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I have dynamically created some QML rectangles on a Canvas. I wish to toggle whether the rectangles can be dragged around or not via the drag.target property, which is declared upon creation inside MouseArea. If the rectangles are draggable, I set drag.target to "parent". If not, I set it to "undefined".

The rectangles are stored in an array called verts[]. When I try to access the drag.target property, I get an error: TypeError: Value is undefined and could not be converted to an object

Here is the function that produces the error. I am feeding it an array of rectangles (verts) and a boolean.

function setVertsDraggable(verts, draggable) {
    for (var i=0; i<verts.length; i++) {
        if (draggable) {
            verts[i].drag.target = "parent";
        }
        else {
            verts[i].drag.target = "undefined";
        }
    }
}

I have tried feeding it the values of "parent" and "undefined" in quotes, without quotes, by setting another variable to undefined and passing that variable, and an empty string. Perhaps there are values defined in QML somewhere, such as QtQuick.(SomeClassOfEnums).undefined

But I suspect that the bigger problem is that it is not recognizing vert[i].drag.target as a property. Perhaps my path is wrong. I have tried

vert[i].drag.target
vert[i].MouseArea.drag.target
vert[i].Rectangle.MouseArea.drag.target
vert[i].Rectangle.drag.target

Additionally, I am able to set the color of those rectangles via javascript. The same syntax allows me to set the color without any error:

function setVertsColor(verts, color) {
    for (var i=0;i<verts.length; i++) {
        verts[i].color = color;
    }
}

So if this syntax works with color, what is the problem with the drag.target property?

If it helps, here is the command I use to dynamically create the rectangles:

var component = Qt.createComponent("Vertex.qml");
var vertex = component.createObject(parent, {x: xPos, y: yPos, width: size, color:"yellow"});

And here is the Vertex.qml which contains the definition of the rectangles, called by component.createObject(...)

import QtQuick

Rectangle {
    width: 8
    height: 8
    color: yellow
    property string tag: ""
    MouseArea {
        anchors.fill: parent
        drag.target: undefined
        drag.smoothed: false
        onReleased: {
            polyCanvas.requestPaint()
        }
    }
}

Please let me know if you have any ideas. I'm fresh out of 'em.

I have dynamically created some QML rectangles on a Canvas. I wish to toggle whether the rectangles can be dragged around or not via the drag.target property, which is declared upon creation inside MouseArea. If the rectangles are draggable, I set drag.target to "parent". If not, I set it to "undefined".

The rectangles are stored in an array called verts[]. When I try to access the drag.target property, I get an error: TypeError: Value is undefined and could not be converted to an object

Here is the function that produces the error. I am feeding it an array of rectangles (verts) and a boolean.

function setVertsDraggable(verts, draggable) {
    for (var i=0; i<verts.length; i++) {
        if (draggable) {
            verts[i].drag.target = "parent";
        }
        else {
            verts[i].drag.target = "undefined";
        }
    }
}

I have tried feeding it the values of "parent" and "undefined" in quotes, without quotes, by setting another variable to undefined and passing that variable, and an empty string. Perhaps there are values defined in QML somewhere, such as QtQuick.(SomeClassOfEnums).undefined

But I suspect that the bigger problem is that it is not recognizing vert[i].drag.target as a property. Perhaps my path is wrong. I have tried

vert[i].drag.target
vert[i].MouseArea.drag.target
vert[i].Rectangle.MouseArea.drag.target
vert[i].Rectangle.drag.target

Additionally, I am able to set the color of those rectangles via javascript. The same syntax allows me to set the color without any error:

function setVertsColor(verts, color) {
    for (var i=0;i<verts.length; i++) {
        verts[i].color = color;
    }
}

So if this syntax works with color, what is the problem with the drag.target property?

If it helps, here is the command I use to dynamically create the rectangles:

var component = Qt.createComponent("Vertex.qml");
var vertex = component.createObject(parent, {x: xPos, y: yPos, width: size, color:"yellow"});

And here is the Vertex.qml which contains the definition of the rectangles, called by component.createObject(...)

import QtQuick

Rectangle {
    width: 8
    height: 8
    color: yellow
    property string tag: ""
    MouseArea {
        anchors.fill: parent
        drag.target: undefined
        drag.smoothed: false
        onReleased: {
            polyCanvas.requestPaint()
        }
    }
}

Please let me know if you have any ideas. I'm fresh out of 'em.

• qt
• qml
• draggable
• qqmlcomponent

Share Improve this question Follow edited Apr 1 at 23:29 eyllanesc 245k1919 gold badges201201 silver badges280280 bronze badges asked Mar 28 at 0:09 brianscbriansc 322 bronze badges

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1 Answer 1

Sorted by: Reset to default 0

You can use a delegate/model to dynamically create and destroy components. You can also replace MouseArea with a DragHandler and TapHandler. By adding dragEnabled to your model we can control runtime dragability via property binding:

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts
Page {
    property list<var> pts: []
    Repeater {
        model: pts
        delegate: Vertex {
            x: modelData.x
            y: modelData.y
            dragEnabled: modelData.dragEnabled
        }
    }
    function addRandom(n) {
        do {
            let x = Math.floor(Math.random() * 300);
            let y = Math.floor(Math.random() * 300);
            let dragEnabled = Math.random() >= 0.5;
            pts.push( {x,y,dragEnabled} );
        } while (--n > 0);
    }
    Component.onCompleted: addRandom(3)
    footer: Frame {
        RowLayout {
            Button { text: "Clear"; onClicked: pts.length = 0 }
            Button { text: "Add 1"; onClicked: addRandom() }
            Button { text: "Add 10"; onClicked: addRandom(10) }
        }
    }
}

// Vertex.qml
import QtQuick
import QtQuick.Controls
Rectangle {
    width: 16
    height: 16
    color: dragEnabled ? "green" : "red"
    property bool dragEnabled: true
    DragHandler { enabled: dragEnabled }
    TapHandler { onTapped: dragEnabled = !dragEnabled }
}

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