[ fromfile: qprocess.xml id: qonsole ]

A command-line shell reads commands from the user and prints the output. In this example, we have a QTextEdit providing a view of the output of another running process, in this case, bash^[101], the default command-line shell interpreter for most systems. The QProcess is a model, representing a running process. Figure 17.4 shows a screenshot of Qonsole, our first attempt at a GUI for a command shell.^[102]

Figure 17.4. Qonsole1

Because it connects signals to slots and handles user interactions, Qonsole is considered a controller. Because it derives from QMainWindow, it also contains some view code. The UML diagram in Figure 17.5 shows the relationships between the classes in this application.

Figure 17.5.  Qonsole UML: Model and View

Example 17.6 shows the class definition for Qonsole.

[ . . . . ]
class Qonsole : public QMainWindow {
    Q_OBJECT
 public:
    Qonsole();
 public slots:
    void execute();
    void showOutput();
 private:
    QTextEdit* m_Logw;
    QLineEdit* m_InputArea;
    QProcess* m_Shell;
};
[ . . . . ]

Example 17.7 shows the how constructor establishes the structure of Qonsole and the important connections between its components.

[ . . . . ]

Qonsole::Qonsole() {
   m_Logw = new QTextEdit();
   m_Logw->setReadOnly(true);
   setCentralWidget(m_Logw);
   m_InputArea = new  QLineEdit();
   QDockWidget* qdw = new QDockWidget("Type commands here");
   qdw->setWidget(m_InputArea);
   addDockWidget(Qt::BottomDockWidgetArea, qdw);
   connect (m_InputArea, SIGNAL(returnPressed()),
			this, SLOT(execute()));

   m_Shell = new QProcess(this);
   m_Shell->setReadChannelMode(QProcess::MergedChannels);           
   connect (m_Shell, SIGNAL(readyReadStandardOutput()),
			 this, SLOT(showOutput()));
#ifdef Q_OS_WIN
   m_Shell->start("cmd", QStringList(), QIODevice::ReadWrite);
#else
   m_Shell->start("bash", QStringList("-i"), QIODevice::ReadWrite); 
#endif

}

Whenever the shell outputs anything, Qonsole sends it to the QTextEdit. Whenever the user presses the return key, Qonsole grabs any text that is in the QLineEdit and sends it to the shell, which interprets it as a command, as shown in Example 17.8.

[ . . . . ]

void Qonsole::showOutput() {            
    QByteArray bytes = m_Shell->readAllStandardOutput();
    QStringList lines = QString(bytes).split("\n");
    foreach (QString line, lines) {
        m_Logw->append(line);
    }
}

void Qonsole::execute() {
    QString cmdStr = m_InputArea->text() + "\n";
    m_InputArea->setText("");
    m_Logw->append(cmdStr);
    QByteArray bytes = cmdStr.toUtf8(); 
    m_Shell->write(bytes);               
}

Example 17.9 shows the client code that launches this application.

[ . . . . ]

#include <QApplication>

int main(int argc, char* argv[]) {
   QApplication app(argc, argv);
   Qonsole qon;
   qon.show();
   return app.exec();
}