Pragma singleton inside QML doesnt works for me

[vladstelmahovsky]

Hi

I'm trying to use new QML feature: pragma Sigleton
but when use the singleton item, Qt always claim: ReferenceError: <Item> is not defined
here is singletone item's code:
SysPref.qml
@pragma Singleton
import QtQuick 2.2
import QtQuick.Window 2.1

QtObject {
property int itemSizeLarge: 16//Screen.logicalPixelDensity * 16
property int itemSizeMedium: 10//Screen.logicalPixelDensity * 10
property int itemSizeSmall: 8//Screen.logicalPixelDensity * 8
}@

trying to access to it:

@console.log("item size large:", SysPref.itemSizeLarge)@

and got mentioned error
my bug ot Qt's or is it still not implemented?
Qt latest stable branch

[vladstelmahovsky]

ok, digging git commits of qtdeclarative, I've found missed part:
Usage:
// First, define your QML singleton type which provides the functionality.
@pragma Singleton
import QtQuick 2.0
Item {
property int testProp1: 125
}
@
// Second, register the QML singleton type by calling this function in an initialization function.
@#include <QtQml>
...
qmlRegisterSingletonType(QUrl("file:///absolute/path/SingletonType.qml"), "Qt.example.qobjectSingleton", 1, 0, "RegisteredSingleton");
@
In order to use the registered singleton type in QML, you must import the singleton type.
@
import QtQuick 2.0
import Qt.example.qobjectSingleton 1.0
Item {
id: root
property int someValue: RegisteredSingleton.testProp1
}@

[Maheshdev305]

Hi, I tried your example,
for me it gives the following error during compilation.!

bq. error: C2664: 'int qmlRegisterSingletonType(const char *,int,int,const char *,QJSValue (__cdecl *)(QQmlEngine *,QJSEngine *))' : cannot convert parameter 2 from 'const char [7]' to 'int'
There is no context in which this conversion is possible

am using Qt 5.1. please help.

[vladstelmahovsky]

Hi

Probably you have to use Qt 5.2 and later

[SteveG]

Try the following. The order is unimportant.

1. Create QML file (e.g., Test.qml) that uses singleton and add to your .qrc file
2. Create MySingletonDir subdirectory
3. Create singleton QML file (e.g., MySingleton.qml) in MySingletonDir
4. Specify
   @
   pragma Singleton
   @

at top of MySingleton.qml
5. Add qmldir file in same directory as MySingleton.qml with content
@
singleton MySingleton 1.0 MySingleton.qml
@

6. Add MySingleton.qml and qmldir to your .qrc file
7. Add
   @
   import "MySingletonDir" 1.0
   @

to Test.qml
8. Reference singleton in Test.qml (e.g., MySingleton.myProperty)

Nothing is required in any C++ file.

[Mahaboobsab]

Hi SteveG

I tried the same method you said. the singleton is working fine all the places except inside the states.

example
states:[
State
{
name: "HitState"

            PropertyChanges
            {
                target: gradientMainColor
                color: single.button_hitstate_color
            }

            PropertyChanges
            {
                target: gradientMainColor1
                color: single.button_hitstate_color
        }
    ]

the error message is single undefined

[SteveG]

Mahaboobsab,

Is single your singleton and does it have a button_hitstate_color property? How do you reference the singleton in other parts of your code?

[Mahaboobsab]

Hi SteveG

Yes single is my singleton and button_hitstate_color is one of the property in MySingleton.qml

Inisde qmldir i have created the module names Styles with version 1.0
singleton single 1.0 MySingleton.qml

where ever i need this i include module import Styles 1.0
and start using the single.property ... it works fine for all the places in the any qml file except inisde the states i,e property changes

[SteveG]

Mahaboobsab,

As a possible workaround (i.e., hack), does it work if you define
@
property color my_button_hitstate_color: single.button_hitstate_color
@

and reference my_button_hitstate_color in PropertyChanges?

Regardless,you may want to file a bug report. It would be helpful to attach zipped sample files with a singleton, a qmldir file and a QML component that shows the singleton not working in PropertyChanges but working other places.

[Mahaboobsab]

Hi SteveG,

singleton single 1.0 MySingleton.qml

it worked by giving first letter of singleton name in Caps as "Single"

i am wondering how its related to name ..if it is qml file name it has to be in Caps but singleton name.

[Mahaboobsab]

Hi Steveg

I am using singleton but facing problem if i use more than 2 singleton in one qmldir .
can u comment on this.?