QListView force redraw.

[Dave Stewart]

Hi there, first post to the forums. Hope someone can help me.

I have a list view which is populated by any of a number of background threads (mutex locked of course ;-). The problem I have is that the list view only redraws with the new rows when I resize it (it's in a docking window).

I guess I need to emit a signal to get it to redraw but I've tried every signal I can find and still no joy. Code sample follows. What am I doing wrong. I guess I need to get the main event loop to fire but how do I send an appropriate event from another thread?

class MessageList : public QListWidget 
{
Q_OBJECT
public:
	MessageList(QWidget* pW) : QListWidget(pW) {}
 
	void logMessage(const std::string& sMessage) {
		boost::mutex::scoped_lock scoped_lock(m_oMessageListMutex);
		QListWidgetItem *item = new QListWidgetItem(sMessage.c_str(), this);
		setCurrentItem (item);
		update();
		emit itemChanged(item);
		emit itemActivated (item);
		emit itemClicked (item);
		emit itemDoubleClicked (item);
		emit itemEntered (item);
		emit itemPressed (item);
	}
 
protected:
	boost::mutex m_oMessageListMutex;
};

class MessageList : public QListWidget 
{
Q_OBJECT
public:
	MessageList(QWidget* pW) : QListWidget(pW) {}

	void logMessage(const std::string& sMessage) {
		boost::mutex::scoped_lock scoped_lock(m_oMessageListMutex);
		QListWidgetItem *item = new QListWidgetItem(sMessage.c_str(), this);
		setCurrentItem (item);
		update();
		emit itemChanged(item);
		emit itemActivated (item);
		emit itemClicked (item);
		emit itemDoubleClicked (item);
		emit itemEntered (item);
		emit itemPressed (item);
	}

protected:
	boost::mutex m_oMessageListMutex;
};

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Many thanks
Dave

[wysota]

I have a list view which is populated by any of a number of background threads (mutex locked of course ;-).

That won't work. Mutex or no mutex... You can't update the list from within external threads. Instead emit a signal from other threads that will be connected to a custom slot in the view that will add the items. You won't need any special treatment then.

[Dave Stewart]

That won't work. Mutex or no mutex... You can't update the list from within external threads. Instead emit a signal from other threads that will be connected to a custom slot in the view that will add the items. You won't need any special treatment then.

Hi wysota, thanks for the reply. Your suggestion seems straight forward enough but I can't get it to work.

I've defined the following in MainWindow.h in class MainWindow

void logMessage(const std::string& sMessage) {
		boost::mutex::scoped_lock scoped_lock(m_oMessageListMutex);
		emit logMessageSignal(QString(sMessage.c_str()));
	}
 
signals:
	void logMessageSignal(QString& sMessage);
 
public slots:
	void messageReceived(QString& sMessage) {
		QListWidgetItem *item = new QListWidgetItem(sMessage, messagesListWidget);
	}

void logMessage(const std::string& sMessage) {
		boost::mutex::scoped_lock scoped_lock(m_oMessageListMutex);
		emit logMessageSignal(QString(sMessage.c_str()));
	}

signals:
	void logMessageSignal(QString& sMessage);

public slots:
	void messageReceived(QString& sMessage) {
		QListWidgetItem *item = new QListWidgetItem(sMessage, messagesListWidget);
	}

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logMessage() is called from the worker threads.

In MainWindow.cpp I have connected as follows (called from the main thread):

connect(this, SIGNAL(logMessageSignal(QString& sMessage)), this, SLOT(messageReceived(QString& sMessage)));

connect(this, SIGNAL(logMessageSignal(QString& sMessage)), this, SLOT(messageReceived(QString& sMessage)));

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I get a runtime error:

Object::connect: No such signal MainWindow::logMessageSignal(QString&sMessage)
Object::connect: (sender name: 'MainWindow')
Object::connect: (receiver name: 'MainWindow')

cheers
Dave

[wysota]

Don't pass parameter names into signal and slot signatures.

http://www.qtcentre.org/forum/faq.ph...lot_with_names

[Dave Stewart]

Don't pass parameter names into signal and slot signatures.

http://www.qtcentre.org/forum/faq.ph...lot_with_names

Thanks for that. I'll check the FAQS first in future.

Cheers
Dave