CODEWITHSUNDEEP
qtqsignalmapperqt-slot
Fatih Arslan
Fatih Arslan

Reputation: 1114

Passing an argument to a slot

I want to override mouseReleaseEvent with a bunch of QActions and QMenus...

connect(action1, SIGNAL(triggered()), this, SLOT(onStepIncreased()));

connect(action5, SIGNAL(triggered()), this, SLOT(onStepIncreased()));

connect(action10, SIGNAL(triggered()), this, SLOT(onStepIncreased()));

connect(action25, SIGNAL(triggered()), this, SLOT(onStepIncreased()));

connect(action50, SIGNAL(triggered()), this, SLOT(onStepIncreased()));

So I want to pass an argument to the slot onStepIncreased (as you can imagine they are 1,5,10,25,50). Do you know how I can do it?

Upvotes: 100

Views: 99126

Answers (6)

user10609288
user10609288

Reputation:

You can use std::bind This is a functional object adapter that allows functional objects to be adaptee to a given number of parameters.

For example, you create your own chat server. That contains two classes: ChatServer and ServerWorker.

ChatServer is QTcpServer class and ServerWorker is QTcpSocket ( manage the socket on the server side).

Signals in ServerWorker header:

void error();

In your ChatServer header you define these private slots:

void userError(ServerWorker *sender);

In cpp file you create these object and in incomingConnection method that run after socket connect, you connect slots and signals using std::bind:

void ChatServer::incomingConnection(qintptr socketDescriptor)
{
    //some code
    connect(worker, &ServerWorker::error, this, std::bind(&ChatServer::userError, this, worker));
}

std::bind creates a functor with some fixed arguments. For example connect(worker, &ServerWorker::error, this, std::bind(&ChatServer::userError, this, worker)); will result in this->userError(worker); to be called every time the worker emits the error signal.

userErrorslot is executed every time a socket connected to a client encounters an error. It has signature:

void ChatServer::userError(ServerWorker *sender)
{
    //some code
}

Example

Upvotes: 4

Jaziri Rami
Jaziri Rami

Reputation: 317

QVector<QAction*> W(100);
 W[1]= action1;
 W[5]= action5;
 W[10]= action10;
 W[25]= action25;
 W[50]= action50;

for (int i=0; i<100; ++i)
{
  QSignalMapper* signalmapper = new QSignalMapper();
  connect (W[i], SIGNAL(triggered()), signalmapper, SLOT(map())) ;
  signalmapper ->setMapping (W[i], i);
  connect (signalmapper , SIGNAL(mapped(int)), this, SLOT(onStepIncreased(int)));
}

Upvotes: 0

TonyK
TonyK

Reputation: 17114

Use QSignalMapper. Like this:

QSignalMapper* signalMapper = new QSignalMapper (this) ;
connect (action1, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action5, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action10, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action25, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action50, SIGNAL(triggered()), signalMapper, SLOT(map())) ;

signalMapper -> setMapping (action1, 1) ;
signalMapper -> setMapping (action5, 5) ;
signalMapper -> setMapping (action10, 10) ;
signalMapper -> setMapping (action25, 25) ;
signalMapper -> setMapping (action50, 50) ;

connect (signalMapper, SIGNAL(mapped(int)), this, SLOT(onStepIncreased(int))) ;

Upvotes: 130

Kuba hasn&#39;t forgotten Monica
Kuba hasn&#39;t forgotten Monica

Reputation: 98425

With Qt 5 and a C++11 compiler, the idiomatic way to do such things is to give a functor to connect:

connect(action1,  &QAction::triggered, this, [this]{ onStepIncreased(1); });
connect(action5,  &QAction::triggered, this, [this]{ onStepIncreased(5); });
connect(action10, &QAction::triggered, this, [this]{ onStepIncreased(10); });
connect(action25, &QAction::triggered, this, [this]{ onStepIncreased(25); });
connect(action50, &QAction::triggered, this, [this]{ onStepIncreased(50); });

The third argument to connect is nominally optional. It is used to set up the thread context in which the functor will execute. It is always necessary when the functor uses a QObject instance. If the functor uses multiple QObject instances, they should have some common parent that manages their lifetime and the functor should refer to that parent, or it should be ensured that the objects will outlive the functor.

On Windows, this works in MSVC2012 & newer.

Upvotes: 153

king_nak
king_nak

Reputation: 11513

The QObject::sender() function returns a pointer to the object that has signaled to the slot. You could use this to find out which action was triggered

Upvotes: 14

Kurt Pattyn
Kurt Pattyn

Reputation: 2788

Maybe you can subclass QAction with an m_increase member variable.
Connect the triggered() signal to a slot on your new QAction subclass and emit a new signal (e.g. triggered(int number)) with the correct parameter.
e.g. 

class MyAction:public QAction  
{  
public:  
    MyAction(int increase, ...)  
        :QAction(...), m_increase(increase)
    {  
        connect(this, SIGNAL(triggered()), this, SLOT(onTriggered()));  
    }  
protected Q_SLOTS:  
    void onTriggered()  
    {  
        emit triggered(m_increase);  
    }  

Q_SIGNALS:
    void triggered(int increase);   

private:  
    int m_increase;  
};

Upvotes: 1

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