Google Suggest Example

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.

 #include "googlesuggest.h"

 #define GSUGGEST_URL "http://google.com/complete/search?output=toolbar&q=%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 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 itemClicked() signal with the 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 finished() signal with the handleNetworkData() slot to handle the incoming data.

 GSuggestCompletion::GSuggestCompletion(QLineEdit *parent): QObject(parent), editor(parent)
 {
     popup = new QTreeWidget;
     popup->setWindowFlags(Qt::Popup);
     popup->setFocusPolicy(Qt::NoFocus);
     popup->setFocusProxy(parent);
     popup->setMouseTracking(true);

     popup->setColumnCount(2);
     popup->setUniformRowHeights(true);
     popup->setRootIsDecorated(false);
     popup->setEditTriggers(QTreeWidget::NoEditTriggers);
     popup->setSelectionBehavior(QTreeWidget::SelectRows);
     popup->setFrameStyle(QFrame::Box | QFrame::Plain);
     popup->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
     popup->header()->hide();

     popup->installEventFilter(this);

     connect(popup, SIGNAL(itemClicked(QTreeWidgetItem*,int)),
             SLOT(doneCompletion()));

     timer = new QTimer(this);
     timer->setSingleShot(true);
     timer->setInterval(500);
     connect(timer, SIGNAL(timeout()), SLOT(autoSuggest()));
     connect(editor, SIGNAL(textEdited(QString)), timer, SLOT(start()));

     connect(&networkManager, SIGNAL(finished(QNetworkReply*)),
             this, SLOT(handleNetworkData(QNetworkReply*)));

 }

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.

 GSuggestCompletion::~GSuggestCompletion()
 {
     delete popup;
 }

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.

 bool GSuggestCompletion::eventFilter(QObject *obj, QEvent *ev)
 {
     if (obj != popup)
         return false;

     if (ev->type() == QEvent::MouseButtonPress) {
         popup->hide();
         editor->setFocus();
         return true;
     }

     if (ev->type() == QEvent::KeyPress) {

         bool consumed = false;
         int key = static_cast<QKeyEvent*>(ev)->key();
         switch (key) {
         case Qt::Key_Enter:
         case Qt::Key_Return:
             doneCompletion();
             consumed = true;

         case Qt::Key_Escape:
             editor->setFocus();
             popup->hide();
             consumed = true;

         case Qt::Key_Up:
         case Qt::Key_Down:
         case Qt::Key_Home:
         case Qt::Key_End:
         case Qt::Key_PageUp:
         case Qt::Key_PageDown:
             break;

         default:
             editor->setFocus();
             editor->event(ev);
             popup->hide();
             break;
         }

         return consumed;
     }

     return false;
 }

The 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.

 void GSuggestCompletion::showCompletion(const QStringList &choices, const QStringList &hits)
 {

     if (choices.isEmpty() || choices.count() != hits.count())
         return;

     const QPalette &pal = editor->palette();
     QColor color = pal.color(QPalette::Disabled, QPalette::WindowText);

     popup->setUpdatesEnabled(false);
     popup->clear();
     for (int i = 0; i < choices.count(); ++i) {
         QTreeWidgetItem * item;
         item = new QTreeWidgetItem(popup);
         item->setText(0, choices[i]);
         item->setText(1, hits[i]);
         item->setTextAlignment(1, Qt::AlignRight);
         item->setTextColor(1, color);
     }
     popup->setCurrentItem(popup->topLevelItem(0));
     popup->resizeColumnToContents(0);
     popup->resizeColumnToContents(1);
     popup->adjustSize();
     popup->setUpdatesEnabled(true);

     int h = popup->sizeHintForRow(0) * qMin(7, choices.count()) + 3;
     popup->resize(popup->width(), h);

     popup->move(editor->mapToGlobal(QPoint(0, editor->height())));
     popup->setFocus();
     popup->show();
 }

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 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 editor QLineEdit emit the returnPressed() signal, to which the application can connect to open the respective web page.

 void GSuggestCompletion::doneCompletion()
 {
     timer->stop();
     popup->hide();
     editor->setFocus();
     QTreeWidgetItem *item = popup->currentItem();
     if (item) {
         editor->setText(item->text(0));
         QMetaObject::invokeMethod(editor, "returnPressed");
     }
 }

The 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 get() function to start the request.

 void GSuggestCompletion::autoSuggest()
 {
     QString str = editor->text();
     QString url = QString(GSUGGEST_URL).arg(str);
     networkManager.get(QNetworkRequest(QString(url)));
 }

The function preventSuggest() stops the timer to prevent further requests from being started.

 void GSuggestCompletion::preventSuggest()
 {
     timer->stop();
 }

When the network request is finished, the QNetworkAccessManager delivers the data received from the server through the networkReply object.

 void GSuggestCompletion::handleNetworkData(QNetworkReply *networkReply)
 {
     QUrl url = networkReply->url();
     if (!networkReply->error()) {
         QStringList choices;
         QStringList hits;

         QByteArray response(networkReply->readAll());
         QXmlStreamReader xml(response);
         while (!xml.atEnd()) {
             xml.readNext();
             if (xml.tokenType() == QXmlStreamReader::StartElement)
                 if (xml.name() == "suggestion") {
                     QStringRef str = xml.attributes().value("data");
                     choices << str.toString();
                 }
             if (xml.tokenType() == QXmlStreamReader::StartElement)
                 if (xml.name() == "num_queries") {
                     QStringRef str = xml.attributes().value("int");
                     hits << str.toString();
                 }
         }

         showCompletion(choices, hits);
     }

     networkReply->deleteLater();
 }

To extract the data from the reply we use the 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 deleteLater function.

 #include <QLineEdit>

 class GSuggestCompletion;

 class SearchBox: public QLineEdit
 {
     Q_OBJECT

 public:
     SearchBox(QWidget *parent = 0);

 protected slots:
     void doSearch();

 private:
     GSuggestCompletion *completer;

 SearchBox::SearchBox(QWidget *parent): QLineEdit(parent)
 {
     completer = new GSuggestCompletion(this);

     connect(this, SIGNAL(returnPressed()),this, SLOT(doSearch()));

     setWindowTitle("Search with Google");

     adjustSize();
     resize(400, height());
     setFocus();
 }

 void SearchBox::doSearch()
 {
     completer->preventSuggest();
     QString url = QString(GSEARCH_URL).arg(text());
     QDesktopServices::openUrl(QUrl(url));
 }