Simple sound (.wav) playing application in QT (C++) - c++

Question

I am new to Qt and was trying to write a simple qt class that can plan a wav file.
After some reading and looking around I wrote the class and the code is as below. Questions follow after code
#include <QtGui/QApplication>
#include "playsound.h"
#include <iostream>
using namespace std;
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
playSound w;
int ch = 2;
int ready = 1;
cout<<"ready"<<ready<<endl;
// w.show();
w.playwav(ch);
return a.exec();
}
Source code for playsound.cpp
#include "playsound.h"
playSound::playSound(QWidget *parent): QWidget(parent) {}
playSound::~playSound() {}
void playSound::playwav(int ch)
{
switch (ch)
{
case 1: {QSound::play("/home/alok/qtworkspace/sounds/abc.wav"); break;}
case 2: {QSound::play("/home/alok/qtworkspace/sounds/xyz.wav"); break;}
case 3: {QSound::play("/home/alok/qtworkspace/sounds/abc.wav"); break;}
case 4: {QSound::play("/home/alok/qtworkspace/sounds/aaa.wav"); break;}
case 5: {QSound::play("/home/alok/qtworkspace/sounds/nnn.wav"); break;}
}
}
Problems and questions:
1) I want to close the application once the sound is played.As of now it says program running and I have to forcefully close it using the red button in the "Application Output" area in Qt creator. I tried using close() from Qwidget and quit() from QApplication but probably I am doing it wrong. How to go abt this?
2) Can there be a simpler implementation for this functionality? You know something that does not involve event loops. I was trying to do it in old school C++ style where I call a function when I need to play a sound and be done with it but could not get it done. Suggestions most welcome on this one.
Thanks

Answer 1

I can offer an answer using PyQt4 (since I'm a python coder), but the idea is the same.
1) QSound is a very basic interface for playing sounds. It doesn't have any useful signals (though I think it really should). In order to know when the QSound is complete, you have to keep checking its isFinished() method. You could either do this in a loop in your main thread, or get more advanced and create a QThread which will play your sound, go into the loop, and then emit its own custom signal when its complete. The QThread is preferred because you should never block your main thread. You would then be able to connect this custom soundIsFinished() SIGNAL to say the close() SLOT of your widget, or any other handler.
If you want more advanced options, you can use the phonon module, which does have all of these various signals built in. Its a litte more annoying to set up, but then you won't need a QThread.
2) Event loops are the core concept of how Qt functions. Your main application always enters an event loop so that widgets can post their events and have them processed. You could technically use Qt without an event loop, but then its really pointless because you are just fighting against the framework and losing everything that its capable of.

Answer 2

To exit from an application, you have to close the top level widget (if you're App has the property verbosely named quitOnLastWindowClosed set to true, but this is default so you don't have to worry with it) or emit a quit signal to the QCoreApplication you've created.
In the example below, I've taken the easy way: emit a close signal.
As stated by jdi, it would be better to create a Thread, but I've understood that you're only learning Qt and wrote this as an example, so busy waiting for isFinished is good enough. Below an example of how it should go:
#include "playsound.h"
playSound::playSound(QWidget *parent): QWidget(parent) {}
playSound::~playSound() {}
void playSound::playwav(int ch)
{
QSound *player = 0; // Creates an object so that you can call player.isFinished()
// the isFinished function is not static.
switch (ch)
{
case 1: {player = new QSound("/home/alok/qtworkspace/sounds/abc.wav"); break;}
// other cases
}
if(!player)
this->close();
while(!player->isFinished()); // waits until the player has finished playing
delete player;
this->close(); // closes this widget, and
// as this Widget has no parent, i.e. it's the "top-level" widget,
// it'll close the app.
}
edit: Shame on me for not reading the docs how I should have. QSound does not have a default constructor, I've edited the code.
A few notes: as this is only a test for you to learn how to use Qt, I've created a pointer to QSound and deleted it afterward. This is not a good approach, you should not play with pointers as I did there, a much better solution would be only instantiating the object you would use. Having to delete things manually is not good, and it's really better to rely on the good ol' stack for that.