ListView: Long press and release to initiate a grab, move mouse to scroll, then click to release

mbarclaygmail.com

Hello,

I am trying to figure out how to change the way ListView responds to mouse events. I have a large, scrollable list, and I want to "long press" on the ListView widget to initiate scrolling. After the long press (and release), the list is "grabbed" and any movement of the mouse along the y-axis should result in scrolling of the List. A single click should release grabbed list.

Is this possible?

Thanks,
Matt

DenisKormalev

I think that it is possible only by custom plugin with class inherited from listview (or maybe from flickable). Not sure, but I'll be at your place I will start from this point while solving this issue.

2beers

I think you should look at the Flickable scrollbar example( I can't find the link now but is somewhere in docs) . after the long press action you scroll your flickable element(I think it will work for listview) on y-axis based on your mouse position.

DenisKormalev

2beers, hm, can't find how to track mouse without buttons pressed

mbarclaygmail.com

Hmm, I thought I was being clever, but this doesn't work. When I try to set grabMouse() on the ListView, the program crashes. On the MouseArea, QGraphics complains there is no scene.

@class MySystem : public QObject
{
Q_OBJECT
Q_INVOKABLE void grabMouse(QDeclarativeItem *item) { if(item) item->grabMouse(); }
};

int main(void)
{
...
...
view.rootContext()->setContextProperty("mysys", new MySystem());
}

QML

Item {
ListModel { id: myModel; ListElement { type: "Dog"; age: 8 } ListElement { type: "Dog"; age: 8 } }
Component { id: myDelegate; Text { text: type + ", " + age } }
ListView {
id: myList
model: myModel
delegate: myDelegate
MouseArea {
id: mymouse
anchors.fill: parent
onPressAndHold: {
// This crashes:
mysys.grabMouse(myList);

            // This complains:  QGraphicsItem::grabMouse: cannot grab mouse without scene
            // mysys.grabMouse(mymouse);
   
            // This complains: QGraphicsItem::grabMouse: cannot grab mouse while invisible
            // mysys.grabMouse(listItem)
     }
  }

}
}
@

mbarclaygmail.com

Thinking out loud here, I could create a MouseGrabArea class similar to MouseArea...

No idea if something like this would work, but will try tomorrow:

@ListView {
id: mylist

MouseGrabArea { height: parent.height; width: parent.width; }
...
...
}

// Psuedo code...
class MouseGrabArea : public QDeclarativeItem
{
public slot:
void onMousePress() { m_press_time = gettime(); } // Time in milliseconds
void onMouseRelease() { if(gettime() - m_press_time > 800) { this.grabMouse(); } else { this.releaseMouse(); } }
};
@

mbrasser

Hi,

Are you looking for standard "flicking" behavior after the long press, or just panning? If the latter, putting a MouseArea over the ListView, and using it to manually manipulate the ListView's position (using e.g. positionViewAtIndex, or contextX/Y) might work.

Regards,
Michael

mbarclaygmail.com

I solved this with a little help from C++. Using rootContext->setContextProperty(), I created a C++ class with Q_INVOKABLE methods that:

@setGrabCursor(bool doit) const
{
if(doit)
QApplication::setOverrideCursor(QCursor(Qt::ClosedHandCursor));
else
QApplication::restoreOverrideCursor();
}@

From my app, when I detect a long press on my ListView delegate, I call setGrabCursor(true) and make a full screen mousearea active that marks mouse events as accepted. I tie the mouse y coordinate to the listview contentY inside of a onPositionChanged() handler. On single click of the mousearea, I call setGrabCursor(false).