Question

I have a Qt application with an embedded script/jit. Now I’d like to receive the output from the script on an QTextEdit (more specific QPlainTextEdit). For this purpose callbacks are being issued. The problem I’m facing is that whatever I try the output to the TextEdit is either delayed until the script has finished or gets stuck after 2-3 seconds (and is delayed then until the script has finished).
I tried to use signals and slots for the update but also direct function calls – neither worked. Also repainting / updating the TextEdit and the parent form as well as even QCoreApplication::flush() did show little/no effect. Seems like I’m doing something fundamentally wrong. Any ideas or examples how to achive the “real time” updates?

Btw, the update routines are being called – debug output to stdout is avaiable in real time.

Answer 1

Just to sketch a soluting using threads, which I have used numerous times for logging purposes and which works as desired:

Define your thread class:

class MyThread : public QThread
{
  Q_OBJECT
public:
  MyThread(QObject *parent=0) : QThread(parent) {}
signals:
  void signalLogMessage(const QString &logMessage);

...
};

Whenever you want a log message to be shown in the main thread, just use

emit signalLogMessage("Foo!");

In your main thread:

MyThread *thread = new MyThread(this);
connect(thread, SIGNAL(signalLogMessage(const QString&)), 
        this, SLOT(logMessageFromThread(const QString&)));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
...
thread->start();

where logMessageFromThread does something like myPlainTextEdit->appendPlainText(message).
This works without any delay or other problems.

I hope that helps.