[Qt-interest] Fwd: QThread() examples

[Sean Harmer]

On Friday 19 December 2008 04:43:21 chandrasekar wagmare wrote:
> thank you very much .... same thing my boss told to me  no use of changing
> GUI part in worker thread but what can i do ?... in my program one slot is
> running too long so in between the slot i try to update the text of QLabel
> to change but after the slot/event over only it repaints so i need to
> switch to thread but here now new problem came telling cant change the GUI
> in worker thread ...  how can i resolve it ... please help ...  i will 
> look over the Qt Mandelbrot  example  now and any way
Although it is true that you can't directly update the GUI from a worker 
thread, you can of course trigger an update to happen in the main thread. The 
trick is to get your worker thread to emit a signal whenever you wish to cause 
an update e.g. to a label or a progress bar. Then connect to this signal to an 
object in the main thread that actually performs the update on the GUI. Please 
check out the section on queued connections:

http://doc.trolltech.com/4.4/threads.html#signals-and-slots-across-threads

The Mandelbrot example you are looking at uses this technique. It "sends" the 
QImage via the signal to the main thread for it to be painted on the screen. 
In your case you may only be sending some progress info via a signal that you 
emit periodically.

HTH,

Sean