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Reply
New Contributor
Posts: 6
Registered: ‎12-23-2012
My Device: Playbook 2.0
My Carrier: MegaFon RUS
Accepted Solution

Qml perfomance

Hello. I have a problem with qt on playbook. I have successfully created a simple reader for PB, using qml technology, but when I scroll text, I have annoying lags. I have taken a video of that: http://youtu.be/FW0JkUR4rQA

The elemnt, which is lagging, is a flickable element with custom rectanges inside it. There is a code:


 

    Flickable {
        property int myBottomMargin: 0
            id: flick
            anchors.rightMargin: 0
            anchors.bottomMargin: myBottomMargin
            anchors.leftMargin: 250
            anchors.topMargin: 48
            z: 1
            flickableDirection: Flickable.VerticalFlick
            contentWidth: 517
            contentHeight: 0
            interactive: true
            clip: true
            anchors.fill: parent
    }

 


 

 

Objects that are in it use that class:

import QtQuick 1.1


Rectangle {
    id: story
    property alias storyText : joke.text
    property alias idText : id.text
    property alias dateText : date.text
    property alias ratioText : ratio.text
    //transformOrigin: Item.TopLeft
    width: topLine.width
    height: topLine.height + border_image1.height

    Image {
        id: topLine
        x: 0
        y: 0
        source: "../quite_top.png"

        Image {
            id: image1
            x: 20
            y: 4
            width: 21
            height: 18
            source: "../up.png"
        }

        BorderImage {
            id: border_image1
            x: 0
            y: topLine.height + topLine.y
            width: topLine.width
            height: joke.paintedHeight
            border.top: 0
            border.right: 633
            border.left: 633
            z: -1
            source: "../quite_middle.png"
        }

        Text {
            id: joke
            x: 20
            y: topLine.height + topLine.y
            //+topLine.width*0.05
            width: border_image1.width-40
            height: 200
            font.family: "Times New Roman"
            //text: qsTr("good joke")
            wrapMode: Text.WrapAtWordBoundaryOrAnywhere
            font.pixelSize: 18
        }

        Image {
            id: bottomLine
            x: 0
            y: joke.paintedHeight + joke.y
            source: "../quite_bottom.png"
        }

        Text {
            id: id
            x: 497
            y: 6
            width: 116
            height: 14
            text: qsTr("")
            verticalAlignment: Text.AlignVCenter
            horizontalAlignment: Text.AlignRight
            font.pixelSize: 12
        }

        Text {
            id: date
            x: 327
            y: 6
            text: qsTr("")
            verticalAlignment: Text.AlignVCenter
            font.pixelSize: 12
        }

        Text {
            id: ratio
            x: 49
            y: 6
            text: qsTr("")
            verticalAlignment: Text.AlignVCenter
            horizontalAlignment: Text.AlignLeft
            font.pixelSize: 12
        }

    }
}

 


 

And how I full the list:

function addObjects() {
    console.log("Add objects")
    console.log(data[0][0])

    setStatusBarText();

    isLoading = false

    count = data[0].length

    var component = Qt.createComponent("Story.qml")
    var height_flick = y_offset

    //console.log(data[0][0]);
    for (var i=0;i<count;i++) {
        objects[i] = component.createObject(flick.contentItem, {
                                                    "x": x_offset,
                                                    "y": 0
                                            });
        if (i!=0) {
            objects[i].y = height_flick+objects[i-1].height + y_offset;
            height_flick = objects[i].y
        }
        objects[i].storyText = data[0][i]
        objects[i].idText = data[1][i]
        objects[i].ratioText = data[2][i]
        objects[i].dateText = data[3][i]
    }

    //console.log("min_value ",data[4])
    if (data[4]) {
        slider_page.min_value = data[4]
        slider_page.max_value = 1
    }

    flick.contentHeight = objects[count-1].y+objects[count-1].height + y_offset;

}

 

I use Qt 4.8.3 with default settings if it is matter. Thanks

 

Developer
Posts: 1,524
Registered: ‎12-18-2012
My Device: Z30, Z10 LE, DevAlpha C, PlayBook

Re: Qml perfomance

Hi,

Flickable isn't optimized for displaying many elements.

It's better to use a ListView with delegate & dataModel. ListView creates only the elements which are currently on screen and should work very fast.

Andrey Fidrya, @zmeyc on twitter
New Contributor
Posts: 6
Registered: ‎12-23-2012
My Device: Playbook 2.0
My Carrier: MegaFon RUS

Re: Qml perfomance

I thought about that, but as I know, ListView shows elements with constant height, but my elements in the list can range in height.
Highlighted
Developer
Posts: 1,524
Registered: ‎12-18-2012
My Device: Z30, Z10 LE, DevAlpha C, PlayBook

Re: Qml perfomance

I've created a test project and it seems that ListView can have elements of varying height. Haven't tried this with Qt Quick 1.0, but I guess it should work too.

 

 

import QtQuick 2.0

Rectangle {
    width: 1024
    height: 768

    ListModel {
        id: model1

        ListElement {
            elementColor: "red"
            elementHeight: 50
        }
        ListElement {
            elementColor: "green"
            elementHeight: 100
        }
        ListElement {
            elementColor: "blue"
            elementHeight: 30
        }
    }
    ListView {
        anchors.fill: parent

        model: model1
        delegate: Component {
            Rectangle {
                color: elementColor
                width: 100
                height: elementHeight
                Text {
                    text: elementColor
                }
            }
        }
    }
}

 


Andrey Fidrya, @zmeyc on twitter