Why does my label disappear on button click? - qt

Question

I am brand new to Qt development and am trying to make a simple "Hello, World" with a toggle-button. I have something like this:
with the corresponding code:
void MainWindow::on_pushButton_toggled(bool checked)
{
if(checked) {
ui->label->setText("Hello, World!");
} else {
ui->label->setText("");
}
}
My goal is to change the label's text either from blank to "Hello, World!" or vice versa on a button click.
Currently the label only stays blank. Earlier the default text was "TextLabel", and on a button-click, it would change from "TextLabel" to blank, which is almost correct.
I've tried different options like on_pushButton_clicked, but to no avail.
I know the solution is a simple one -- can anyone point me in a good direction?

Answer 1

Why don't you do it like this?
void MainWindow::on_pushButton_toggled(bool checked)
{
ui->label->setText(ui->label->text().isEmpty() ? "Hello, World!" : "");
}

Answer 2

You need to declare your callback method as below :
class MainWindow : public QMainWindow
{
Q_OBJECT
bool checked;
QPushButton *my_button;
private slots:
void handleButton();
};
Then in your Constructor you need to connect Signal and Slot as below :
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
checked = 0;
connect(my_button, SIGNAL (released()), this, SLOT (on_pushButton_toggled()));
}
Your call back method will be like this. You can toggle your flag in this method as every time you click this SLOT will be called.
void MainWindow::on_pushButton_toggled()
{
checked = ~checked;
if(checked) {
ui->label->setText("Hello, World!");
} else {
ui->label->setText("");
}
}
I hope this will work out for you.

Answer 3

QPushButton is not checkable by default; you need to call QAbstractButton::setCheckable(true); before you can really use the QAbstractButton::toggled signal in any meaningful way. What happens in your code is that your slot is being called with the value false passed every single time because the button simply isn't checkable.