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/****************************************************************************
**
** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example network/googlesuggest
\title Google Suggest Example
The Google Suggest example demonstrates how to use the QNetworkAccessManager
class to obtain a list of suggestions from the Google search engine as the
user types into a QLineEdit.
\image googlesuggest-example.png
The application makes use of the \c get function in
QNetworkAccessManager to post a request and obtain the result of the search
query sent to the Google search engine. The results returned are listed as
clickable links appearing below the search box as a drop-down menu.
The widget is built up by a QLineEdit as the search box, and a QTreeView
used as a popup menu below the search box.
\section1 GSuggestCompletion Class Declaration
This class implements an event filter and a number of functions to display
the search results and to determent when and how to perform the search.
\snippet examples/network/googlesuggest/googlesuggest.h 1
The class connects to a QLineEdit and uses a QTreeWidget to display the
results. A QTimer controls the start of the network requests that are
executed using a QNetworkAccessManager.
\section1 GSuggestCompletion Class Implementation
We start by defining a constant containing the URL to be used in the Google
queries. This is the basis for the query. The letters typed into the search
box will be added to the query to perform the search itself.
\snippet examples/network/googlesuggest/googlesuggest.cpp 1
In the constructor, we set the parent of this GSuggestCompletion instance
to be the QLineEdit passed in. For simplicity, the QLineEdit is also stored
in the explicit \c editor member variable.
We then create a QTreeWidget as a toplevel widget and configure the various
properties to give it the look of a popup widget.
The popup will be populated by the results returned from Google. We set
the number of columns to be two, since we want to display both the
suggested search term and the number of hits it will trigger in the search
engine.
Furthermore, we install the GSuggestCompletion instance as an event filter
on the QTreeWidget, and connect the \c itemClicked() signal with the \c
doneCompletion() slot.
A single-shot QTimer is used to start the request when the user has stopped
typing for 500 ms.
Finally, we connect the networkManagers \c finished() signal with the \c
handleNetworkData() slot to handle the incoming data.
\snippet examples/network/googlesuggest/googlesuggest.cpp 2
Since the QTreeWidget popup has been instantiated as a toplevel widget, the
destructor has to delete it explicitly from memory to avoid a memory leak.
\snippet examples/network/googlesuggest/googlesuggest.cpp 3
The event filter handles mouse press and key press events that are
delivered to the popup. For mouse press events we just hide the popup and
return focus to the editor widget, and then return true to prevent further
event processing.
Key event handling is implemented so that Enter and Return execute the
selected link, while the Escape key hides the popup. Since we want to be
able to navigate the list of suggestions using the different navigation
keys on the keyboard we let Qt continue regular event processing for those
by returning false from the eventFilter reimplementation.
For all other keys, the event will be passed on to the editor widget and the
popup is hidden. This way the user's typing will not be interrupted by the
popping up of the completion list.
\snippet examples/network/googlesuggest/googlesuggest.cpp 4
The \c showCompletion() function populates the QTreeWidget with the results
returned from the query. It takes two QStringLists, one with the suggested
search terms and the other with the corresponding number of hits.
\snippet examples/network/googlesuggest/googlesuggest.cpp 5
A QTreeWidgetItem is created for each index in the list and inserted into
the QTreeWidget. Finally, we adjust position and size of the popup to make
sure that it pops up in the correct position below the editor, and show it.
The \c doneCompletion() function, which is called by the event filter when
either Enter or Return keys are pressed, stops the timer to prevent further
requests and passes the text of the selected item to the editor. We then
make the \c editor QLineEdit emit the returnPressed() signal, to which the
application can connect to open the respective web page.
\snippet examples/network/googlesuggest/googlesuggest.cpp 6
The \c autoSuggest() slot is called when the timer times out, and uses the
text in the editor to build the complete search query. The query is then
passed to the QNetworkAccessManager's \c get() function to start the
request.
\snippet examples/network/googlesuggest/googlesuggest.cpp 7
The function \c preventSuggest() stops the timer to prevent further
requests from being started.
\snippet examples/network/googlesuggest/googlesuggest.cpp 8
When the network request is finished, the QNetworkAccessManager delivers the
data received from the server through the networkReply object.
\snippet examples/network/googlesuggest/googlesuggest.cpp 9
To extract the data from the reply we use the \c readAll() function, which
is inherited from QIODevice and returns a QByteArray. Since this data is
encoded in XML we can use a QXmlStreamReader to traverse the data and
extract the search result as QStrings, which we can stream into two
QStringLists used to populate the popup.
Finally, we schedule the QNetworkReply object for deletion using the \c
deleteLater function.
\section1 SearchBox Class Declaration
The SearchBox class inherits QLineEdit and adds the protected slot \c
doSearch().
A \c GSuggestCompletion member provides the SearchBox with the request
functionality and the suggestions returned from the Google search engine.
\snippet examples/network/googlesuggest/searchbox.h 1
\section1 SearchBox Class Implementation
The search box constructor instantiates the GSuggestCompletion object and
connects the returnPressed() signal to the doSearch() slot.
\snippet examples/network/googlesuggest/searchbox.cpp 1
The function \c doSearch() stops the completer from sending any further
queries to the search engine.
Further, the function extracts the selected search phrase and opens it
in the default web browser using QDesktopServices.
\snippet examples/network/googlesuggest/searchbox.cpp 2
*/
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