Implementing QTimer to execute a function for a given time - c++

Question

I have a function that should send data to a raspberry pi for a given period of time depending on the parameter.
//headerfiles
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
QUdpSocket udpSocket;
// movement Timer
QTimer* movementTimer;
private slots:
void sendDatagram(); // Sends to the RaspberryPi
void processFrameAndUpdateGUI();
void turnLeft(double time);
void turnRight(double time);
void goStraight(double time);
void MovRobot();
};
// MainWindow.cpp
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
movementTimer = new QTimer(this);
//send datagram sends data to tehe PI.
connect(movementTimer, SIGNAL(timeout()), this, SLOT(sendDatagram()));
MovRobot(); // MovRobot() function
}
// controls robot to turn left for specified time
void TurnLeft(double time)
{
s = 1; // sets the value to be sent to the PI.
movementTimer->setInterval(time);
movementTimer->setSingleShot(true);
movementTimer->start();
}
//sendDatagram() slot
void MainWindow::sendDatagram() {
QString datagramOutput = "start," +
QString::number(w) + ',' + QString::number(a) + ',' +
QString::number(s) + ',' + QString::number(d) + ',' +
QString::number(ui->motorSpeedSlider->value()) + ',' +
QString::number(dispenserSignal);
datagramOutput += ",end";
QByteArray datagram;
QDataStream out(&datagram,QIODevice::WriteOnly);
out << datagramOutput;
udpSocket.writeDatagram(datagram,QHostAddress("192.168.0.104"),12345);
}
//MovRobot Function;
void MainWindow :: MovRobot() {
if (ui->pushButton_3->isChecked()) {
MapArea(); // This function maps the area....
// final_plan is a vector<Point2i> that stores positions on the map for
// the robot to move to
for (int i = 0; i < final_plan.size(); i++) {
for (int j = final_plan.size() - 1; j>=0; j--) {
do {
Mat src;
bool bsuccess = cap.read(src);
if (!bsuccess) {
ui->label_34->setText("Status: Can't read frame.");
ui->pushButton_3->setChecked(0);
}
GetRobotPosition(src);
// AngleToGoal calculates the angle of the robot relative
// to the final goal.
double tempAngle = AngletoGoal(final_plan[i][j]);
if (tempAngle>=0) {
turnLeft(TimeToTurn(tempAngle));
}
else {
turnRight(TimeToTurn(tempAngle));
}
double tempDistance = DistancetoGoal(final_plan[i][j]);
goStraight(tempDistance);
} while (DistancetoGoal(final_plan[i][j])<20);
}
}
}
}
The timer should only send the data over to the PI for the duration it in time sendDatagram is the function that sends the data over to the Pi. Is there anything I'm missing here. The timer doesn't start inside the TurnLeft() function and doesn't run at all. Am I going about this wrong?
EDIT: 13/03/2016:
My apologies for the late reply. I've been quite sick the past few days. I've added the relevant parts of the code. MovRobot() is the main function responsible for the movement and this is called in the constructor for MainWindow. I have debugged and stepped through the program and yes, TurnLeft() is called. However, the sendDatagram() slot doesn't actually send anything in the function. To confirm sendDatagram() was actually working, I used another timer to continuously send information to the PI on the robot to control the arm.
// Header File
QTimer* tmrTimer;
private slot:
void processFrameAndUpdateGUI();
// MainWindow Constructor:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
connect(tmrTimer, SIGNAL(timeout()), this, SLOT(processFrameAndUpdateGUI()));
tmrTimer->start(10);
}
void MainWindow::processFrameAndUpdateGUI() {
sendDatagram();
}
The sendDatagram() slot is pretty much the same with the exception of me changing what values are being sent to the PI and this seems to work perfectly.
However, my original problem is, I would like to send the data to the robot with for a specified amount of time as that makes the robot turn x degrees. This is why I've made movementTimer() single shot.
Stepping through my program, I know this line is called within my TurnLeft function.
movementTimer->start();
but the sendDatagram() slot itself doesn't actually send anything to the PI.

Answer 1

Based on your code. The program never called TurnLeft(). So the timer never started. It will be better to start the timer in constrator instead.

Answer 2

timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(MySlot()));
timer->start(1000);
I would try setting the timer to start in the constructor.