[Qt-interest] signals and slots, combination and execution order

[John McClurkin]

hilbert at beuth-hochschule.de wrote:
> hello,
> 
> i have a QLineEdit with the signal 'editingFinished()' connected to 'slot1
> ()'. there is also a QPushButton with the signal 'clicked()' connected to 
> another 'slot2()'. as to be expected: when the text in the QLineEdit is 
> changed and the QPushButton ist clicked both slots are executed. in my 
> case 'slot1()' is always called first. in some cases i need to execute a 
> QMessegeBox::question(...) in 'slot1()' and wait for the return value of the 
> question box. if this is the case, the QPushButton hangs (at least visually) 
> in the 'pressed' state and 'slot2()' is never called. the 'clicked()'-signal 
> of the QPushButton seems to be lost even when the connection is set to 
> Qt::QueuedConnection. is there an easy or at least a reasonable way to solve 
> this problem without tricky event-handling?
> 
> no other threads than the main-gui-thread are involved at this stage of the 
> programm. i already tested a bit with an event filter. as far as i got the 
> event for the button release seems to be eaten up by the modal 
> QMessegeBox::question dialog. for me it would be awkward to ask for any 
> QPushButton states in slot1 (and when to do this would generate further 
> difficulties)...
> 
> and how could i possibly determine the order of the calls?
> 
> thanx & best regards,
> andreas
> --
> Open WebMail Project (http://openwebmail.org)
I think you have a basic problem with this design. According to the 
docs, a button's clicked signal is emitted when the button is released, 
but QLineEdit object will loose focus and emit its editingFinished 
signal when the button is pressed. Because you are posting a modal 
dialog in the slot connected to the editingFinished signal, the clicked 
signal from the button is lost.