One single instance of a qml component used in all other qml files

MHermann

Hello!

How is it possbile to create one single instance of a qml component (for example MyGlobalMessageBox.qml) and use this one instance in all other qml files?

Kind regards,
MHermann

sierdzio

Declare it as singleton in C++ or QML (also some info here).

Tirupathi Korla

@MHermann
Create a instance with id in main.qml and use that id in other files.
eg.

in main.qml..

MyGlobalMessageBox{
   id: mGlobalMB
   ......
}

In other file

mGlobalMB.property = xyz
or
mGlobalMB.functionCall()

MHermann

@sierdzio : Thanks for your answer.

Now I have done the following:

qmldir:

singleton Msgbox 1.0 qrc:/QML/Vetron_MessageBox.qml

MyGlobalMessageBox.qml:

pragma Singleton
import QtQuick 2.0
import QtQuick.Controls 2.2
import QtQuick.Layouts 1.3
import "."

Rectangle {
...
}

Now a get the following runtime errors:

QQmlApplicationEngine failed to load component
qrc:/QML/DataHandler.qml:-1 Type Msgbox unavailable
qrc:/QML/MyGlobalMessageBox.qml:-1 Msgbox is instantiated recursively

At the moment I am not using Msgbox in the programm.
What could be the reason for these errors?

sierdzio

I think you don't need the qmldir, just the pragma declaration, but maybe I am mistaken. Also I don't think qmldir supports QRC paths, it should be a plain path instead.

MHermann

@Tirupathi-Korla : Thanks for your answer.
From my "main.qml" I am creating the sub-components dynamically.
Therefore I can not access the ids of the "main.qml" or I don't know how to do that ...

MHermann

@sierdzio : Ok. And how can I access the MessageBox? Only via it's name?

MyGlobalMessageBox.x = ...
...

And if am using it this way in different qml files I will always use the same instance of the MessageBox?

sierdzio

Yes, it should be accessible via file name and point always to the same instance.

Tirupathi Korla

@MHermann
As you want it as a single instance, you may create in main.qml without creating it dynamically as

MyGlobalMessageBox{
   id: mGlobalMB
   ......
}

with which you can access it in other qml files using its id.

MHermann

@sierdzio : Ok. At the moment I am getting no errors. The code in MyGlobalMessageBox.qml is called. But the messagebox is not shown... Maybe it is because the parent of the messagebox is null. How can I resolve this problem?

MHermann

@Tirupathi-Korla : Ok. I did it like you recommended.

Main.qml:

Page {
   id: mainId

    MyGlobalMessageBox {
        id: myGlobMsgBox
    }

    Rectangle {
    ...
    GridLayout {
        ...

But I get "ReferenceError: myGlobMsgBox is not defined" when I try to access myGlobMsgBox in an other qml file. As I said before maybe it is because all other components are created dynamically in Main.qml. And it these other qml files I can not acces myGlobMsgBox neither mainId.

Tirupathi Korla

@MHermann
May i Know whats Page?? and is Page inside any ApplicationWindow?? and what ever you create dynamically are inside Page.. Right!!!!

And Vetron_MessageBox is a qml file.. right!!!

MHermann

@Tirupathi-Korla :
Page is loaded by a Loader in SwipeView in my MainPageManagement.qml. And this SwipeView is contained in an ApplicationWindow.
Yes. All dynamically created qml components are inside page.
I corrected my post before. I meant MyGlobalMessageBox...

Tirupathi Korla

@MHermann
Then better create Vetron_MessageBox inside ApplicationWindow.. so that it can be visible to all files..

MHermann

@Tirupathi-Korla : Now I changed some things in my structure.
Now I can access myGlobMsgBox and the message box is working.