[Qt-interest] please help me with this problem

[Nikos Chantziaras]

On 12/07/2009 08:06 PM, Yifei Li wrote:
> Hi folks,
>
> In my thread's run() method, signal displayMessage(QString) is emitted and the signal is connected to a slot setMessage(QString) in a QGraphicsScene object (using direct connection)
>
> // run method looks like this:
> void run()
> {
>     sleep(2);
>     emit displayMessage("hello 1");
>     sleep(2);
>     emit displayMessage("hello 2");
>     sleep(2);
>     emit displayMessage("hello 3");
> }
>
> // Here is what setMessage(QString) looks like:
> void setMessage(QString msg)
> {
>       m_message = msg;    // save the message
>       update();
> }
>
> The message is then displayed in drawForegound method
>
>
> However, my problem is 'hello1' and 'hello2' don't show up at all, only 'hello3' does.
>
> My guess is that update() queues the paint event and several paint events are merged into one due to optimization, so what should I do make those three messages displayed one after another?

I think your problem is that sleep() blocks.  That means, the 
application actually "hangs" for 2 seconds between each sleep() with no 
chance to update the display.

You should use timers instead of sleep().  See 
http://doc.trolltech.com/4.6/qtimer.html#details on how to emit signals 
with a time delay or periodically.