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<table border="0" cellspacing="0" cellpadding="3" width="100%"><tr><td> <div align="center" id="bldcontent"> <a href="../default.htm"><img src="../images/opendocs.png" width="63" height="76" border="0"></a> <br> <div class="symbol">Your OpenSource Publisher™</div> </div> </td></tr></table> <div align="center" class="author"> <a href="../products.lxp">Products</a> | <a href="../wheretobuy.lxp">Where to buy</a> | <a href="../bookstore.lxp">Retailers</a> | <a href="../faq.lxp">FAQ</a> | <a href="../writeforus.lxp">Write for Us.</a> | <a href="#contact">Contact Us.</a> </div> <table border="0" cellspacing="3" cellpadding="0" width="100%"><tr><td width="100%"> <div class="content"> <table border="0" cellspacing="2" cellpadding="0" width="100%"><tr><td width="100%"> <div align="center"><H4 CLASS="AUTHOR"><A NAME="AEN5">Boudewijn Rempt</A><br><a href="../../https@secure.linuxports.com/opendocs/default.htm"><img src=odpyqt125.png></a><br>ISBN: 0-97003300-4-4<br><a href="../../https@secure.linuxports.com/opendocs/default.htm">Available from bookstores everywhere or you can order it here.</a><p>You can download the source files for the book <a href="pyqtsrc.tgz">(code / eps) here.</a><hr></div> <HTML><HEAD><TITLE>The document</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.72"><LINKREL="HOME"TITLE="GUI Programming with Python: QT Edition"HREF="book1.htm"><LINKREL="UP"TITLE="Creating Application Functionality"HREF="c5783.htm"><LINKREL="PREVIOUS"TITLE="The view"HREF="x5798.htm"><LINKREL="NEXT"TITLE="Saving and loading documents"HREF="x5925.htm"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#0000FF"VLINK="#840084"ALINK="#0000FF"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">GUI Programming with Python: QT Edition</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><A accesskey="P" href="index.lxp@lxpwrap=x5798_252ehtm.htm">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 17. Creating Application Functionality</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><A accesskey="N" href="index.lxp@lxpwrap=x5925_252ehtm.htm">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1">The document</A></H1><P>The <TTCLASS="CLASSNAME">KalamDocument</TT> document class is a simple wrapper around a <TTCLASS="CLASSNAME">QString</TT> object. The reason for using a <TTCLASS="CLASSNAME">QString</TT> to hold all text, instead of a Python string object, is straight-forward: with all the passing around of strings, converting the <TTCLASS="CLASSNAME">QString</TT>s retrieved from the <TTCLASS="CLASSNAME">QMultiLineEdit</TT> widgets to Python strings would take far too much time. String conversion is a fairly costly operation, involving the copying of potentially large amounts of memory.</P><P>There is another reason for using <TTCLASS="CLASSNAME">QString</TT>in this manner: a <TTCLASS="CLASSNAME">QString</TT> is mutable, and a Python string not. This means, simply put, that every time you change a single character in a Python string, a complete new copy of the string is made, and the old copy is discarded.</P><P>There are good reasons for this behavior. If Python strings were mutable, they could not be used to index Python dictionaries based on their character value, but only on the abstract object ID that all Python objects receive. Imagine the mess you would have if you changed the actual value of a key in a dictionary.</P><P><TTCLASS="CLASSNAME">QString</TT> is a clever and optimized class. If two instances of <TTCLASS="CLASSNAME">QString</TT> have the same contents, there is a good chance that they will even share the memory needed to store the actual text. Furthermore, <TTCLASS="CLASSNAME">QString</TT> offers as rich a set of methods to mangle strings as Python does, so we don't lose much functionality. (But look carefully at the documentation for <TTCLASS="CLASSNAME">QString</TT> — some functions, such as <TTCLASS="FUNCTION">stripWhiteSpace()</TT>, return a new string instead of working on the existing string.)</P><P>Would our editor have to store more complex information, instead of plain text, we should use the <TTCLASS="CLASSNAME">KalamDocument</TT> class to store its data perhaps in a list of paragraphs, where each paragraph is a list itself, containing words, lines and perhaps more complex objects, such as images or even active widgets — so you could embed a button or a hyperlink in your text. However, never code what you don't yet need is a excellent motto...</P><PRECLASS="PROGRAMLISTING">"""kalamdoc.py - abstraction of a document with a certain encodingcopyright: (C) 2001, Boudewijn Remptemail: boud@rempt.xs4all.nl"""from qt import *from resources import TRUE, FALSEclass KalamDoc(QObject): """ The document represents a plain text with a certain encoding. Default is Unicode. signals: sigDocModified (boolean) sigDocTitleChanged (string) sigDocTextChanged (qstring, qwidget) """ def __init__(self, *args): apply(QObject.__init__, (self,)+args) self.encoding="unicode" self.newDocument() self._fileName = None self._title = "Untitled" self._modified = FALSE self._text = QString() </PRE><P>Instead of wrapping a simple, silly boolean value, we now wrap s single <TTCLASS="CLASSNAME">QString</TT> object.</P><PRECLASS="PROGRAMLISTING"> def setText(self, text, view=None): self._text=text self._modified=TRUE self.emit(PYSIGNAL("sigDocTextChanged"), (self._text, view)) </PRE><P>Most of the above functions haven't changed the basic framework. Note that the <TTCLASS="FUNCTION">slotModified</TT> function has disappeared. Modifying a text isn't as simple as flipping a single boolean.</P><P>The <TTCLASS="FUNCTION">setText</TT> function, which is called from the <TTCLASS="CLASSNAME">KalamView</TT> class, applies brute force to the text that <TTCLASS="CLASSNAME">KalamDocument</TT> manages. Quite simply, <TTCLASS="FUNCTION">setText</TT> replaces the internal reference to <TTCLASS="CLASSNAME">QString</TT> with a reference to the <TTCLASS="CLASSNAME">QString</TT> that was presented by the calling view. The text has been modified, and this is recorded in the administrative <TTCLASS="VARNAME">_modified</TT> variable. Finally, by emitting the <TTCLASS="VARNAME">"sigDocTextChanged"</TT> Python signal, all views that show this document are told to update their display.</P><P>The <TTCLASS="VARNAME">view</TT> parameter has a default value of <TTCLASS="VARNAME">None</TT> — this means the change does not originate with any view, and will be applied to all views.</P></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><A accesskey="P" href="index.lxp@lxpwrap=x5798_252ehtm.htm">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><A accesskey="H" href="index.lxp@lxpwrap=book1_252ehtm">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><A accesskey="N" href="index.lxp@lxpwrap=x5925_252ehtm.htm">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">The view</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><A accesskey="U" href="index.lxp@lxpwrap=c5783_252ehtm.htm">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Saving and loading documents</TD></TR></TABLE></DIV></BODY></HTML> </td> </tr> </table> </td> </tr> </table> ⌨️ 快捷键说明
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