[Qt-qml] Forwarding mouse events to MouseArea underneath

[Gregory Schlomoff]

Thanks Alan,

Added a commentwith our use-case and workaround on this bug.

http://bugreports.qt.nokia.com/browse/QTBUG-13007?focusedCommentId=137123#comment-137123

On Mon, Jan 10, 2011 at 9:11 AM, Alan Alpert <alan.alpert at nokia.com> wrote:
> On Friday, January 07, 2011 08:54:33 pm ext Gregory Schlomoff wrote:
>> > http://doc.qt.nokia.com/4.7-snapshot/qml-mouseevent.html#accepted-prop ?
>>
>> Yeah, you'd think that's what this property was made for. And you'd be
>> wrong :)
>>
>> MouseEvent.accepted seems perfectly useless, but in very specific
>> cases, like in onDoubleClicked.
>>
>> http://doc.qt.nokia.com/main-snapshot/qml-mousearea.html#onClicked-signal
>> --> "The accepted property of the MouseEvent parameter is ignored in
>> this handler."
>>
>> On Fri, Jan 7, 2011 at 5:50 PM, Juha Turunen <turunen at iki.fi> wrote:
>> > http://doc.qt.nokia.com/4.7-snapshot/qml-mouseevent.html#accepted-prop ?
>> >
>> > On Fri, Jan 7, 2011 at 11:51 AM, Gregory Schlomoff
>> >
>> > <gregory.schlomoff at gmail.com> wrote:
>> >> Hello,
>> >>
>> >> We are in a situation where we have one big MouseArea on top handling
>> >> click events and several smaller MouseAreas below handling
>> >> double-click events.
>> >>
>> >> Unfortunately, there is currently no way in QML to say that an event
>> >> should "bubble" up or down to the next receiver. The top MouseArea
>> >> will always catch all events, and the MouseAreas below will get
>> >> nothing.
>> >>
>> >> There is a very specific solution when the event you want to handle in
>> >> the topmost MouseArea is onDrag. In this case, you can use
>> >> drag.filterChildren: true to let the topmost MouseArea catch only drag
>> >> event and pass other events to MouseAreas beneath. But it won't work
>> >> for other events.
>> >>
>> >> We devised a ugly hack to work around this, that basically involves
>> >> catching the event in the topmost MouseArea and manually calling the
>> >> event handler on any MouseArea underneath:
>> >>
>> >> ===============
>> >> import QtQuick 1.0
>> >>
>> >> Rectangle {
>> >>        width: 360
>> >>        height: 360
>> >>
>> >>        MouseArea {
>> >>                anchors {fill: parent; margins: 40}
>> >>                onClicked: console.log("hello from below");
>> >>        }
>> >>
>> >>        MouseArea {
>> >>                id: mouseArea
>> >>                anchors.fill: parent
>> >>
>> >>                onClicked: {
>> >>                        console.log("hello from top")
>> >>                        forwardEvent(mouse, "clicked");
>> >>                }
>> >>
>> >>                function forwardEvent(event, eventType) {
>> >>                        mouseArea.visible = false
>> >>                        var item = parent.childAt(event.x, event.y)
>> >>                        mouseArea.visible = true
>> >>                        if (item && item != mouseArea &&
>> >> typeof(item[eventType]) == "function") { item[eventType](event);
>> >>                        }
>> >>                }
>> >>        }
>> >> }
>> >> ===============
>> >>
>> >> What do you think? Are there any better solutions? Should this be a
>> >> built-in functionnality in QML so that we can avoid this hack,
>> >> especially the fact that we have to hide / show the element to get
>> >> elements below. Any feedback is appreciated.
>> >>
>> >> Thanks,
>> >>
>> >> Greg
>
> Sounds like you want http://bugreports.qt.nokia.com/browse/QTBUG-13007 .
> Currently scheduled for 4.8; you might want to watch or vote for that task,
> and adding a comment with a concrete usecase is always helpful.
>
> --
> Alan Alpert
> Software Engineer
> Nokia, Qt Development Frameworks
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