TypeError: Cannot read property 'length' of undefined in QML array

[TheIndependentAquarius]

Alias.qml

import QtQuick 2.0
 
Rectangle {
    width: 100
    height: 62
 
    property var arr : [1,2,3,4]
}

import QtQuick 2.0

Rectangle {
    width: 100
    height: 62

    property var arr : [1,2,3,4]
}

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Access.qml

import QtQuick 2.0
 
Rectangle {
    id: newq
 
    width: 100
    height: 62
 
    property var yy : [1]
    property var pp : [1]
 
    onPpChanged:
    {
        console.log("\npp: " +  pp.pop())
        console.log("\nyy: " + newq.yy.length + "\n")
    }
}

import QtQuick 2.0

Rectangle {
    id: newq

    width: 100
    height: 62

    property var yy : [1]
    property var pp : [1]

    onPpChanged:
    {
        console.log("\npp: " +  pp.pop())
        console.log("\nyy: " + newq.yy.length + "\n")
    }
}

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main.qml

import QtQuick 2.0
 
Rectangle {
    id: root
    width: 360
    height: 360
 
    Alias
    {
        id: poi
    }
 
    Access
    {
        pp: poi.arr
    }
}

import QtQuick 2.0

Rectangle {
    id: root
    width: 360
    height: 360

    Alias
    {
        id: poi
    }

    Access
    {
        pp: poi.arr
    }
}

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The error shows up on this line:

console.log("\nyy: " + newq.yy.length + "\n")

console.log("\nyy: " + newq.yy.length + "\n")

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Where am I going wrong?

[anda_skoa]

Do you also get that when you run just Access.qml?
Have you tried without "newq"? You don't use that for access to "pp".

Cheers,
_

[TheIndependentAquarius]

Do you also get that when you run just Access.qml?

The error appears only when I access and thus assign the property of Access.qml in main.qml.

Have you tried without "newq"? You don't use that for access to "pp".

A drowning person grabs a straw. I tried newq because the original way wasn't working - I know it is not needed.

Would you please try the code on your machine (if you have it nearby)?

Thanks.

[anda_skoa]

The yy property is just not set yet when pp gets changed.

If you add a onYyChanged handler you'll see that it gets set after the other one.

So it is still undefined when the first change handler is invoked.

Cheers,
_

[TheIndependentAquarius]

thankful to you, got the point now.

[wysota]

In situations such as this it is wise to use a Component.onCompleted handler to make sure the other method only gets executed when the object is fully constructed:

Item {
  property var prop
  property var prop2
 
  property bool __constructed: false
 
  onPropChanged: {
    if(!__constructed) return
    doSomethingWith(prop2)
  }
  Component.onCompleted: {
    __constructed = true
    // do some other initial stuff
  }
}

Item {
  property var prop
  property var prop2

  property bool __constructed: false

  onPropChanged: {
    if(!__constructed) return
    doSomethingWith(prop2)
  }
  Component.onCompleted: {
    __constructed = true
    // do some other initial stuff
  }
}

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[TheIndependentAquarius]

wysota

That was very helpful - much thankful to you too.