MouseArea works incorrectly inside TableView's delegate

[jeremy_k]

I have an idea of what's happening, although some of the details are still fuzzy.
Sorry about the large example. Move the cursor to the box in the left side displaying "0->1". This middle row should turn yellow. Click and it should change to "1->2". Click again and it goes back to 0->1. The pseudo-highlight does some interesting things.

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 640
    height: 480
    visible: true

    ListModel {
        id: lm
        ListElement { data: 0 }
        ListElement { data: 1 }
        ListElement { data: 2 }
    }

    ListView {
        anchors.fill: parent
        model: lm
        delegate: Rectangle {
            width: ListView.view.width
            height: 30
            color: ma.containsMouse ? "yellow" : "white"
            MouseArea {
                id: ma
                anchors.fill: parent
                hoverEnabled: true
                onContainsMouseChanged: print("containsMouse", containsMouse, model.data)
            }
            Text {
                anchors.centerIn: parent
                text: model.data
            }
        }
    }

    Rectangle {
        id: button
        width: 100
        height: 30
        y: 30
        border.width: 1
        border.color: "black"
        property int moveStart
        Text {
            anchors.centerIn: parent
            text: button.moveStart + "->" + (button.moveStart + 1)
        }
        MouseArea {
            anchors.fill: parent
            onClicked: button.moveStart == 0 ? button.moveStart = 1 : button.moveStart = 0
        }
    }

    Timer {
        interval: 1000
        onTriggered: lm.move(button.moveStart, button.moveStart + 1, 1)
        running: true
        repeat: true
    }
}

Under some circumstances, the model and view being reordered doesn't cause the the MouseArea to detect that it no longer contains the cursor, which results in the pseudo-highlight remaining with the item as it moves around the view. In other circumstances, the MouseArea does detect, which results in the flicker of the highlight from the old item to the new. One of these two is likely a Qt bug. I'm not sure which.

Ignoring the potential framework defect:

• How does the user reliably select an item if it frequently changes position?
• If the user does successfully select, is the highlight supposed to stay with the item when it moves, or jump to the new item under the cursor?

Making the selection click-based rather than hover-based solves the second problem. The first problem remains, unless the interface is intentionally a game of chance.

[Dmitriano]

@fcarney To test my model with QAbstractItemModelTester I added the following code to my function getAllMarkets() that created the model:

QObject * ExchangeListModel::getAllMarkets()
{
    //Creating the model p_table...

    new QAbstractItemModelTester(p_table);

    return p_table;
}

but I did not notice some messages in the application output.

[Dmitriano]

@jeremy_k Basically your example with ListView works, see the video: https://youtu.be/NZW5jHFpAlU (but the star periodically jumps away
from the cursor a bit).

Item {
    id: root
    property alias model: list.model

    ListView {
        id: list
        anchors.fill: parent

        delegate: Text {
            text: item.base + (ma.containsMouse ? " *" : "")
            MouseArea {
                id: ma
                anchors.fill: parent
                hoverEnabled: true
            }
        }
    }
}

note that I use not model.item.base but item.base.

But when I use the same delegate with my TableView the star jumps randomly between the cells, see https://youtu.be/3Br8jsX7f-E

Item {
    id: root
    property alias model: table.model

    TableView {
        id: table
        anchors.fill: parent
        columnSpacing: 1
        rowSpacing: 3
        clip: true

        property var columnWidths: [100, 90, 90, 60, 60];
        columnWidthProvider: function (column) { return columnWidths[column] }

        delegate: Text {
            text: model.item.base + (ma.containsMouse ? " *" : "")
            MouseArea {
                id: ma
                anchors.fill: parent
                hoverEnabled: true
            }
        }
    }
}

[Dmitriano]

@jeremy_k As I mentioned in my first post, the clicks are also handled incorrectly. (A wrong url is opened in the browser.)

[Dmitriano]

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

How does the user reliably select an item if it frequently changes position?
If the user does successfully select, is the highlight supposed to stay with the item when it moves, or jump to the new item under the cursor?

1. The user attempts to select the item he sees at he moment and if an attempt was unsuccessful, he retries. Or the user presses 'Freeze' button that stops sorting and selects an item from the static list. Or, theoretically, the update frequency can be configured somehow.

2. If the user does successfully select the item some page are added to a StackView above the TableView (and TableView becomes invisible), so the highlight disappares.

And I mentioned in my first post, the clicks are also handled incorrectly. (A wrong url is opened in the browser.)

So is this a TableView's bug? Should it be reported?

[jeremy_k]

@Dmitriano said in MouseArea works incorrectly inside TableView's delegate:

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

How does the user reliably select an item if it frequently changes position?
If the user does successfully select, is the highlight supposed to stay with the item when it moves, or jump to the new item under the cursor?

1. The user attempts to select the item he sees at he moment and if an attempt was unsuccessful, he retries. Or the user presses 'Freeze' button that stops sorting and selects an item from the static list. Or, theoretically, the update frequency can be configured somehow.

For some reason this reminds me of a claw crane.

2. If the user does successfully select the item some page are added to a StackView above the TableView (and TableView becomes invisible), so the highlight disappares.

And I mentioned in my first post, the clicks are also handled incorrectly. (A wrong url is opened in the browser.)

The MouseArea might be grabbing the mouse, in which case it will also receive the press and release events.

So is this a TableView's bug? Should it be reported?

I'm leaning toward the MouseArea being responsible, whether a bug or misuse. You didn't mention which TableView this is using. The Qt Quick Controls 1 version has a few signals for handling user selection. The TableView in QtQuick starting from 5.12 doesn't seem to have as rich of an API, but perhaps the UI can be implemented with a single stationary MouseArea that covers the entire view and finds the correct delegate with Item.childAt(), and the Flickable.contentItem.

[Dmitriano]

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

For some reason this reminds me of a claw crane.

Yes, it can be strange for some users, so theoretically, such kind of the uses will temporarily disable the sorting and then click on a row.

You didn't mention which TableView this is using.

I am using TableView 2.0

but perhaps the UI can be implemented with a single stationary MouseArea that covers the entire view and finds the correct delegate with Item.childAt(), and the Flickable.contentItem.

What Item.childAt() is? How to use it? Currently I use MouseArea in a similar way, see the code:

    TableView {
        id: table

        property var columnWidths: [100, 80, 80, 120];
        columnWidthProvider: function (column) { return columnWidths[column]; }

        property var rowHeight: 40
        rowHeightProvider: function (column) { return rowHeight; }

        MouseArea
        {
            id: ma
            anchors.fill: parent
            hoverEnabled: true
            onClicked: {
                var index = Math.floor(mouse.y / (table.rowHeight + table.rowSpacing));
                console.log(index, " ", mouse.x, " ", mouse.y, " ", table.contentX, " ", table.contentY)
                var item = table.model.rowKey(index)
                window.openMarket(item)
            }
        }

        delegate: DelegateChooser {
            role: "type"
            DelegateChoice {
                roleValue: "symbol"
                delegate: SymbolCell { item: model.item }
            }
        }
        ...
    }

it works with a fixed row height that I define with rowHeight property.

[fcarney]

@Dmitriano said in MouseArea works incorrectly inside TableView's delegate:

To test my model with QAbstractItemModelTester I added the following code to my function getAllMarkets() that created the model:

Put it in the constructor. Set it to warn so it doesn't kill the app on you.

[jeremy_k]

@Dmitriano said in MouseArea works incorrectly inside TableView's delegate:

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

but perhaps the UI can be implemented with a single stationary MouseArea that covers the entire view and finds the correct delegate with Item.childAt(), and the Flickable.contentItem.

What Item.childAt() is? How to use it? Currently I use MouseArea in a similar way, see the code:

https://doc.qt.io/qt-5/qml-qtquick-item.html#childAt-method

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 100
    height: 100
    visible: true

    Flickable {
        id: flickable
        anchors.fill: parent
        Repeater {
            id: repeater
            model: 10
            delegate: Rectangle {
                border.color: "black"
                border.width: 1
                width: 20
                height: 20
                x: index * 40
                y: x
            }
        }
    }

    Timer {
        interval: 1000
        running: true
        repeat: true
        onTriggered: {
            for (var index in flickable.contentItem.children) {
                var item = flickable.contentItem.children[index]
                item.x = Math.floor(Math.random() * flickable.contentItem.width);
                item.y = Math.floor(Math.random() * flickable.contentItem.height);
            }
            mouseArea.updateHighlight();
        }
    }

    MouseArea {
        id: mouseArea
        anchors.fill: flickable
        hoverEnabled: true
        property Item lastItem: null

        function updateHighlight() {
            var item = flickable.contentItem.childAt(mouseX + flickable.contentX, mouseY + flickable.contentY);
            if (item)
                item.color = "yellow";
            if (lastItem && item !== lastItem)
                lastItem.color = "white";
            lastItem = item;
        }

        onPositionChanged: updateHighlight()
    }
}

[jeremy_k]

Moving the MouseArea into the Repeater delegate and removing the timer's call to updateHighlight() in the above example also works as expected. This suggests that MouseArea is able to detect when a hover has ended due to the MouseArea moving, at least in this scenario.

[Dmitriano]

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

    function updateHighlight() {
        var item = flickable.contentItem.childAt(mouseX + flickable.contentX, mouseY + flickable.contentY);

it is not clear what to do with the item accessed with the code above, because this item is a QML control like Text, for example, but I need not a QML control, but the model bound to the table row. I access it with

var item = table.model.rowKey(index)

where rowKey(index) is an invokable method explicitly defined in my model, so I need to know item's index.

Also after doing some further testing, I noticed that CheckBox does not respond to clicks if the model is sorted dynamically, probably it uses MouseArea that stops working.

[jeremy_k]

@Dmitriano said in MouseArea works incorrectly inside TableView's delegate:

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

    function updateHighlight() {
        var item = flickable.contentItem.childAt(mouseX + flickable.contentX, mouseY + flickable.contentY);

it is not clear what to do with the item accessed with the code above, because this item is a QML control like Text, for example, but I need not a QML control, but the model bound to the table row. I access it with

var item = table.model.rowKey(index)

where rowKey(index) is an invokable method explicitly defined in my model, so I need to know item's index.

Use the properties of the item returned by childAt(). Color, index, etcetera.

[Dmitriano]

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

Use the properties of the item returned by childAt(). Color, index, etcetera.

some of my items has item property that I declare explicitly with a code like (index and other properties can be defined in the same way)

        delegate: DelegateChooser {
            role: "type"
            DelegateChoice {
                roleValue: "symbol"
                delegate: SymbolCell { item: model.item }
            }

see the screenshot

so theoretically, my clicking code can be transformed into this:

        MouseArea
        {
            id: ma
            anchors.fill: parent
            //hoverEnabled: true
            onClicked:
            {
                var item = table.contentItem.childAt(mouse.x, mouse.y);
                window.openMarket(item.item)
            }
        }

this also works with dynamically sorted model, but would require declaring item property explicitly in all the delegates that is a bit ugly overhead that prevents simple delegates (like a Text) from being simple.

Also, as I mentioned above, CheckBox does not respond to clicks with dynamically sorted model and I did not try other interactive controls yet.

And highlighting a row is still a task that we can't solve without an ugly overhead. For example, if the mouse is over an item (delegate) and I change its color I can't change it back when item's index is changed and the item is moved away.

[jeremy_k]

@Dmitriano said in MouseArea works incorrectly inside TableView's delegate:

@jeremy_k said in MouseArea works incorrectly inside TableView's delegate:

Use the properties of the item returned by childAt(). Color, index, etcetera.

some of my items has item property that I declare explicitly with a code like (index and other properties can be defined in the same way)

        delegate: DelegateChooser {
            role: "type"
            DelegateChoice {
                roleValue: "symbol"
                delegate: SymbolCell { item: model.item }
            }

see the screenshot

so theoretically, my clicking code can be transformed into this:

        MouseArea
        {
            id: ma
            anchors.fill: parent
            //hoverEnabled: true
            onClicked:
            {
                var item = table.contentItem.childAt(mouse.x, mouse.y);
                window.openMarket(item.item)
            }
        }

Be careful about validating that childAt() returned a usable item. The user may have clicked over blank space.

this also works with dynamically sorted model, but would require declaring item property explicitly in all the delegates that is a bit ugly overhead that prevents simple delegates (like a Text) from being simple.

Sure. This seems to be a view with some complication. Overlaying a MouseArea on the entire thing is avoiding one set of complications by selecting another.

Also, as I mentioned above, CheckBox does not respond to clicks with dynamically sorted model and I did not try other interactive controls yet.

If the CheckBox is in a delegate, setting
propagateComposedEvents on the overlay MouseArea may help.

And highlighting a row is still a task that we can't solve without an ugly overhead. For example, if the mouse is over an item (delegate) and I change its color I can't change it back when item's index is changed and the item is moved away.

That's what the lastItem property in https://forum.qt.io/post/621263 is for. Store identifying information for the next update and undo the changes when lastItem != current item. Or have a property that points to the selected row and have all others use the default color.

If you haven't already, have a look at ListView. The highlight delegate and currentIndex property might make more sense for this use. The QtQuick

[Dmitriano]

@jeremy_k Unfortunately, my MouseArea that covers the entire view and finds the delegate does not detect row insertion. For example on the picture below two rows surrounded with green were inserted (with beginInsertRows/endInsertRows) and MouseArea stopped responding to the clicks on the last two rows surrounded with red:

Below I provided the source code of the entire TableView as it is now in my project:

    TableView
    {
        id: table
        anchors.fill: parent
        columnSpacing: 5
        rowSpacing: 3
        clip: true

        property var columnWidths: [100, 80, 80, 20, 20, 20, 90, 90];
        columnWidthProvider: function (column) { return columnWidths[column]; }

        property var rowHeight: 40

        rowHeightProvider: function (column) { return rowHeight; }

        ScrollBar.horizontal: ScrollBar{}
        ScrollBar.vertical: ScrollBar{}
        ScrollIndicator.horizontal: ScrollIndicator { }
        ScrollIndicator.vertical: ScrollIndicator { }

        MouseArea
        {
            //id: ma
            anchors.fill: parent
            //hoverEnabled: true
            onClicked:
            {
                var index = Math.floor((mouse.y - table.originY) / (table.rowHeight + table.rowSpacing));
                console.log("index:", index, " mouse: (", mouse.x, "," , mouse.y, ") table.origin: (", table.originX, ",", table.originY + ") table.content: (", table.contentX, ",", table.contentY + ")")
                var item = table.model.rowKey(index)
                if (item)
                    window.openMarket(item)
            }
        }

        QtObject
        {
            id: enumSymbols
            property string spotAllowed: "S"
            property string marginAllowed: "M"
            property string isolatedMarginAllowed: "I"
        }

        delegate: DelegateChooser {
            role: "type"
            DelegateChoice {
                roleValue: "symbol"
                delegate: SymbolCell { item: model.item }
            }
            DelegateChoice {
                roleValue: "price"
                delegate: Text {
                    horizontalAlignment: Text.AlignRight
                    verticalAlignment: Text.AlignVCenter
                    text: { var val = model.item[model.name]; return val ? val.toFixed(model.item.pricePrecision) : ""; }
                }
            }
            DelegateChoice {
                roleValue: "signal"
                delegate: Text {
                    horizontalAlignment: Text.AlignRight
                    verticalAlignment: Text.AlignVCenter
                    text: TimeFormat.ago(model.item.signalTime, timeMachine.now)
                    color: model.item.signalTime ? "black" : "gray"
                }
            }
            DelegateChoice {
                roleValue: "enum"
                delegate: Text
                {
                    horizontalAlignment: Text.AlignHCenter
                    verticalAlignment: Text.AlignVCenter
                    text: model.display ? enumSymbols[model.name] : ""
                    color: "#1e73cd"
                }
            }
            DelegateChoice {
                roleValue: "zparams"
                delegate: Text
                {
                    property var zparams: model.item[model.name]
                    horizontalAlignment: Text.AlignRight
                    verticalAlignment: Text.AlignVCenter
                    text: zparams ? "(%1, %2, %3)".arg(zparams.lag).arg(zparams.threshold.toFixed(2)).arg(zparams.influence.toFixed(2)) : qsTr("No")
                    color: zparams ? "black" : "gray"
                }
            }
            DelegateChoice {
                roleValue: "check"
                delegate: CheckBox {
                    checked: model.item[model.name];
                    onClicked: {
                        table.model.beginUpdateItem(model.item)
                        model.item[model.name] = checked
                        table.model.endUpdateItem(model.item)
                    }
                }
            }
            DelegateChoice {
                delegate: Text {
                    verticalAlignment: Text.AlignVCenter
                    text: model.item[model.name]
                }
            }
        }
    }

If I refresh my TableView with beginResetModel/endResetModel MouseArea starts to work correctly.