QML Progress Bar doesn't move - qt

Question

I am using QT v5.12.6 and in my application i am planning to use Progress Bar during application bootup for around 15secs. In this 15secs operations like:
QML components creation.
connection with the server.
Other bootup operations will be running in the background.
Once, all the bootup operation is done i will hide my splash screen which is just a Rectangle which includes Loading text with a progress bar. For this 15 secs i will be incrementing the progress bar but the progress bar doesn't increment/move for some 10 secs. It looks like it is hanged, but if i use a busy indicator it starts to rotate. Unfortunately, i can't use busy indicator component as i need a look and feel like a progress bar.
My application runs on a embedded platform which has low end processor and very less RAM speed. I am assuming this problem is due to the Load on the UI as many components is getting created.
Is there any difference between busy indicator and Progress bar and also any suggestions on how to handle UI load on the bootup ?
Edit 1: Added an example. I have tried my level best to mimic the problem. In this example both the busyindicator and Progress bar is getting stuck for sometime. But in the embedded device Busy indicator works but no idea how. After running the application Please click on Click Me button.
import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.3
Window {
property int pbValue:0
visible: true
width: 500
height: 400
title: qsTr("Hello World")
Rectangle{
id: mySplashScreen
anchors.fill: parent
ProgressBar{
id: pBar
height: 20
width: parent.width
anchors.bottom: parent.bottom
from:0
value : pbValue
to:30
}
BusyIndicator{
anchors.right: parent.right
running: (pbValue < pBar.to +1)
}
Button{
text: "click me"
onClicked: {
//Create component equivalent to my application which has "n"
//number of components like buttons, combobox, chart view etc.
//Here just creating the rectangle more number of times.
for(var i = 0 ; i < 15000 ;i++) //HINT : Increase/decrease the value if problem is not seen
{
var comp = mycomp.createObject(mySplashScreen)
}
}
}
}
Timer{
id:timer
interval: 250
running: (pbValue < pBar.to +1)
onTriggered: {
pbValue += 1;
}
}
Component{
id:mycomp
Rectangle{
width: 200
height: 200
color: "green"
}
}
}

Answer 1

Move your object creation code into a separate Timer with a small interval, and rather than creating all of the objects at once, create them maybe 50 at a time every 25 MS or something.
This will allow for the main event loop to process other things like the animations for busy indicator while its loading.
Here's one way to go about implementing this
import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.3
Window {
property int pbValue: 0
visible: true
width: 500
height: 400
title: qsTr("Hello World")
Rectangle {
id: mySplashScreen
anchors.fill: parent
ProgressBar {
// changed handling of progress bar
id: pBar
height: 20
width: parent.width
anchors.bottom: parent.bottom
from: 0
value: compList.length // bind this value
to: 15000
}
BusyIndicator {
anchors.right: parent.right
running: (pbValue < pBar.to + 1)
}
Button {
text: "click me"
onClicked: {
timer.running = true
}
}
}
property var compList: [] // created property to store all created components to track what has been done
Timer {
id: timer
interval: 25
running: false
repeat: true
onTriggered: {
for (var i = 0; i < 50; i++) {
var comp = mycomp.createObject(mySplashScreen) // moved component into timer
compList.push(comp) // added component to huge list of components for tracking
}
pbValue = compList.length
if ((pbValue >= 15000)) {
timer.running = false
console.log("All components completed")
}
}
}
Component {
id: mycomp
Rectangle {
width: 200
height: 200
color: "green"
}
}
}