QT 5.4.1 sending value in the form1 mainwidow to form2

Question

I am a beginner in QT. I would like to send the value back into the LineEdit mainwindow to GraphicsWidget window to make calculations.

mainwindow.ccp

int value=ui->lineEdit->text().toInt();

GraphicsWidget.ccp

qDebug()<<value;

Answer 1

1. You can use Qt signal and slots. For more information refer the documentation here

2. The implementation for your case will be something like this in

   MainWindow.cpp constructor

   GraphicsWidget _graphicsWidget;
   connect(this,SIGNAL(sendLineEditValue(int)), &_graphicsWidget,SLOT(receiveLineEditValue(int)));
   

   mainwindow.h

   signals:
   void sendLineEditValue(int value);
   

   mainwindow.cpp

   void MainWindow::decideToSend(){
   int value=ui->lineEdit->text().toInt();
   emit sendLineEditValue(value);
    }
   

   graphicswidget.h

   public slots:
   void receiveLineEditValue(int value);
   

   graphicsgidget.ccp

   void GraphicsWidget::receiveLineEditValue(int value){
   qDebug()<<value;
   }
   

3. The idea is when ever you emit a signal, the connected slot will be called.

4. An implemetation without signal slot is to directly call the GraphicsWidget::receiveLineEditValue(int value) from the MainWindow

Answer 2

You can use SIGNAL&SLOT for that purpose, however if you are new and you dont know anything about SIGNAL&SLOT, you can just pass value to another function.

graphicswidget.h

public:
void receiveLineEditValue(int value);

mainwindow.cpp

GraphicsWidget* _graphicsWidget;
_graphicsWidget->receiveLineEditValue(value);