QML : Navigation between qml pages from design perception

Question

We need to develop a QtQuick project, where we have about 100 screens.

I had tried to make a demo project for the navigation which has three screens on button click. I had used the concepts of 'States' in the navigation between the pages. Initially I tried the same using 'Loader' but loader was not able to retain the previous state of page, it was re-loading the entire page during the navigation.

Below is the code snippet of main.qml

// import QtQuick 1.0 // to target S60 5th Edition or Maemo 5
import QtQuick 1.1

Rectangle {
    id:main_rectangle
    width: 360
    height: 640

    Page1{
        id:page1
    }

    Page2{
        id:page2
    }

    Page3{
        id:page3
    }

    states: [
        State {

            name: "page2"

            PropertyChanges { target: page3; visible:false; }
            PropertyChanges { target: page1; visible:false; }
            PropertyChanges { target: page2; visible:true; }
        },
        State {
            name: "page1"
            PropertyChanges { target: page3; visible:false; }
            PropertyChanges { target: page2; visible:false; }
            PropertyChanges { target: page1; visible:true; }
        },

        State {
            name: "page3"
            PropertyChanges { target: page1; visible:false; }
            PropertyChanges { target: page2; visible:false; }
            PropertyChanges { target: page3; visible:true; }
        }

    ]

}

This runs well with the small POC with three screens, but its not feasible to define states for 100 screens.

From designing aspect we concluded to make a C++ controller we controls the states, visibility of various pages.

Need suggestions how to implement the 'State' logic in C++.

Answer 1

Here is the simplest solution in plain QML, using a configurable page list (like a model) + a Repeater + Loader items to not load everything at startup (lazy instanciation) and not destroy a page after hiding it (to not have to reload it if we come back to it) :

import QtQuick 1.1

Rectangle {
    id: main_rectangle;
    width: 360;
    height: 640;

    // Put the name of the QML files containing your pages (without the '.qml')
    property variant pagesList  : [
        "Page1",
        "Page2",
        "Page3",
        "Page4",
        "Page5"
    ];

    // Set this property to another file name to change page
    property string  currentPage : "Page1";

    Repeater {
        model: pagesList;
        delegate: Loader {
            active: false;
            asynchronous: true;
            anchors.fill: parent;
            visible: (currentPage === modelData);
            source: "%1.qml".arg(modelData)
            onVisibleChanged:      { loadIfNotLoaded(); }
            Component.onCompleted: { loadIfNotLoaded(); }

            function loadIfNotLoaded () {
                // to load the file at first show
                if (visible && !active) {
                    active = true;
                }
            }
        }
    }
}

Hope it helps !