Press touch screen and hot plug the touch board, qt app(push button) cannot receive mousepress event, button click not work

Zonghua He

Before hot plug, the push button click can receive events:
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchBegin on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseMove on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseMove on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::HoverMove on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::MouseButtonPress on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::FocusAboutToChange on object: QRadioButton(0x55772319e0, name = "radioButton")
QEvent::FocusOut on object: QRadioButton(0x55772319e0, name = "radioButton")
QEvent::FocusOut on object: QWindowsStyle(0x557725dd80, name = "windows")
QEvent::FocusIn on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::FocusIn on object: QWindowsStyle(0x557725dd80, name = "windows")
QEvent::MouseButtonPress on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::UpdateRequest on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::Paint on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::Paint on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::Paint on object: QRadioButton(0x55772319e0, name = "radioButton")
QEvent::Paint on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::UpdateRequest on object: QLinuxFbScreen(0x55771da260)
QEvent::UpdateRequest on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchEnd on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseButtonRelease on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseButtonRelease on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::UpdateRequest on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::Paint on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::Paint on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::Paint on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::UpdateRequest on object: QLinuxFbScreen(0x55771da260)
QEvent::UpdateRequest on object: MainWindow(0x7fc53faeb0, name = "MainWindow")

But long press touch screen and hot plug touch board（at the same time），qt app print：
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchBegin on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseMove on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::Leave on object: QPushButton(0x557726fc50, name = "pushButton")
QEvent::MouseMove on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::HoverMove on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::MouseButtonPress on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseButtonPress on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::MouseButtonPress on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
Pressed position: x: 840 , y: 154
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchUpdate on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseMove on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseMove on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::MouseMove on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::HoverMove on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
[ 5184.073284] usb 3-1: USB disconnect, device number 4
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
qt.qpa.input: libinput: event3 - eGalax Inc. eGalaxTouch P80H46 2177 vT1_M00 k4.10.142: device removed
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchCancel on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::TouchCancel on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::MouseButtonRelease on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::MouseButtonRelease on object: QWidget(0x557725e400, name = "centralwidget")
QEvent::MouseButtonRelease on object: MainWindow(0x7fc53faeb0, name = "MainWindow")
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)

Systerm print after hot plug:
[ 5205.415988] usb 3-1: new full-speed USB device number 5 using ohci-platform
[ 5205.640536] usb 3-1: New USB device found, idVendor=0eef, idProduct=c002, bcdDevice=77.00
[ 5205.640614] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 5205.640649] usb 3-1: Product: eGalaxTouch P80H46 2177 vT1_M00 k4.10.142
[ 5205.640679] usb 3-1: Manufacturer: eGalax Inc.
[ 5205.656845] input: eGalax Inc. eGalaxTouch P80H46 2177 vT1_M00 k4.10.142 as /devices/platform/fd840000.usb/usb3/3-1/3-1:1.0/0003:0EEF:C002.0004/input/input13
[ 5205.713401] hid-multitouch 0003:0EEF:C002.0004: input,hiddev96,hidraw0: USB HID v1.11 Pointer [eGalax Inc. eGalaxTouch P80H46 2177 vT1_M00 k4.10.142] on usb-fd840000.usb-1/input0
QEvent:716455] panel-simple panel: Linked as a consumer to regulator.8
:SockA[ct on object: QSocketNotifier(0x5577206a00)
5205.716582] panel-simple panel: panel supply vsp not found, using dummy regulator
[ 5205.716696] panel-simple panel: panel supply vsn not found, using dummy regulator
[ 5205.717029] panel-simple panel: Dropping the link to regulator.8
[ 5205.718285] panel-simple rgb-panel: Linked as a consumer to regulator.8
[ 5205.718389] panel-simple rgb-panel: rgb-panel supply vsp not found, using dummy regulator
[ 5205.718492] panel-simple rgb-panel: rgb-panel supply vsn not found, using dummy regulator
[ 5205.718770] panel-simple rgb-panel: Dropping the link to regulator.8
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
qt.qpa.input: libinput: event3 - eGalax Inc. eGalaxTouch P80H46 2177 vT1_M00 k4.10.142: is tagged by udev as: Touchscreen
qt.qpa.input: libinput: event3 - eGalax Inc. eGalaxTouch P80H46 2177 vT1_M00 k4.10.142: device is a touch device
qt.qpa.input: libinput: registerDevice /dev/input/event3 - eGalax Inc. eGalaxTouch P80H46 2177 vT1_M00 k4.10.142

Click push button, can only receive:
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchBegin on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")
QEvent::SockAct on object: QSocketNotifier(0x5577206a00)
QEvent::TouchEnd on object: QWidgetWindow(0x5577289e50, name = "MainWindowWindow")

Qt app print code:
protected:
bool eventFilter(QObject *obj, QEvent *event) override
{
if (1) {
qDebug() << event->type() << " on object:" << obj;
}

    return QObject::eventFilter(obj, event); 
}

Linux aarch64, buildroot, kernal 4.19.206. QT version: 5.15.8.
Looking forward to your reply. Thanks for advance.

JoeCFD

Type the following into deepseek or grok, you may be able to find some clues.

Before hot plug, the push button click can receive events. But long press touch screen and hot plug touch board（at the same time. qt app(push button) cannot receive mousepress event, button click not work

Zonghua He

Hi JoeCFD, thanks for advice.

AI told me to reimplement event()：
//reimplement event()
bool MainWindow::event(QEvent *event)
{
QTouchEvent touchEvent = static_cast<QTouchEvent>(event);
qDebug() << "New event:" << touchEvent->type();

if (event->type() == QEvent::TouchBegin ||
    event->type() == QEvent::TouchUpdate ||
    event->type() == QEvent::TouchEnd) {

    QObject *target = childAt(touchEvent->touchPoints().first().pos().toPoint());
    qDebug() << "target: " << target;

    if (qobject_cast<QPushButton*>(target) ||
            qobject_cast<QRadioButton*>(target) ||
            qobject_cast<QComboBox*>(target) ||
            qobject_cast<QSlider*>(target) ||
            qobject_cast<QLineEdit*>(target) ||
            qobject_cast<QLabel*>(target) ||
            qobject_cast<QScrollBar*>(target)) {
        
        qDebug() << "++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Include.";
        return QWidget::event(event);
    }

    qDebug() << "++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Will return true.";

    return true;//if false,  event to QPushButton will not be deliver
}

qDebug() << "----------------------------------------------------------------- Will goto last return.";

return QMainWindow::event(event);

}

QPushButton，QRadioButton，QComboBox，QSlider，QLineEdit，QLabel，QScrollBar can work well.

But if the clicked object is QTableWidget, it will not work.

I have no idea how to fix it.

JoeCFD

@Zonghua-He Continue asking deepseek or grok.

JonB

@Zonghua-He said in Press touch screen and hot plug the touch board, qt app(push button) cannot receive mousepress event, button click not work:

QTouchEvent touchEvent = static_cast<QTouchEvent>(event);

One thing I don't get. How can you know that every MainWindow::event(QEvent *event) is going to be a QTouchEvent? Won't the static_cast barf if it is not?

JoeCFD

@JonB Good point!

JonB

@JoeCFD
Yes but I assumed (untested) that

QTouchEvent touchEvent = static_cast<QTouchEvent>(event);

would static-cast-except if it is not a QTouchEvent? Oh, I can't remember any more, doesn't static_cast throw ab exception where dynamic_cast would (for a pointer) return nullptr? Or is static_cast just the dangerous C cast, no exception? Yeah, I'm beginning to think it's that....

JoeCFD

@JonB
std::static_cast:
No runtime checks: If you downcast a pointer to a derived class incorrectly, it leads to undefined behavior.
Faster: No runtime overhead.

std::dynamic_cast:
Performs a runtime check to ensure the cast is valid.
For pointers: nullptr if the cast fails.
For references: Throws std::bad_cast if the cast fails.
Involves runtime type information (RTTI) overhead.

I think std::dynamic_cast is needed.

JonB

@JoeCFD
OK, I think I was confusing some "static cast" in C# which did "assert" if incorrect. Got it.

I don't think you can use dyanmic_cast here because event is not a pointer here? dynamic_cast<QTouchEvent>(event) would not be able to return its usual nullptr if wrong type, so I don't see how you can here?

JoeCFD

@JonB bool MainWindow::event(QEvent *event)

JonB

@JoeCFD
Here is is copied verbatim from what OP posted in https://forum.qt.io/post/823816 above:

bool MainWindow::event(QEvent *event)
{
QTouchEvent touchEvent = static_cast<QTouchEvent>(event);

That is static_cast<QTouchEvent>, not static_cast<QTouchEvent *>. I think I get it. OP did not use ``` :( So the * asterisk for pointer did italic instead of visible. That's the problem with no Code tags :( I get it now, misunderstanding.

Zonghua He

@JonB Hi，thanks for your idea.

My code is not safe. Should be:
bool MainWindow::event(QEvent *event)
{
if (event->type() == QEvent::TouchBegin ||
event->type() == QEvent::TouchUpdate ||
event->type() == QEvent::TouchEnd) {
QTouchEvent touchEvent = static_cast<QTouchEvent>(event);
qDebug() << "New event:" << touchEvent->type();

    QObject *target = childAt(touchEvent->touchPoints().first().pos().toPoint());
    qDebug() << "target: " << target;

    if (qobject_cast<QPushButton*>(target) ||
            qobject_cast<QRadioButton*>(target) ||
            qobject_cast<QComboBox*>(target) ||
            qobject_cast<QSlider*>(target) ||
            qobject_cast<QLineEdit*>(target) ||
            qobject_cast<QLabel*>(target) ||
            qobject_cast<QScrollBar*>(target)) {
        qDebug() << "++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Include.";
        return QMainWindow::event(event);
    }

    qDebug() << "++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Will return true.";

    return true;//if false, QPushButton will not be deliver
}

qDebug() << "----------------------------------------------------------------- Will goto last return.";

return QMainWindow::event(event);

}

Do you have any idea about my problem? After hot plug touch board usb cable(finger is touching on screen at the same time), all the pushbuttons, sliders and so on, can not response. But if i hot plug the touch board usb cable without touching the touch screen, all is well. This problem always occurs on widget app. The QML app works well.

Kevin Hoang

Based on the log you provided, the system correctly recognizes your touchscreen after reconnecting. However, Qt has detected the device as a touchscreen through libinput (event3). This means that Qt is handling touch events instead of mouse events.

You might want to try adding QCoreApplication::setAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents); in your main application to see if that resolves the issue.

Zonghua He

@Kevin-Hoang said in Press touch screen and hot plug the touch board, qt app(push button) cannot receive mousepress event, button click not work:

orUnhandled

Hi Kevin Hoang, I did what you told me. But also not work.
My project is : https://github.com/hezonghua/linux_QT_touch_screen_widget_app

I will appreciate if you can have a look at my project. Thanks for advance.

JonB

@Zonghua-He
Please use the forum posts' Code tags (the </> button, or a line of ``` above and below) when posting blocks of code if you wish to avoid the incorrect code you show and my misunderstanding about what you actually have.

I am sorry but I do not know about your problem.

Zonghua He

@JonB Thanks for your advice.

Kevin Hoang

I really don’t have time to help you, but I noticed that when you unplug the screen, the TouchCancel event is triggered (TouchCancel also causes MouseButtonRelease to be sent to all widgets for processing). I suspect that during the TouchCancel process, something gets stuck, preventing proper event handling when you plug the screen back in.

Since the Qt version you’re using is quite old, I’m not sure if there’s any existing bug related to this.

You might try calling QApplication::processEvents() in the screenAdd event and see if that helps.

Also, before unplugging the screen (when everything is working fine), check whether the Input DeviceType is TouchScreen and compare if there are any differences between the initial state of the application and the state after hot-plugging.