Displaying a Large PDF without Freezing the UI Thread

Serhan Kars

Hi everyone,

I am having some problems displaying a large PDF file using a Loader. I have a sample code below:

When the Load button is pressed in the code below, a large PDF file is displayed using PdfMultiPageView. I also make an AnimatedImage visible when the Loader is loading the component. However, since the PDF is a large file, the UI thread probably freezes when creating the PDF elements.

Do you have any suggestions for cases like this?

I am aware that using Qt.callLater is useful for operations with loops that take a long time, but this case is a little bit different.

Thanks in advance.

import QtQuick
import QtQuick.Pdf
import QtQuick.Controls

Window {
    width: 500
    height: 500

    visible: true
    title: "PdfTest"

    Rectangle {
        anchors.fill:parent

        Loader{
            id: loader
            anchors.fill: parent
            asynchronous: true
            sourceComponent: undefined
            onLoaded: loadingImg.visible = false
        }

        Component{
            id: pmvComp
            PdfMultiPageView{
                document: PdfDocument{ source: 'LARGE_PDF_FILE.pdf'} // some Pdf with 20 MB size
            }
        }

        AnimatedImage {
            id: loadingImg
            anchors.centerIn: parent
            source: "loading.gif"
            width:50
            height:50
            visible:false
        }

        Button{
            anchors.horizontalCenter: parent.horizontalCenter
            anchors.bottom: parent.bottom
            anchors.bottomMargin: 10

            text: loader.sourceComponent == undefined ?  "Load":"Unload"
            onClicked: {

                    if(loader.sourceComponent == undefined){
                        loadingImg.visible = true
                        loader.sourceComponent = pmvComp
                    }
                    else{
                        loader.sourceComponent = undefined
                    }
            }
        }
    }

}