Rudi Grobler

This article demonstrates how to use the Windows Sensor and Location platform to dynamically change a applications theme based on the ambient light luminance intensity!

What we need

• Windows 7 Sensor Development Kit (Hardware and Software)
• Windows® API Code Pack for Microsoft® .NET Framework
• WPF Themes

Windows Sensor and Location platform

The Windows Sensor and Location platform, which is new for Windows 7, enables your computer and applications to adapt to their current environment. With location sensors -- including GPS devices, WWAN radios, and even triangulation technology -- your applications and gadgets can know exactly where they are, enabling them to provide more locally relevant content and functionality. Ambient light sensors, for example, can allow your computer to automatically adjust your screen's brightness based on the current lighting conditions. They can also enable applications to optimize their content for readability, making your computer more useful in a range of operating environments than ever before.

The platform provides a standard way to integrate sensor and location devices into Windows, as well as a standard programming interface for applications to take advantage of these devices. On Windows 7, the user has control over how data from these devices is exposed to applications. Hardware manufacturers can learn how to write sensor and location drivers by installing the Windows 7 WDK. Developers can learn how to write location-aware and sensor-enabled applications by installing the Windows 7 SDK.

The Basics

The Windows 7 Sensor Development Kit is equipped with a ambient light sensor! To read the current ambient light luminance intensity, we will use the Windows® API Code Pack for Microsoft® .NET Framework…

First, we need to find all the ambient light sensor available and then set it to automatically poll for new data reports

SensorList<AmbientLightSensor> als = SensorManager.GetSensorsByTypeId<AmbientLightSensor>();
foreach (var sensor in als)
{
    sensor.AutoUpdateDataReport = true;
    sensor.ReportInterval = 10;
    sensor.DataReportChanged += new DataReportChangedEventHandler(sensor_DataReportChanged);
}

All that is left to do then is to use the data report!

void sensor_DataReportChanged(Sensor sender, EventArgs e)
{
    AmbientLightSensor als = sender as AmbientLightSensor;

    // Read the als.CurrentLuminousIntensity.Intensity... 0~200            
}

And that is it!

Why should I care?

Imagine the following scenario: I have a application which has a normal theme and a high contrast theme for when there is direct sunlight and I want to switch between these based on the luminance intensity from the sensors?

For this scenario I took the WPF themes and extended the theme manager to support

Using the basics we just looked at and the magic off attached behaviors, this is how you would then use it

<Window x:Class="WPF.Themes.Demo.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:themes="clr-namespace:WPF.Themes;assembly=WPF.Themes">
    <themes:ThemeManager.ThemeSelector>
        <themes:AmbiendLighThemeSelector NormalTheme="ExpressionDark" HighContrastTheme="ExpressionLight" />
    </themes:ThemeManager.ThemeSelector>

    <!-- Add your UI stuff here... -->

</Window>

This is also easily portable to the Blend SDK behaviors!

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