <tt>todo.cpp</tt> and made <tt>static</tt> since it is not used anywhere else.
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| 172 | <p> Earlier modifications to <tt>actions.cpp</tt> caused the <tt>Trim()</tt> function
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| 173 | to become redundant, so we remove it.
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| 174 | <p> The <tt>MIN()</tt> and <tt>MAX()</tt> macros in <tt>todo.cpp</tt> are redundant. Qt
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| 175 | provides the <tt>QMIN()</tt> and <tt>QMAX()</tt> macros which we will use.
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| 176 | <p> Earlier modifications caused the <tt>fallback_resources</tt> array to become
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| 177 | redundant, so we remove it.
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| 178 | <p> In the near future, our program will not use <a href="motif-extension.html#Motif">Motif</a> any more, and we
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| 179 | will no longer need to use <a href="qmotif.html">QMotif</a>. To prepare for this, we remove the
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| 180 | <tt>resources</tt> and <tt>optionDesc</tt> arrays and create the QMotif instance
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| 181 | with just the <em>APP_CLASS</em> argument.
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| 182 | <p> The <tt>#include</tt> statements in the source files are mostly incorrect
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| 183 | due to the refactoring changes. Many of the <tt>#include</tt> statements
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| 184 | are no longer needed. The <tt>#include</tt> statements from each file are
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| 185 | listed below, instead of describing which includes are removed and
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| 186 | added to each file.
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| 187 | <p> Includes for <tt>actions.cpp</tt>:
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| 188 | <p>
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| 189 |
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| 190 | <pre></pre>
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| 191 | <p> Includes for <tt>io.cpp</tt>:
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| 192 | <p>
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| 193 |
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| 194 | <pre></pre><pre></pre><pre></pre>
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| 195 | <p> Includes for <tt>todo.cpp</tt>:
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| 196 | <p>
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| 197 |
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| 198 | <pre></pre><pre></pre><pre></pre>
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| 199 | <p> Includes for <tt>mainwindow.ui.h</tt>:
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| 200 | <p>
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| 201 |
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| 202 | <pre></pre><pre></pre><pre></pre><pre></pre><pre></pre>
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| 203 | <p> [ <a href="motif-walkthrough-6.html">Previous: Using Qt Main Window Classes</a> ]
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| 204 | [ <a href="motif-walkthrough.html">Home</a> ]
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| 205 | [ <a href="motif-walkthrough-8.html">Next: Replacing the View Widget</a> ]
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| 206 | <p>
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| 207 | <!-- eof -->
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| 208 | <p><address><hr><div align=center>
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| 210 | <td>Copyright © 2007
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| 211 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 212 | <td align=right><div align=right>Qt 3.3.8</div>
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| 213 | </table></div></address></body>
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