Qml F1 Legends

This application demonstrates how to use XmlListModel as a datasource for a Chart.

Article lu fois.

L'auteur

The Qt Company Ltd.

L'article

Publié le 27 décembre 2024 - Mis à jour le 27 décembre 2024

Liens sociaux

Qml F1 Legends▲

Running the Example▲

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

Using List Models as Data Sources▲

Let's define an empty ChartView first:

Sélectionnez

ChartView {
    id: chartView
    title: "Driver Speeds, lap 1"
    anchors.fill: parent
    legend.alignment: Qt.AlignTop
    animationOptions: ChartView.SeriesAnimations
    antialiasing: true
}

Our XmlListModel uses hard-coded test data. In a real application the data source would be a timing system.

Sélectionnez

XmlListModel {
    // Hard-coded test data
    xml: "&lt;results&gt;&lt;row&gt;&lt;speedTrap&gt;0&lt;/speedTrap&gt;&lt;driver&gt;Fittipaldi&lt;/driver&gt;&lt;speed&gt;104.12&lt;/speed&gt;&lt;/row&gt;"
        +"&lt;row&gt;&lt;speedTrap&gt;0&lt;/speedTrap&gt;&lt;driver&gt;Stewart&lt;/driver&gt;&lt;speed&gt;106.12&lt;/speed&gt;&lt;/row&gt;"
        +"&lt;row&gt;&lt;speedTrap&gt;0&lt;/speedTrap&gt;&lt;driver&gt;Hunt&lt;/driver&gt;&lt;speed&gt;106.12&lt;/speed&gt;&lt;/row&gt;"
    ...
    query: "/results/row"

    XmlRole { name: "speedTrap"; query: "speedTrap/string()" }
    XmlRole { name: "driver"; query: "driver/string()" }
    XmlRole { name: "speed"; query: "speed/string()" }
}
// An example XmlListModel containing F1 legend drivers' speeds at speed traps
SpeedsXml {
    id: speedsXml
    onStatusChanged: {
        if (status == XmlListModel.Ready) {
            timer.start();
        }
    }
}

The data is parsed with a timer. The line series representing each driver are created on the fly.

Sélectionnez

// A timer to mimic refreshing the data dynamically
Timer {
    id: timer
    interval: 700
    repeat: true
    triggeredOnStart: true
    running: false
    onTriggered: {
        currentIndex++;
        if (currentIndex &lt; speedsXml.count) {
            // Check if there is a series for the data already
            // (we are using driver name to identify series)
            var lineSeries = chartView.series(speedsXml.get(currentIndex).driver);
            if (!lineSeries) {
                lineSeries = chartView.createSeries(ChartView.SeriesTypeLine,
                                                    speedsXml.get(currentIndex).driver);
                chartView.axisY().min = 0;
                chartView.axisY().max = 250;
                chartView.axisY().tickCount = 6;
                chartView.axisY().titleText = "speed (kph)";
                chartView.axisX().titleText = "speed trap";
                chartView.axisX().labelFormat = "%.0f";
            }
            lineSeries.append(speedsXml.get(currentIndex).speedTrap,
                              speedsXml.get(currentIndex).speed);

            if (speedsXml.get(currentIndex).speedTrap &gt; 3) {
                chartView.axisX().max = Number(speedsXml.get(currentIndex).speedTrap) + 1;
                chartView.axisX().min = chartView.axisX().max - 5;
            } else {
                chartView.axisX().max = 5;
                chartView.axisX().min = 0;
            }
            chartView.axisX().tickCount = chartView.axisX().max - chartView.axisX().min + 1;
        } else {
            // No more data, change x-axis range to show all the data
            timer.stop();
            chartView.animationOptions = ChartView.AllAnimations;
            chartView.axisX().min = 0;
            chartView.axisX().max = speedsXml.get(currentIndex - 1).speedTrap;
        }
    }
}

Example project▲

Example project @ code.qt.io

Vous avez aimé ce tutoriel ? Alors partagez-le en cliquant sur les boutons suivants :