Need support for model interface to set on views about qml

[niemeyer]

For the record, working with model views is already possible and convenient today via the indexed mechanism.

Here is a good example:

• http://github.com/niemeyer/qml/blob/master/examples/modelview/delegate

Let's keep this bug open, though, as there might be advantages in supporting an implementation of QAbstractItemModel.

[michael-k]

Regarding TableViews, I had the problem, that role did not work. (At least I could not find out how to get it to work. So I use this workaround:

TableView {
    model: contactList.len

    TableViewColumn {
        title: qsTr("Name")
        delegate: Item {
            Text {
                anchors.verticalCenter: parent.verticalCenter
                color: styleData.textColor
                elide: styleData.elideMode
                text: contactList.name(styleData.row)
            }
        }
    }
}

[quarnster]

Is there an efficient way to remove/add a single item out of 1000 with the index model?

Just setting model = array.length will re-create all 999/1001 elements rather than just tweak the single one that was changed.

[quarnster]

To answer myself; yes there is. For example:

    ListModel {
        id: myModel
    }
...
    myModel.append({"itemId":rs.item(i).id});

itemId will then exist as a variable in the delagate component that is created as a result. myModel can be located from go so that its functions can be called from there if one wants to.

[NSkelsey]

@quarnster I am trying to figure out what you did here. Is there any chance you could elaborate?

[quarnster]

Sure, here's a quick freestanding example:

package main

import (
    "gopkg.in/qml.v1"
    "log"
)

var qmlFile = `
import QtQuick 2.3
import QtQuick.Controls 1.2
import QtQuick.Layouts 1.0

ApplicationWindow {
    id: main
    width: 800
    height: 600

    function validate() {
        for (var i = 0; i < gomodel.len(); i++) {
            var godata = gomodel.get(i);
            var qmldata = lmodel.get(i).goitem;
            // Note that "godata" and "qmldata" are not
            // pointing to the same address though...
            if (godata.text != qmldata.text) {
                console.log(godata.text, qmldata.text);
            }
        }
    }
    function insert(i, data) {
        lmodel.insert(i, {"goitem": data});
        validate();
    }
    function removed(i) {
        lmodel.remove(i);
        validate();
    }
    ListModel {
        id: lmodel
    }
    ColumnLayout {
        Button {
            text: "add"
            onClicked: {
                console.log("adding!!");
                gomodel.add("Item " + Math.floor(Math.random()*1024));
            }
        }
        Button {
            text: "remove"
            onClicked: {
                console.log("removing!!");
                gomodel.remove(lv.currentIndex);
            }
        }

        ScrollView {
            Layout.fillHeight: true
            ListView {
                id: lv
                model: lmodel
                height: contentHeight
                delegate: Rectangle {
                    id: item
                    color: lv.currentIndex == index ? Qt.rgba(0.9,0.9,0.9,1.0) : "white"
                    width: Math.max(t.width, parent.width)
                    height: t.height
                    clip: true
                    Text {
                        id: t
                        text: goitem.text
                    }
                    MouseArea {
                        anchors.fill: parent
                        onClicked: lv.currentIndex = index
                    }
                }
            }
        }
    }
}
`

var window *qml.Window

type (
    Item struct {
        Text string
    }
    Model struct {
        items []*Item
    }
)

func (m *Model) Add(text string) {
    i := len(m.items)
    m.items = append(m.items, &Item{text})
    window.Call("insert", i, m.items[i])
}

func (m *Model) Remove(i int) {
    copy(m.items[i:], m.items[i+1:])
    m.items = m.items[:len(m.items)-1]
    window.Call("removed", i)
}

func (m *Model) Len() int {
    return len(m.items)
}

func (m *Model) Get(i int) *Item {
    return m.items[i]
}

func main() {
    model := &Model{}
    log.Println(qml.Run(func() error {
        engine := qml.NewEngine()
        defer engine.Destroy()
        engine.Context().SetVar("gomodel", model)
        component, err := engine.LoadString("main.qml", qmlFile)
        if err != nil {
            return err
        }
        window = component.CreateWindow(nil)
        window.Show()
        window.Wait()
        return nil
    }))
}

[NSkelsey]

@quarnster Thanks for the response. That window.Call in Add is very clever! I would not have thought of that.

This should be added to the delegate dir of the examples.

[pjoe]

Though putting things through a QML ListModel is workable, in my experience that won't perform anything near the QAbstractItemModel, that can efficiently signal changes in the model directly to the QML ListView, see e.g. beginInsertRows/endInsertRows. This is especially true if you are doing insertion/removal of mutliple items at once. So having a way to implement this QAbstractItemlModel interface in go would be really cool :D

[pjoe]

Ohh I just saw that there is already a list-model branch with some work in progress for this, anything we can do to help?

[niemeyer]

I'm not sure. The main blocker is researching in depth how to implement these interfaces in a sane way, and the reason it's taking so long is because the interface seems extensive and non-trivial on the C++ side. Whatever we do needs to be straightforward and sensible, and I haven't managed to work on it enough to get to that point.

[filcuc]

Niemeyer we should get in contact. I'm the author of the DOtherSide project that bring Qml bindings for Nim and D. I worked on this topic maybe i can share my implementation and see if it works for you too.

[pjoe]

Also lemme know if there is anything i can do to help. I have been using QAbstractItemList for interfacing C++ and QML for several years by now (since sometime from Qt 4.7beta). I'm on IRC freenode (as pjoe or pjoe_dj) during daytime CET