Line Edits Example▲

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The example consists of a single Window class, containing a selection of line edits with different input constraints and display properties that can be changed by selecting items from comboboxes. Presenting these together helps developers choose suitable properties to use with line edits, and makes it easy to compare the effects of each validator on user input.

Window Class Definition▲

The Window class inherits QWidget and contains a constructor and several slots:

 
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class Window : public QWidget
{
    Q_OBJECT

public:
    Window();

public slots:
    void echoChanged(int);
    void validatorChanged(int);
    void alignmentChanged(int);
    void inputMaskChanged(int);
    void accessChanged(int);

private:
    QLineEdit *echoLineEdit;
    QLineEdit *validatorLineEdit;
    QLineEdit *alignmentLineEdit;
    QLineEdit *inputMaskLineEdit;
    QLineEdit *accessLineEdit;
};

The slots are used to update the type of validator used for a given line edit when a new validator has been selected in the associated combobox. The line edits are stored in the window for use in these slots.

Window Class Implementation▲

The Window constructor is used to set up the line edits, validators, and comboboxes, connect signals from the comboboxes to slots in the Window class, and arrange the child widgets in layouts.

We begin by constructing a group box to hold a label, combobox, and line edit so that we can demonstrate the QLineEdit::echoMode property:

 
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Window::Window()
{
    QGroupBox *echoGroup = new QGroupBox(tr("Echo"));

    QLabel *echoLabel = new QLabel(tr("Mode:"));
    QComboBox *echoComboBox = new QComboBox;
    echoComboBox->addItem(tr("Normal"));
    echoComboBox->addItem(tr("Password"));
    echoComboBox->addItem(tr("PasswordEchoOnEdit"));
    echoComboBox->addItem(tr("No Echo"));

    echoLineEdit = new QLineEdit;
    echoLineEdit->setPlaceholderText("Placeholder Text");
    echoLineEdit->setFocus();

At this point, none of these widgets have been arranged in layouts. Eventually, the echoLabel, echoComboBox, and echoLineEdit will be placed in a vertical layout inside the echoGroup group box.

Similarly, we construct group boxes and collections of widgets to show the effects of QIntValidator and QDoubleValidator on a line edit's contents:

 
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    QGroupBox *validatorGroup = new QGroupBox(tr("Validator"));

    QLabel *validatorLabel = new QLabel(tr("Type:"));
    QComboBox *validatorComboBox = new QComboBox;
    validatorComboBox->addItem(tr("No validator"));
    validatorComboBox->addItem(tr("Integer validator"));
    validatorComboBox->addItem(tr("Double validator"));

    validatorLineEdit = new QLineEdit;
    validatorLineEdit->setPlaceholderText("Placeholder Text");

Text alignment is demonstrated by another group of widgets:

 
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    QGroupBox *alignmentGroup = new QGroupBox(tr("Alignment"));

    QLabel *alignmentLabel = new QLabel(tr("Type:"));
    QComboBox *alignmentComboBox = new QComboBox;
    alignmentComboBox->addItem(tr("Left"));
    alignmentComboBox->addItem(tr("Centered"));
    alignmentComboBox->addItem(tr("Right"));

    alignmentLineEdit = new QLineEdit;
    alignmentLineEdit->setPlaceholderText("Placeholder Text");

QLineEdit supports the use of input masks. These only allow the user to type characters into the line edit that follow a simple specification. We construct a group of widgets to demonstrate a selection of predefined masks:

 
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    QGroupBox *inputMaskGroup = new QGroupBox(tr("Input mask"));

    QLabel *inputMaskLabel = new QLabel(tr("Type:"));
    QComboBox *inputMaskComboBox = new QComboBox;
    inputMaskComboBox->addItem(tr("No mask"));
    inputMaskComboBox->addItem(tr("Phone number"));
    inputMaskComboBox->addItem(tr("ISO date"));
    inputMaskComboBox->addItem(tr("License key"));

    inputMaskLineEdit = new QLineEdit;
    inputMaskLineEdit->setPlaceholderText("Placeholder Text");

Another useful feature of QLineEdit is its ability to make its contents read-only. This property is used to control access to a line edit in the following group of widgets:

 
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    QGroupBox *accessGroup = new QGroupBox(tr("Access"));

    QLabel *accessLabel = new QLabel(tr("Read-only:"));
    QComboBox *accessComboBox = new QComboBox;
    accessComboBox->addItem(tr("False"));
    accessComboBox->addItem(tr("True"));

    accessLineEdit = new QLineEdit;
    accessLineEdit->setPlaceholderText("Placeholder Text");

Now that all the child widgets have been constructed, we connect signals from the comboboxes to slots in the Window object:

 
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    connect(echoComboBox, SIGNAL(activated(int)),
            this, SLOT(echoChanged(int)));
    connect(validatorComboBox, SIGNAL(activated(int)),
            this, SLOT(validatorChanged(int)));
    connect(alignmentComboBox, SIGNAL(activated(int)),
            this, SLOT(alignmentChanged(int)));
    connect(inputMaskComboBox, SIGNAL(activated(int)),
            this, SLOT(inputMaskChanged(int)));
    connect(accessComboBox, SIGNAL(activated(int)),
            this, SLOT(accessChanged(int)));

Each of these connections use the QComboBox::activated() signal that supplies an integer to the slot. This will be used to efficiently make changes to the appropriate line edit in each slot.

We place each combobox, line edit, and label in a layout for each group box, beginning with the layout for the echoGroup group box:

 
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    QGridLayout *echoLayout = new QGridLayout;
    echoLayout->addWidget(echoLabel, 0, 0);
    echoLayout->addWidget(echoComboBox, 0, 1);
    echoLayout->addWidget(echoLineEdit, 1, 0, 1, 2);
    echoGroup->setLayout(echoLayout);

The other layouts are constructed in the same way:

 
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    QGridLayout *validatorLayout = new QGridLayout;
    validatorLayout->addWidget(validatorLabel, 0, 0);
    validatorLayout->addWidget(validatorComboBox, 0, 1);
    validatorLayout->addWidget(validatorLineEdit, 1, 0, 1, 2);
    validatorGroup->setLayout(validatorLayout);

    QGridLayout *alignmentLayout = new QGridLayout;
    alignmentLayout->addWidget(alignmentLabel, 0, 0);
    alignmentLayout->addWidget(alignmentComboBox, 0, 1);
    alignmentLayout->addWidget(alignmentLineEdit, 1, 0, 1, 2);
    alignmentGroup-> setLayout(alignmentLayout);

    QGridLayout *inputMaskLayout = new QGridLayout;
    inputMaskLayout->addWidget(inputMaskLabel, 0, 0);
    inputMaskLayout->addWidget(inputMaskComboBox, 0, 1);
    inputMaskLayout->addWidget(inputMaskLineEdit, 1, 0, 1, 2);
    inputMaskGroup->setLayout(inputMaskLayout);

    QGridLayout *accessLayout = new QGridLayout;
    accessLayout->addWidget(accessLabel, 0, 0);
    accessLayout->addWidget(accessComboBox, 0, 1);
    accessLayout->addWidget(accessLineEdit, 1, 0, 1, 2);
    accessGroup->setLayout(accessLayout);

Finally, we place each group box in a grid layout for the Window object and set the window title:

 
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    QGridLayout *layout = new QGridLayout;
    layout->addWidget(echoGroup, 0, 0);
    layout->addWidget(validatorGroup, 1, 0);
    layout->addWidget(alignmentGroup, 2, 0);
    layout->addWidget(inputMaskGroup, 0, 1);
    layout->addWidget(accessGroup, 1, 1);
    setLayout(layout);

    setWindowTitle(tr("Line Edits"));
}

The slots respond to signals emitted when the comboboxes are changed by the user.

When the combobox for the Echo group box is changed, the echoChanged() slot is called:

 
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void Window::echoChanged(int index)
{
    switch (index) {
    case 0:
        echoLineEdit->setEchoMode(QLineEdit::Normal);
        break;
    case 1:
        echoLineEdit->setEchoMode(QLineEdit::Password);
        break;
    case 2:
        echoLineEdit->setEchoMode(QLineEdit::PasswordEchoOnEdit);
        break;
    case 3:
        echoLineEdit->setEchoMode(QLineEdit::NoEcho);
    }
}

The slot updates the line edit in the same group box to use an echo mode that corresponds to the entry described in the combobox.

When the combobox for the Validator group box is changed, the validatorChanged() slot is called:

 
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void Window::validatorChanged(int index)
{
    switch (index) {
    case 0:
        validatorLineEdit->setValidator(0);
        break;
    case 1:
        validatorLineEdit->setValidator(new QIntValidator(
            validatorLineEdit));
        break;
    case 2:
        validatorLineEdit->setValidator(new QDoubleValidator(-999.0,
            999.0