CODEWITHSUNDEEP
qt
nils
nils

Reputation: 1402

Forward value from signals within a QStateMachine

I am currently having trouble with a QStateMachine in QT. Basically I want to use it to control the flow between my screens, e.g. to switch from a master page to a detail page.

What I basically have is this:

// Overview
QState* overviewState = new QState();
overviewState->assignProperty(ui->stackedWidget, "currentIndex", 0);
stateMachine->addState(overviewState);

// Editor
QState* editorState = new QState();
editorState ->assignProperty(ui->stackedWidget, "currentIndex", 1);
stateMachine->addState(editorState);

// Overview -> Editor
overviewState->addTransition(overview, SIGNAL(onEditor()), editorState);

So far this is working as expected. The overview emits onEditor and the editor is shown. However, now I want to forward a value from the signal. The editor can be called with a selected value (meaning the user wants to edit an entry) or without a value (meaning the user starts with an empty editor). The overview would then have two signals: onEditor and onEditor(long). The editor would have two slots: performInitialize and performInitialize(long). 

connect(editorState, SIGNAL(entered()), editor, SLOT(performInitialize()));

This is the point where I am stuck. (How) can I forward the signal from onEditor(long) to performInitialize(long)? The signal from the QState surely has no knowledge of this additional parameter. How can I solve this?

Thanks a lot in advance.

Upvotes: 1

Views: 172

Answers (1)

Kuba hasn't forgotten Monica
Kuba hasn't forgotten Monica

Reputation: 98505

You can split the initialization into setup and performance stages:

void Editor::performInitialize(long val); // current implementation - keep it

void Editor::setupInitialize(long val);
  m_initVal = val;
}

void Editor::performInitialize() {
  performInitialize(m_initVal);
}

connect(overview, SIGNAL(onEditor(long)), editor, SLOT(setupInitialize(long)));
overviewState->addTransition(overview, SIGNAL(onEditor(long)), editorState);

addTransition sets up an internal connection to the signal. Qt guarantees that slots are executed in the order of connection. Thus the state transition is guaranteed never to precede setupInitialize call.

Upvotes: 1

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