Dynamically linking signals and slots for buttons

[chandru@080]

I have created some dynamic buttons through XML in my code. I want to know how do i connect slots to this dynamically created buttons?

[high_flyer]

Here you go:
http://doc.trolltech.com/4.7/signalsandslots.html

[chandru@080]

Thanks for the response.. i dint frame my question well.. i have some more queries on the same subject
I have created 5 buttons from XML. and that is displayed on the screen. i want to know how to do the following things

1. If i click on dynamically created button how can i identify which button i have clicked?
2. How do i get the button name when i click on the button?
3. How do i set an event for the button

Any respone will be of great help

[FelixB]

inside a slot, you can get the sender by "QPushButton* button = qobject_cast<QPushButton*>sender()". If the cast fails, button is NULL.

Please show us the code how you create the buttons.

[chandru@080]

I find the number of child nodes and then get the count using the QDomNodeList and then use a for loop connect the signal with the slots like this,

connect(Button1[i],SIGNAL(clicked()),this,SLOT(Display()));

connect(Button1[i],SIGNAL(clicked()),this,SLOT(Display()));

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I need to know which is the button that is clicked in the Display button and there is where i am stuck

This is how i create my buttons.

Button1[i] = new QPushButton( this);
    Button1[i]->setGeometry(QRect(x ,y,button_width,button_height));
    Button1[i]->setText(QApplication::translate("Widget", text.toStdString().c_str(), 0, QApplication::UnicodeUTF8));
    Button1[i]->show();

Button1[i] = new QPushButton( this);
    Button1[i]->setGeometry(QRect(x ,y,button_width,button_height));
    Button1[i]->setText(QApplication::translate("Widget", text.toStdString().c_str(), 0, QApplication::UnicodeUTF8));
    Button1[i]->show();

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[high_flyer]

I need to know which is the button that is clicked in the Display button and there is where i am stuck

FlixB already answered that - you can use the sender() method to compare against your buttons.

[chandru@080]

Wiseguy.. its true that FixB told me how to go about it.. but i am completely new to QT and i am doing and things are going over my head. so its taking me time to figure out how to use the sender function and other API's

[FelixB]

Wiseguy.. its true that FixB told me how to go about it.. but i am completely new to QT and i am doing and things are going over my head. so its taking me time to figure out how to use the sender function and other API's

it's not a problem being a beginner. i started with qt some months ago and a lot of things were confusing to me. BUT: what is your problem now? put the line i posted above in your "Display()" method and you have access to the clicked button.

this thread is something like:
A: can someone help me adding 2 and 3?
B: use "plus"-operator
A: thank you, but i need to know how to add the values
C: use the solution posted by A
B: sorry, I'm new. I don't know how to use "plus"

[chandru@080]

Well Said... There is no problem now.. I got it done. thanks a lot. I completely agree with the steps that you mentioned.. i was going round and round and later found that it was such a simple thing that can be done in no time... well i guess i need to bang my head somewhere for wasting so much of time.

Felix thanks a ton for the response.

[minirop]

to identify a button, use the QSignalMapper.
short example :

QSignalMapper * mapper = new QSignalMapper(this);
QDomElement child = elem.firstChildElement("choice");
while(!child.isNull())
{
	QPushButton * button = new QPushButton(child.text());
	connect(button, SIGNAL(clicked()), &mapper, SLOT(map()));
	mapper.setMapping(button, child.attribute("value"));
	vLayout->addWidget(button);
 
	child = child.nextSiblingElement("choice");
}
connect(mapper, SIGNAL(mapped(const QString &)), this, SLOT(onbuttonClicked(const QString &)));

QSignalMapper * mapper = new QSignalMapper(this);
QDomElement child = elem.firstChildElement("choice");
while(!child.isNull())
{
	QPushButton * button = new QPushButton(child.text());
	connect(button, SIGNAL(clicked()), &mapper, SLOT(map()));
	mapper.setMapping(button, child.attribute("value"));
	vLayout->addWidget(button);
	
	child = child.nextSiblingElement("choice");
}
connect(mapper, SIGNAL(mapped(const QString &)), this, SLOT(onbuttonClicked(const QString &)));

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the slot :

void Mainwindow::onbuttonClicked(const QString& value)
{
	// value is here to identify the button
}

void Mainwindow::onbuttonClicked(const QString& value)
{
	// value is here to identify the button
}

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And I use it with this kind of XML :

<choices name="image">
	<choice value="animated">Show an animated image</choice>
	<choice value="not">Show a picture</choice>
	<choice value="nothing">Pass</choice>
</choices>

<choices name="image">
	<choice value="animated">Show an animated image</choice>
	<choice value="not">Show a picture</choice>
	<choice value="nothing">Pass</choice>
</choices>

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so when I click on "Show a picture", the slot "onbuttonClicked" is called with the value "not".

[pradhan]

Hi ,

As felix said i have used "QPushButton* button = qobject_cast<QPushButton*>sender()" in my push button click slot. But when i compile i get the following error:

error: cannot resolve overloaded function 'qobject_cast' based on conversion to type 'QPushButton*'

Kindly help.

[high_flyer]

It should be:

QPushButton* button = qobject_cast<QPushButton*>(sender());

QPushButton* button = qobject_cast<QPushButton*>(sender());

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[gab74]

I try to use the code below :

while(!child.isNull())
{
QPushButton * button = new QPushButton(child.text());
connect(button, SIGNAL(clicked()), &mapper, SLOT(map()));
mapper.setMapping(button, child.attribute("value"));
vLayout->addWidget(button);
 
child = child.nextSiblingElement("choice");
}
connect(mapper, SIGNAL(mapped(const QString &)), this, SLOT(onbuttonClicked(const QString &)));

while(!child.isNull())
{
QPushButton * button = new QPushButton(child.text());
connect(button, SIGNAL(clicked()), &mapper, SLOT(map()));
mapper.setMapping(button, child.attribute("value"));
vLayout->addWidget(button);
 
child = child.nextSiblingElement("choice");
}
connect(mapper, SIGNAL(mapped(const QString &)), this, SLOT(onbuttonClicked(const QString &)));

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in the SLOT I receive correctly the value passed

void Mainwindow::onbuttonClicked(const QString& value)
    {
    // value is here to identify the button
 
	QPushButton* button = qobject_cast<QPushButton*>(sender());
 
    }

void Mainwindow::onbuttonClicked(const QString& value)
    {
    // value is here to identify the button

	QPushButton* button = qobject_cast<QPushButton*>(sender());

    }

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the button object is always NULL, why this ?
I want to retrieve button name but the sender is always NULL..

[anda_skoa]

the button object is always NULL, why this ?

The sender of the signal is the QSIgnalMapper. It cannot be casted to QPushButton, so the qobject_cast returns a null pointer.

I want to retrieve button name but the sender is always NULL..

If you mean button pointer, see QSignalMapper::mapping()

Cheers,
_