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Errors can be corrected by clicking the Undo button. Once the letter has been prepared it can be printed or saved as HTML. \section1 MainWindow Class Definition Here's the class definition: \snippet examples/mainwindows/dockwidgets/mainwindow.h 0 We will now review each function in turn. \section1 MainWindow Class Implementation \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 0 We start by including \c , a header file that contains the definition of all classes in the \l QtCore and \l QtGui libraries. This saves us from having to include every class individually and is especially convenient if we add new widgets. We also include \c mainwindow.h. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 1 In the constructor, we start by creating a QTextEdit widget. Then we call QMainWindow::setCentralWidget(). This function passes ownership of the QTextEdit to the \c MainWindow and tells the \c MainWindow that the QTextEdit will occupy the \c MainWindow's central area. Then we call \c createActions(), \c createMenus(), \c createToolBars(), \c createStatusBar(), and \c createDockWindows() to set up the user interface. Finally we call \c setWindowTitle() to give the application a title, and \c newLetter() to create a new letter template. We won't quote the \c createActions(), \c createMenus(), \c createToolBars(), and \c createStatusBar() functions since they follow the same pattern as all the other Qt examples. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 9 We create the customers dock window first, and in addition to a window title, we also pass it a \c this pointer so that it becomes a child of \c MainWindow. Normally we don't have to pass a parent because widgets are parented automatically when they are laid out: but dock windows aren't laid out using layouts. We've chosen to restrict the customers dock window to the left and right dock areas. (So the user cannot drag the dock window to the top or bottom dock areas.) The user can drag the dock window out of the dock areas entirely so that it becomes a free floating window. We can change this (and whether the dock window is moveable or closable) using QDockWidget::setFeatures(). Once we've created the dock window we create a list widget with the dock window as parent, then we populate the list and make it the dock window's widget. Finally we add the dock widget to the \c MainWindow using \c addDockWidget(), choosing to put it in the right dock area. We undertake a similar process for the paragraphs dock window, except that we don't restrict which dock areas it can be dragged to. Finally we set up the signal-slot connections. If the user clicks a customer or a paragraph their \c currentTextChanged() signal will be emitted and we connect these to \c insertCustomer() and addParagraph() passing the text that was clicked. We briefly discuss the rest of the implementation, but have now covered everything relating to dock windows. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 2 In this function we clear the QTextEdit so that it is empty. Next we create a QTextCursor on the QTextEdit. We move the cursor to the start of the document and create and format a frame. We then create some character formats and a table format. We insert a table into the document and insert the company's name and address into a table using the table and character formats we created earlier. Then we insert the skeleton of the letter including two markers \c NAME and \c ADDRESS. We will also use the \c{Yours sincerely,} text as a marker. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 6 If the user clicks a customer we split the customer details into pieces. We then look for the \c NAME marker using the \c find() function. This function selects the text it finds, so when we call \c insertText() with the customer's name the name replaces the marker. We then look for the \c ADDRESS marker and replace it with each line of the customer's address. Notice that we wrapped all the insertions between a \c beginEditBlock() and \c endEditBlock() pair. This means that the entire name and address insertion is treated as a single operation by the QTextEdit, so a single undo will revert all the insertions. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 7 This function works in a similar way to \c insertCustomer(). First we look for the marker, in this case, \c {Yours sincerely,}, and then replace it with the standard paragraph that the user clicked. Again we use a \c beginEditBlock() ... \c endEditBlock() pair so that the insertion can be undone as a single operation. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 3 Qt's QTextDocument class makes printing documents easy. We simply take the QTextEdit's QTextDocument, set up the printer and print the document. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 4 QTextEdit can output its contents in HTML format, so we prompt the user for the name of an HTML file and if they provide one we simply write the QTextEdit's contents in HTML format to the file. \snippet examples/mainwindows/dockwidgets/mainwindow.cpp 5 If the focus is in the QTextEdit, pressing \key Ctrl+Z undoes as expected. But for the user's convenience we provide an application-wide undo function that simply calls the QTextEdit's undo: this means that the user can undo regardless of where the focus is in the application. */