QStateMachine and GUI update in a QState::onExit()

DerekDomino

Hello,

I'm using QStateMachine with several sets of subclassed QState's.

In one of these, I'm overriding onExit() to make some work when exiting the state. This work is long (about 2 secs) and I would like to update the GUI in order to tell the user that some work is on going. A QStackedLayout is used: one of the layer is shown and the text of a QLabel (inside the QWidget/layer of the stacked layout) is then set at the beginning of onExit(), before the hard work.

Unfortunately, the GUI is updated later by when onExit() is over and after -I guess- some Qt internal loop/statemachine work.

I tried to force to update() the widget or processEvents() (QApplication), but was unsuccessful.

Do you have any hint about updating the GUI in onExit()?

Thanks

Santosh Reddy

qApp->processEvents() should work. Can you show a snippet of it?

DerekDomino

Hi,

Here it is:
@
void ToolbarShownState::onExit(QEvent * /event/) {
// sets the text of a QLabel
statusWidget->setProperty("statusText", tr("Closing ..."));

// shows the statusWidget
stackedLayout->setCurrentIndex(1);

// trying to refresh the GUI
myQApp->processEvents();
//statusWidget->update();
//stackedLayout->update();

// Do some heavy work here
// can last several seconds
...
}
@
The setProperty is called since I can see in the console the qDebug() output it logs.

I have other states where the same problem is encountered, GUI refreshes only when QStateMachine finishes its duty.

The heavy work could be deferred in a call executed later with QTimer + 0 second delay or a connect() with a QueuedConnection, but it is not clear to me when the slot will be executed:

just after onExit()?
after QStateMachine has finished all its work (e.g., after entering into the next state, that would be a disaster)?
randomly?

Santosh Reddy

What is statusWidget?
If statusWidget is a QLabel then use "text" instead of "statusText"

DerekDomino

I have subclassed QWidget, added it a QLabel, some methods and properties. Before this call the the QLabel has already a value (a different one).

The second call (stackedLayout->setCurrentIndex(1);) doesn't trigger GUI update neither. The role of this call is to raise the statusWidget in stack.

Santosh Reddy

I hope you have properly registered the property, and are handleing the QLabel text settings accordingly.

Also whats with myQApp? are you sure that is not a problem?