QT client doesn't download file when action is placed on button - c++

Question

Code in main.cpp
Client c;
c.start("ip-address", port, "final folder/file");
It works and client downloads file I need.
But if I place same code in mainwindow.cpp on button click action
void MainWindow::on_btn_connect_clicked()
{
Client c;
c.start("ip-address", port, "final folder/file");
}
it doesn't work. Why is that? I'm newbie at Qt and network coding. Some source code
void Client::start(QString address, qint16 port, QString file)
{
qDebug() << "client started";
QHostAddress addr(address);
filename = file;
client->connectToHost(addr, port);
qDebug() << client->socketDescriptor();
}
I have readyRead() but programm doesn't get there.
Client::Client(QObject *parent) :
QObject(parent)
{
client = new QTcpSocket(this);
client->abort();
connect(client, SIGNAL(readyRead()), this, SLOT(ReadData()));
connect(client, SIGNAL(disconnected()), this, SLOT(Completed()));
}

Answer 1

Did you connect the buttons clicked signal to the on_btn_connect slot?

Answer 2

When you create the Client like this:
void MainWindow::on_btn_connect_clicked()
{
Client c;
c.start("ip-address", port, "final folder/file");
}
The client object is created, start is called, then it is immediately destroyed one execution leaves the on_btn_conenct_clicked() function. This will never work unless the "start" function is completely finished doing whatever you want it to do by the time you leave it, which does not appear to be the case by the code you posted.
For this to work, you'd have to make client a member of the MainWindow class so it sticks around after the slot is called. Another alternative would be to make it a pointer, create it in the on_btn_connect_clicked() slot, then connect whatever signal gets emitted when its all done with its work to its own deleteLater slot. Like so:
void MainWindow::on_btn_connect_clicked()
{
Client* c = new Client(this);
connect(c, &Client::downloadComplete, c, &Client::deleteLater);
c->start("ip-address", port, "final folder/file");
}
The downloadComplete signal is something that you have to make sure you emit yourself whenever the action you are trying to accomplish is completed, otherwise you'll have a memory leak and the client object will not get deleted until the entire MainWindow is deleted.