How to emit a signal if double clicking on slider handle

Question

We are using Qt 5.10/C++ and I'm asked to implement a feature using the QSlider class.

My colleague wants me to emit a signal, whenever the user performs a double mouse click on the slider handle.

How can this be achieved. Maybe I have to reimplement

bool event(QEvent *e)

, but I don't know how to start.

There is a [`QWidget::mouseDoubleClickEvent()`](http://doc.qt.io/qt-5/qwidget.html#mouseDoubleClickEvent). According to doc., it doesn't seem to be overloaded in [`QSlider`](http://doc.qt.io/qt-5/qslider.html). If deriving from `QSlider` is an option, you may overload it in a derived class. (Otherwise, you may look for [event filters](http://doc.qt.io/qt-5/eventsandfilters.html#event-filters).) — Scheff's Cat, Sep 28 '18 at 07:48
@Scheff: Thanks for the hint. I'll give it a try. Deriving from QSlider is an option for me. — Aleph0, Sep 28 '18 at 07:50
You're welcome. If you manage to make a working minimal example, don't hesitate to write a self-answer. ;-) — Scheff's Cat, Sep 28 '18 at 07:52
As an alternative to overriding `QWidget::mouseDoubleClickEvent` you could [install an event filter](http://doc.qt.io/qt-5/qobject.html#eventFilter) on the `QSlider`. — G.M., Sep 28 '18 at 08:06
@Scheff: I tried using `QWidget::mouseDoubleClickEvent()` and there is an reaction to a mouse double click. Unfortunately, there is also an reaction to the double click, in case I'm not clicking on the slider handle. How can I separate the double click on the slider handle from other double clicks? — Aleph0, Sep 28 '18 at 08:08
In such cases, I have a look into `QStyle`: [Styles and Style Aware Widgets](http://doc.qt.io/qt-5/style-reference.html). There are many methods to draw controls but you will find also methods to retrieve rectangles of sub-controls. (Sorry for being not more specific - I'm a bit in hurry.) — Scheff's Cat, Sep 28 '18 at 08:13
@Scheff: No problem. You already helped a a lot. I just needed a starting point. — Aleph0, Sep 28 '18 at 08:14
Please, don't edit the answer into the question. Write it as (self) answer (and roll back your question to previous version). ([This is the recommended way](https://stackoverflow.com/help/self-answer).) After 48 hours you may accept it as _the_ answer. Btw. it could be worth for additional rep. points if other stumble into it and find it valuable. — Scheff's Cat, Sep 29 '18 at 06:45
@Scheff: Many thanks for the hint. I just answered my own question. — Aleph0, Oct 01 '18 at 05:44

score 3 · Accepted Answer · answered Oct 01 '18 at 05:43

Working solution

With the help of the comments I derived a working solution:

#pragma once

#include <QSlider>
#include <QMouseEvent>
#include <QStyleOption>
#include <QDebug>

class DoubleClickSlider : public QSlider {
    Q_OBJECT
public:
    DoubleClickSlider(QWidget* parent = nullptr) : QSlider(parent) { };

signals:
    void sliderHandleDoubleClicked();

protected:
    void mouseDoubleClickEvent(QMouseEvent *event) override {
        QStyleOptionSlider opt;
        this->initStyleOption(&opt);
        QRect sr = this->style()->subControlRect(QStyle::CC_Slider, &opt, QStyle::SC_SliderHandle, this);

        if (sr.contains(event->pos())) {
            qDebug() << "Double clicked handle";
            emit sliderHandleDoubleClicked();
        }
        QSlider::mouseDoubleClickEvent(event);

    }
};

How to emit a signal if double clicking on slider handle

1 Answers1