Calculator Form Example

CalculatorForm Class Implementation

The constructor simply calls the base class's constructor and sets up the form's user interface.

 CalculatorForm::CalculatorForm(QWidget *parent)
     : QWidget(parent)
 {
     ui.setupUi(this);
 }

The user interface is set up with the setupUI() function. We pass this as the argument to this function to use the CalculatorForm widget itself as the container for the user interface.

To automatically connect signals from the spin boxes defined in the user interface, we use the naming convention that indicates which widgets and their signals in the user interface should be connected to each slot. The first slot is called whenever the spin box called "inputSpinBox1" in the user interface emits the valueChanged() signal:

 void CalculatorForm::on_inputSpinBox1_valueChanged(int value)
 {
     ui.outputWidget->setText(QString::number(value + ui.inputSpinBox2->value()));
 }

When this occurs, we use the value supplied by the signal to update the output label by setting its new text directly. We access the output label and the other spin box via the class's private ui variable.

The second slot is called whenever the second spin box, called "inputSpinBox2", emits the valueChanged() signal:

 void CalculatorForm::on_inputSpinBox2_valueChanged(int value)
 {
     ui.outputWidget->setText(QString::number(value + ui.inputSpinBox1->value()));
 }

In this case, the value from the first spin box is read and combined with the value supplied by the signal. Again, the output label is updated directly via the ui variable.