ListView - Why Space key is never received in Keys.onPressed() signal?

[jeanmilost]

In a ListView I'm creating, I need to intercept the Space key, to allow to perform a special action onto the focused item instead of the default view behavior. For that reason I tried to listen the Keys.onPressed signal from inside my ListView component, and to intercept the Space key. However I noticed that this key is never sent to the Keys.onPressed signal, although the other keys are working as expected.

I also tried the Keys.onSpacePressed signal, but it's the same issue: the signal is just never called.

Why this happens, and how can I intercept the Space key in a ListView component?

[ODБOï]

@jeanmilost hi
Make sure focus property is set to true on the ListView
and there is nothing that takes the focus in your listview delegate

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    ListView{
        id: view
        anchors.fill: parent
        model :  ListModel{
            ListElement{
                name :  "el1"
            }
            ListElement{
                name :  "el2"
            }
            ListElement{
                name :  "el3"
            }
        }
        spacing: 2
        focus: true
        delegate: Button{
            focus: false
            focusPolicy: Qt.NoFocus
            onFocusChanged: if(focus)focus=false
            width: parent.width
            height: 50

            text : index === view.currentIndex ? "currentIndex" :  modelData

            onClicked: {
                view.currentIndex = index
            }
        }

        Keys.onPressed: {
              if (event.key === Qt.Key_Space) {
                  console.log("space clicked");                
                  console.log(view.model.get(view.currentIndex).name) // view.model.get(ind).name = "new value"
                  event.accepted = true;
              }
          }
    }
}

[jeanmilost]

@LeLev Thank you very much for your answer. It helped me to understand my issue a little more. So I tried your code, and it works, meaning that the ListView isn't eating the Space key.

However my interface is a little more complex than this one, it contains other objects like SwipeView, and yes, my items contain components like buttons which may take the focus. However I already tried to deactivate them and even thus the issue remained.

I played a while around the code you posted. I noticed that the following code no longer receives any key:

Rectangle
{
    anchors.fill: parent
    color: "transparent"
    visible: true

    SwipeView
    {
        anchors.fill: parent
        activeFocusOnTab: false

        Page
        {
            background: null

            ListView
            {
                id: view
                anchors.fill: parent
                spacing: 2
                focus: true

                model: ListModel
                {
                    ListElement
                    {
                        name:  "el1"
                    }

                    ListElement
                    {
                        name:  "el2"
                    }

                    ListElement
                    {
                        name:  "el3"
                    }
                }

                delegate: Button
                {
                    focus: false
                    focusPolicy: Qt.NoFocus
                    onFocusChanged: {if (focus) focus = false;}
                    width: parent.width
                    height: 50

                    text: index === view.currentIndex ? "currentIndex" :  modelData

                    onClicked:
                    {
                        view.currentIndex = index
                    }
                }

                Keys.onPressed:
                {
                    console.warn("key clicked");

                    if (event.key === Qt.Key_Space)
                    {
                        console.log("space clicked");
                        console.log(view.model.get(view.currentIndex).name); // view.model.get(ind).name = "new value"
                        event.accepted = true;
                    }
                }
            }
        }
    }
}

So I assume that some components operate like filters and may stop internally the keyboard signals, or at least a part of them, without let the choice to the developer to bypass this behavior (or at least I don't know how to do). To be honest I'm a little puzzled, because I worked for15 years with the Windows API before changing for Qt, and receiving a keyboard notification was never an issue, even when the parent component already received it before (in fact it was the contrary: the message could be blocked in the parent, but by default it was passing).

So now the question is: in the above code, how can I receive the keyboard signals, and in particular the Space key, in my ListView despite of the parent SwipeView? Or which solution is normally used in a such situation, e.g is there a way to globally listen the keyboard and intercept keys in the Windows level, BEFORE any component receives them?