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