Qt event emit inside thread not working properly

sujith D

void loaddepth::run(){
   
 
    QString file_name=this->filename;
    int day=this->day_no;
    int depth=this->deepth_no;
 
    QFile *file=new QFile(file_name);
    QTextStream in(file);
    file->open(QIODevice::ReadOnly | QIODevice::Text);
    const auto size = file->size();

     QStringList strList;
     bool flag=false;


        QStringList list;
        int line=0;
        int day_count=0;

        while(!in.atEnd()&&day_count<=day)
        {
            QString str=in.readLine().simplified();
            QStringList list=str.split(' ');

            if(list.count()==3){

                if(flag){
                    **emit readStatusChanged(this->file_no,list[0],list[1],list[2].toDouble());**

                }
 

 
            } else if(list.count()==1){

                if(list[0].toInt()!=depth&&flag==true){
                    qDebug()<<"b4 senting";
           }

                if(list[0].toInt()==depth){

                        flag=true;

                }

            }

   line++;
        }


}
 ******************************
connect(fileData1,SIGNAL(readStatusChanged(int,QString,QString,double)),this,SLOT(onReadStatusChanged(int,QString,QString,double)));

**event emits is not triggering inside the thread loop.**

Christian Ehrlicher

Did you check if the connect is successful and if you really emit the signal? Please show us where you connect the signal/slot connection.

sujith D

@Christian-Ehrlicher ya emit works only outside while loop. it doesn't work inside the loop.

connect(fileData1,SIGNAL(readStatusChanged(int,QString,QString,double)),this,SLOT(onReadStatusChanged(int,QString,QString,double)));

Christian Ehrlicher

@sujith-D said in Qt event emit inside thread not working properly:

ya emit works only outside while loop. it doesn't work inside the loop.

Again: how did you check that the signal is emitted? Did you added a breakpoint? Or a debug output?

And you still did not check the return value of connect() and did not show us the code around the connect on how you instantiate the class etc.

sujith D

@Christian-Ehrlicher

I do qDebug(), and its output.

Christian Ehrlicher

@sujith-D said in Qt event emit inside thread not working properly:

I do qDebug(), and its output.

Again: please show us more code, best a minimal example so we can try to reproduce it.

sujith D

@Christian-Ehrlicher
Calling thread from module2. Declared signals and slots in corresponding header files.
I don't know why the same event not working inside the loop during the file read.

Module2::Module2(QWidget *parent) :
    QWidget(parent),
    rect(0),
    ui(new Ui::Module2),
    scaleFactor(1),
    mapDim(1500)
{
    fileData1=new loaddepth(this);
 fileData1->filename=QCoreApplication::applicationDirPath()+"/../project3DUnderWater/0.txt";
fileData1->deepth_no=1;
connect(fileData1,SIGNAL(readStatusChanged(int,QString,QString,double)),this,SLOT(onReadStatusChanged(int,QString,QString,double)));
    connect(fileData1,SIGNAL(ReadFileCompleted(int,QJsonObject)),this,SLOT(onReadFileCompleted(int,QJsonObject)));
fileData1->start();

}

void Module2::onReadStatusChanged(int file_no,QString y,QString x,double z ){
    qDebug()<<"file_no"<<file_no;

}

void Module2::onReadFileCompleted(int file_no,QJsonObject json){

 qDebug() <<json;

}

module2 header file

#include<QProgressDialog>
namespace Ui {
class Module2;
}

class Module2 : public QWidget
{
    Q_OBJECT

public:
    explicit Module2(QWidget *parent = nullptr);
    ~Module2();
 
    loaddepth *fileData1;

private slots:
    void onReadStatusChanged(int,QString,QString,double);
    void onReadFileCompleted(int,QJsonObject);
};

Thread header file

#include<QtCore>
class loaddepth:public QThread
{
   Q_OBJECT
public:
    loaddepth(QObject *parent=0);
    void run() override;
    bool stop;
   QString  filename; int day_no;
   int deepth_no;
      QJsonObject obj;
int file_no;

signals:

        void readStatusChanged(int,QString,QString,double);
        void ReadFileCompleted(int,QJsonObject);

 
};

Christian Ehrlicher

This is working fine for me:

#include <QtCore>

class MyThread : public QThread
{
  Q_OBJECT
public:
  using QThread::QThread;

  void run() override
  {
    while (true) {
      emit emitSignal();
      QThread::sleep(2);
    }
  }

Q_SIGNALS:
  void emitSignal();
};

class MyObject : public QObject
{
  Q_OBJECT
public:
  MyObject(QObject *parent = nullptr)
    : QObject(parent)
  {
    MyThread *mt = new MyThread(this);
    connect(mt, &MyThread::emitSignal, this, &MyObject::mySlot);
    mt->start();
  }
private Q_SLOTS:
  void mySlot() { qDebug() << "Got signal!"; }
};

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    MyObject obj;
    return app.exec();
}

#include "main.moc"

Btw: no need to create (and leak) a QFile object on the heap.