使用QML LocalStorage来存储我们的数据

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickView>
#include <QDebug>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQuickView view;
    qDebug() << "Local storage path: " << view.engine()->offlineStoragePath();
    QObject::connect(view.engine(), SIGNAL(quit()), qApp, SLOT(quit()));

    view.setSource(QUrl(QStringLiteral("qrc:///Main.qml")));
    view.setResizeMode(QQuickView::SizeRootObjectToView);
    view.show();
    return app.exec();
}

Local storage path:  "/home/phablet/.local/share/localstorage/QML/OfflineStorage"

phablet@ubuntu-phablet:~/.local/share/localstorage.liu-xiao-guo/Databases$ ls
4ff10001f402923590ceb1d12a0cffc6.ini  4ff10001f402923590ceb1d12a0cffc6.sqlite

  QObject::connect(view.engine(), SIGNAL(quit()), qApp, SLOT(quit()));

对于本应用来说，我们希望在退出时得到一个事件来保存我们的设置。全部我们有这样一个特殊的处理。

.import QtQuick.LocalStorage 2.0 as Sql

var db;

function initDatabase() {
    print('initDatabase()')

    db = Sql.LocalStorage.openDatabaseSync("CrazyBox", "1.0", "A box who remembers its position", 100000);
    db.transaction( function(tx) {
        print('... create table')
        tx.executeSql('CREATE TABLE IF NOT EXISTS data(name TEXT, value TEXT)');
    });
}

function readData() {
    print('readData()')

    if(!db) { return; }
    db.transaction( function(tx) {
        print('... read crazy object')
        var result = tx.executeSql('select * from data where name="crazy"');
        if(result.rows.length === 1) {
            print('... update crazy geometry')
            // get the value column
            var value = result.rows[0].value;
            // convert to JS object
            var obj = JSON.parse(value)
            // apply to object
            crazy.x = obj.x;
            crazy.y = obj.y;
        }
    });
}

function storeData() {
    print('storeData()')

    if(!db) { return; }
    db.transaction( function(tx) {
        print('... check if a crazy object exists')
        var result = tx.executeSql('SELECT * from data where name = "crazy"');
        // prepare object to be stored as JSON
        var obj = { x: crazy.x, y: crazy.y };
        if(result.rows.length === 1) {// use update
            print('... crazy exists, update it')
            result = tx.executeSql('UPDATE data set value=? where name="crazy"', [JSON.stringify(obj)]);
        } else { // use insert
            print('... crazy does not exists, create it')
            result = tx.executeSql('INSERT INTO data VALUES (?,?
)', ['crazy', JSON.stringify(obj)]);
        }
    });
}

import QtQuick 2.0
import Ubuntu.Components 1.1
import "database.js" as DB

/*!
    \brief MainView with a Label and Button elements.
*/

MainView {
    // objectName for functional testing purposes (autopilot-qt5)
    objectName: "mainView"

    // Note! applicationName needs to match the "name" field of the click manifest
    applicationName: "localstorage.liu-xiao-guo"

    /*
     This property enables the application to change orientation
     when the device is rotated. The default is false.
    */
    //automaticOrientation: true

    // Removes the old toolbar and enables new features of the new header.
    useDeprecatedToolbar: false

    width: units.gu(60)
    height: units.gu(85)

    Page {
        title: i18n.tr("Localstorage")

        Rectangle {
            id: crazy
            objectName: 'crazy'
            width: 200
            height: 200
            x: 50
            y: 50
            color: "#53d769"
            border.color: Qt.lighter(color, 1.1)

            Text {
                anchors.centerIn: parent
                text: Math.round(parent.x) + '/' + Math.round(parent.y)
            }

            MouseArea {
                anchors.fill: parent
                drag.target: parent
            }
        }


        Component.onCompleted: {
            DB.initDatabase();

            print("it is going to read data");
            DB.readData();
        }

        Component.onDestruction: {
            print("it is going to save data");
            DB.storeData();
        }

        Button {
            anchors.bottom: parent.bottom
            anchors.bottomMargin: units.gu(1)
            anchors.horizontalCenter: parent.horizontalCenter
            text: "Close"
            onClicked: {
                Qt.quit();
            }
        }
    }
}

我们在UI被装载完后。初始化数据库，并读取已经存储的数据。假设数据已经存在，就读出来。并初始化我们的Rectangle “crazy”。

在应用退出的时候，我们存储我们的数据。这里应该注意的是，当我们用我们的手指拖动关掉应用时。我们的应用接受不到例如以下的事件：

        Component.onDestruction: {
            print("it is going to save data");
            DB.storeData();
        }