echowindow.cpp Example File
tools/echoplugin/echowindow/echowindow.cpp

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 #include <QtGui>

 #include "echowindow.h"

 EchoWindow::EchoWindow()
 {
     createGUI();
     setLayout(layout);
     setWindowTitle("Echo Plugin Example");

     if (!loadPlugin()) {
         QMessageBox::information(this, "Error", "Could not load the plugin");
         lineEdit->setEnabled(false);
         button->setEnabled(false);
     }
 }

 void EchoWindow::sendEcho()
 {
     QString text = echoInterface->echo(lineEdit->text());
     label->setText(text);
 }

 void EchoWindow::createGUI()
 {
     lineEdit = new QLineEdit;
     label = new QLabel;
     label->setFrameStyle(QFrame::Box | QFrame::Plain);
     button = new QPushButton(tr("Send Message"));

     connect(lineEdit, SIGNAL(editingFinished()),
             this, SLOT(sendEcho()));
     connect(button, SIGNAL(clicked()),
             this, SLOT(sendEcho()));

     layout = new QGridLayout;
     layout->addWidget(new QLabel(tr("Message:")), 0, 0);
     layout->addWidget(lineEdit, 0, 1);
     layout->addWidget(new QLabel(tr("Answer:")), 1, 0);
     layout->addWidget(label, 1, 1);
     layout->addWidget(button, 2, 1, Qt::AlignRight);
     layout->setSizeConstraint(QLayout::SetFixedSize);
 }

 bool EchoWindow::loadPlugin()
 {
     QDir pluginsDir(qApp->applicationDirPath());
 #if defined(Q_OS_WIN)
     if (pluginsDir.dirName().toLower() == "debug" || pluginsDir.dirName().toLower() == "release")
         pluginsDir.cdUp();
 #elif defined(Q_OS_MAC)
     if (pluginsDir.dirName() == "MacOS") {
         pluginsDir.cdUp();
         pluginsDir.cdUp();
         pluginsDir.cdUp();
     }
 #endif
     pluginsDir.cd("plugins");
     foreach (QString fileName, pluginsDir.entryList(QDir::Files)) {
         QPluginLoader pluginLoader(pluginsDir.absoluteFilePath(fileName));
         QObject *plugin = pluginLoader.instance();
         if (plugin) {
             echoInterface = qobject_cast<EchoInterface *>(plugin);
             if (echoInterface)
                 return true;
         }
     }

     return false;
 }