Native Development

[hungcotac]

I want to create Timeout slot:

file TestYourReflex.hpp

#ifndef TestYourReflex_HPP_
#define TestYourReflex_HPP_

#include <QObject>
#include <QTimer>
#include <QTime>


namespace bb { namespace cascades { class Application; }}

/*!
 * @brief Application pane object
 *
 *Use this object to create and init app UI, to create context objects, to register the new meta types etc.
 */
class TestYourReflex : public QObject
{
    Q_OBJECT
public:
    TestYourReflex(bb::cascades::Application *app);
    virtual ~TestYourReflex() {};
public slots:
    void Timeout(int a);

};


#endif /* TestYourReflex_HPP_ */

file TestYourReflex.cpp

// Default empty project template
#include "TestYourReflex.hpp"

#include <bb/cascades/Application>
#include <bb/cascades/QmlDocument>
#include <bb/cascades/AbstractPane>
#include <bb/cascades/Container>
#include <bb/cascades/Color>

using namespace bb::cascades;

TestYourReflex::TestYourReflex(bb::cascades::Application *app) :
		QObject(app) {
	// create scene document from main.qml asset
	// set parent to created document to ensure it exists for the whole application lifetime
	QmlDocument *qml = QmlDocument::create("asset:///main.qml").parent(this);

	// create root object for the UI
	AbstractPane *root = qml->createRootObject<AbstractPane>();
	QTimer *timer = new QTimer(this);
	timer->setInterval(1000);
	timer->start();
	connect(timer, SIGNAL(timeout()), this, SLOT(Timeout(seed)));
	// set created root object as a scene
	app->setScene(root);
}

void TestYourReflex::Timeout(QTimer *timer){
	qDebug() << "timeout";
	timer->stop();


}

 when the Timeout() function doesn't have param QTimer * timer this code work very well. but when I pass QTimer *timer param like above. the code doesn't work and a got this ERROR 

NOTICE Object::connect: No such slot TestYourReflex::Timeout(seed) in ../src/TestYourReflex.cpp:23

any one can help me 

[Zmey · Accepted solution]

You can't pass additional parameters to slots. Their signatures must be the same as signal signatures.

It's allowed to omit signal parameters in slots, but changing any of the types or passing additional data is not allowed.

In this case a possible solution is declaring QTimer * in the header file as a member variable.

Declare other variables which you need to access in multiple functions the same way.

Don't forget to remove 'int a' in slot params or it won't work:

class QTimer;

class TestYourReflex : public QObject
{
    Q_OBJECT
public:
    TestYourReflex(bb::cascades::Application *app);
    virtual ~TestYourReflex() {};
public slots:
    void onTimeout();

protected:
    QTimer *timer_;
};

 In .cpp:

	timer_ = new QTimer(this);
	timer_->setInterval(1000);
	timer_->start();
        QObject::connect(timer_, SIGNAL(timeout()), this, SLOT(onTimeout()));

 ...

void TestYourReflex::onTimeout(){
	qDebug() << "timeout";
	timer_->stop();
}

P.s. There's also QTimer::singleShot(1000, this, SLOT(onTimeout())) which fires the timer only once and doesn't require declaring a variable.

P.s.s. A Qt convention is to start variable and method names with lowercase letters. Uppercase is for types, so they can be easily distinguished from variables.

[hungcotac]

Yup. So we can't pass argument. But can you tell me why Qt make this limit ? for what ?

[Zmey]

I guess signals are designed to be similar to function declarations.

The actual data is passed when emitting a signal (similar to calling a function). The main difference is that a function can have only one implementation, but signal can be attached to multiple slots and these connections can be reconfigured at runtime.