How to connect LineEdit and PushButton in Qt?

Question

I created a .ui file using Qt Designer and in the file I created a PushButton which is disabled initially, I also have a LineEdit. I want to connect LineEdit and PushBotton so that when text changed in LineEdit , the PushButton will be enabled, But I don't find any such option in Signals and slots. Can anyone help?

connect `textChanged(const QString & text)` with a custom slot that calls `pushButton->setEnabled(true)`. I think you may want also to check `text.isEmpty()` into that slot — Miki, Jul 04 '15 at 17:52
@Miki I am using Qt 4.8 Designer , I am creating ui files not coding. — Madhu Kumar Dadi, Jul 04 '15 at 17:55
I'm pretty sure you can / have to write your custom slots... http://stackoverflow.com/questions/7964869/qt-designer-how-to-add-custom-slot-and-code-to-a-button — Miki, Jul 04 '15 at 17:56
I'm saying that I don't think that you have a _standard_ slot that fits your needs, so write your own. You should still be able to connect to that slot in the Designer. — Miki, Jul 04 '15 at 18:02
Can we add slots to designer? I mean can I create a slot to the Designer? — Madhu Kumar Dadi, Jul 04 '15 at 18:03
We can create custom slots to the Designer. Check here http://stackoverflow.com/questions/165637/how-do-i-create-a-custom-slot-in-qt4-designer — Madhu Kumar Dadi, Jul 04 '15 at 18:18

kefir500 · Accepted Answer · 2015-07-04T18:20:56.550

4

You have to write a custom slot (which is pretty easy).

Add this to your MainWindow declaration (.h file):

private slots:
    void checkInput(const QString &text);

Your .cpp file:

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->lineEdit, SIGNAL(textChanged(QString)), this, SLOT(checkInput(QString)));
}

void MainWindow::checkInput(const QString &text)
{
    ui->pushButton->setEnabled(!text.isEmpty());
}

To add this slot to Qt Designer, do the following:

Right click on your MainWindow, "Change signals/slots";
Add your custom slot ("Plus" button) by entering checkInput();
After this you will be able to connect your custom slot via Qt Designer.

edited Jul 04 '15 at 18:20

answered Jul 04 '15 at 18:06

kefir500

4,184
6
42
48

How can I add this to Designer?? – Madhu Kumar Dadi Jul 04 '15 at 18:08
When I right click on the Form I am not getting any option to change signals/slots. – Madhu Kumar Dadi Jul 05 '15 at 15:12
You can also get this dialog by pressing "Edit..." button in the "Configure Connection" window when connecting signals/slots (F4). – kefir500 Jul 06 '15 at 12:26
1

This slot is a MainWindow member, that is why it works for MainWindow. For this particular case you'll need to connect LineEdit and MainWindow (not your button) signal and slot. – kefir500 Jul 06 '15 at 12:52
And how can I define the slot() when I create one for MainWindow. – Madhu Kumar Dadi Jul 06 '15 at 13:43
What do you me by "define the slot()"? When connecting `LineEdit` to `MainWindow` via Qt Designer, the `Edit...` button should be enabled. – kefir500 Jul 06 '15 at 15:31
Yes, there I am adding slots but how to define those slots. – Madhu Kumar Dadi Jul 07 '15 at 02:35
Slot definition is already in the answer. The slot is declared in the header file and defined as a usual member function in the cpp. What exactly is the problem? – kefir500 Jul 07 '15 at 06:48

Kuba hasn't forgotten Monica · Answer 2 · 2016-06-23T17:16:43.827

1

In Qt 5, you generally don't need trivial private slots and should use lambdas instead:

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->lineEdit, &QLineEdit::textChanged, [this](const QString & text) {
      ui->pushButton->setEnabled(!text.isEmpty());
    });
    ...
}

edited Jun 23 '16 at 17:16

answered Jul 06 '15 at 12:50

Kuba hasn't forgotten Monica

95,931
16
151
313

How to connect LineEdit and PushButton in Qt?

2 Answers2