Is it possible to create a pointer to the main window?

[ghkraju]

Hi I have a Qt Application and ROS Action Server which takes in requests and invoke some features of my application like displaying dialog windows etc,.

My Main method is something like this:

int main(int argc, char *argv[]) {
qInstallMessageHandler(myMessageOutput);

if( !ros::isInitialized() )
  {
    ros::init( argc, argv, "APS");//, ros::init_options::AnonymousName );
    ros::param::set("/use_gui", true);
    
  }
QApplication a(argc, argv);
w = new MainWindow;
w->show();

GUIActionServer as_(ros::this_node::getName(), w);// Here I start my action server based on the reqests i have to invoke some functionalites in my Main window
    
int result = a.exec();

delete w;
w=NULL;

return result;

}

GUIActionServer.h is as follows:

#ifndef GUIACTIONSERVER_H
#define GUIACTIONSERVER_H
#include <ros/ros.h>
#include <actionlib/server/simple_action_server.h>
#include <aps_msgs/MoveArmAction.h>
#include <moveit_msgs/MoveItErrorCodes.h>
#include <configdialog.h>
#include <QDebug>
#include "mainwindow.h"

#include <QObject>

class GUIActionServer : public QObject
{
    Q_OBJECT

public:
    GUIActionServer(std::string name, MainWindow* w);
    ~GUIActionServer();
    void executeCB(const aps_msgs::MoveArmGoalConstPtr &goal);

protected:

  ros::NodeHandle nh_;
  // NodeHandle instance must be created before this line. Otherwise strange error may occur.
  actionlib::SimpleActionServer<aps_msgs::MoveArmAction> as_; 
  std::string action_name_;
  // create messages that are used to published feedback/result
  aps_msgs::MoveArmFeedback feedback_;
  aps_msgs::MoveArmResult result_;
  MainWindow* sw;
};

#endif // GUIACTIONSERVER_H

GUIActionServer.cpp is as follows:

#include "guiactionserver.h"

GUIActionServer::GUIActionServer(std::string name, MainWindow* w) :
    as_(nh_, name, boost::bind(&GUIActionServer::executeCB, this, _1), false),
    action_name_(name)
  {
    as_.start();
    sw = w;
  }

  GUIActionServer::~GUIActionServer(){};

  void GUIActionServer::executeCB(const aps_msgs::MoveArmGoalConstPtr &goal)
  {
    // helper variables
    ros::Rate r(1);
    bool success = true;

    feedback_.state = "In Execute Callback method";

    std::cout << goal->exec_path.at(0).position.x << std::endl;

    as_.publishFeedback(feedback_);
    r.sleep();

    if(sw){
        sw->testDialog();
    }
    
    sw = NULL;

    success = true;

    if(success)
    {
      result_.error_code.val = 1;
      ROS_INFO("%s: Succeeded", action_name_.c_str());
      // set the action state to succeeded
      as_.setSucceeded(result_);
    }
  }

When I am using the above code application is not stable and got the following error

QObject::connect: Cannot queue arguments of type 'QTextBlock'
(Make sure 'QTextBlock' is registered using qRegisterMetaType().)
QObject::connect: Cannot queue arguments of type 'QTextCursor'
(Make sure 'QTextCursor' is registered using qRegisterMetaType().)
Segmentation fault (core dumped)

Any ideas will be much appreciated. Thanks in advance

[SGaist]

Hi,

Looks like you are already doing something fishy with some signals and slots. Can you show the code where you establish these connections ?

[ghkraju]

GUIActionServer as_(ros::this_node::getName(), w);// Where i creates my obj to Action Server and pass the mainwindow 'w'.

// Assigns to another pointer in GUIActionServer Mainwindow* sw;
sw = w;

// Calls the testDialog method in GUIActionServer::executeCB function which popsup Dialog in mainwindow
if(sw){
sw->testDialog();
}

Hope this looks simple rather than going through the whole code...

[SGaist]

Except your error has nothing to do with the code you posted and more likely with the rest your didn't post.

Like the error says, you are trying to use a type that is not known to the signal and slots system so you likely did some connect calls somewhere in your code. That's the part that must be checked.

[ghkraju]

If I remove my GUIActionServer then the application works fine. This error popsup only when i include this GUIActionServer thingy. I suspect there might be some wrong thing in the way i work with threads and pointers.

I have one General question MainWindow has its own thread and GUIActionServer will also up and running. Can i invoke the main thread whenever my Action Server wants to talk to it?

[SGaist]

No, you cannot modify directly GUI elements from another thread. You should use signals and slots for that.

But still, the connect error should be investigated.

[ghkraju]

In that case, I think this might be causing the error:

void MainWindow::testDialog(){
    ConfigDialog cond;
    qInfo() << "From Action Server obj is created";
    cond.setMode("View");
    qInfo() << "Mode is " << cond.mode.c_str();
    cond.updateConfigDialog();
    cond.setModal(false);
    cond.exec();
}

I am creating a new dialog whenever i receive a request from the action server. Mightbe it is failing here to connect Qobjects because this is a pointer to mainwindow. Am I correct?

[SGaist]

No you're not.

Connection error like that have nothing to do with the fact that you are using a pointer for your MainWindow.

Again, do you have any connect statement somewhere in your code ?

[ghkraju]

I have these connections which are present in the ConfigDialog.ui

<connections>
  <connection>
   <sender>buttonBox</sender>
   <signal>accepted()</signal>
   <receiver>ConfigDialog</receiver>
   <slot>accept()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>248</x>
     <y>254</y>
    </hint>
    <hint type="destinationlabel">
     <x>157</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
  <connection>
   <sender>buttonBox</sender>
   <signal>rejected()</signal>
   <receiver>ConfigDialog</receiver>
   <slot>reject()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>316</x>
     <y>260</y>
    </hint>
    <hint type="destinationlabel">
     <x>286</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
 </connections>

Other than these i haven't defined any custom connections. I have searched my code but I am unable to find QTextBlock and QTextCursor defined

[ghkraju]

I got it..... I have made a mistake I was calling the testDialog using normal method instead of signals and slots. Now i have connected as follows:

GUIActionServer::GUIActionServer(std::string name, MainWindow* w) :
    as_(nh_, name, boost::bind(&GUIActionServer::executeCB, this, _1), false),
    action_name_(name)
  {
    as_.start();
    sw = w;
// Connecting using signals and slots here 
// ActionInvoked is a signal in GUIActionServer and testDialog is a public slot in MainWindow
    QObject::connect(this, &GUIActionServer::actionInvoked, w, &MainWindow::testDialog);
  }

  GUIActionServer::~GUIActionServer(){};

  void GUIActionServer::executeCB(const aps_msgs::MoveArmGoalConstPtr &goal)
  {
    // helper variables
    ros::Rate r(1);
    bool success = true;

    feedback_.state = "In Execute Callback method";

    std::cout << goal->exec_path.at(0).position.x << std::endl;

    as_.publishFeedback(feedback_);
    r.sleep();
// If main window is opened then I will call the signal.
    if(sw){
        actionInvoked();
    }
    
    sw = NULL;

    success = true;

    if(success)
    {
      result_.error_code.val = 1;
      ROS_INFO("%s: Succeeded", action_name_.c_str());
      // set the action state to succeeded
      as_.setSucceeded(result_);
    }
  }

The previous issue is related to threading i guess.... Now I am not receiving any error the code works fine. Thank you for your support @SGaist