The QStatusBar has just one line each time and I cannot track the history or save the history in a log file.
So I want to have a dock widget in my mainwindow that is able to display the messages I need in a multi-line way and auto-scrolling way and then automatically saved to a log file.
My question is how to do this in Qt?
If what you are looking for is something similar to the "Application Output" pane of QtCreator, then a simple QPlainTextEdit can do the job. You can call QPlainTextEdit::setReadOnly(true) if you don't want the user to be able to edit its content (i.e. only your application can write to it).
If you want auto-scrolling and automatically saving to a log file, you will need to subclass it though. Here's a little something to get you started:
#include <QCoreApplication>
class MyLogWindow : public QPlainTextEdit
{
Q_OBJECT
/* snip */
public:
void appendMessage(const QString& text);
private:
QFile m_logFile;
};
void MyLogWindow::appendMessage(const QString& text)
{
this->appendPlainText(text); // Adds the message to the widget
this->verticalScrollBar()->setValue(this->verticalScrollBar()->maximum()); // Scrolls to the bottom
m_logFile.write(text); // Logs to file
// optional if you want to see the changes
// after appendPlainText() immediately
// useful if you use this->appendMessage() in a loop
QCoreApplication::processEvents();
}
I leave it to you to deal with the boilerplate (opening and closing the file, dealing with newlines, etc.).
Now, simply put an instance of MyLogWindow in a dock in your QMainWindow, and call MyLogWindow::appendMessage() every time you need to log something to have it displayed, scrolled and saved automatically.
