Language: HTML | XAML

Quickstart: Responding to changes in lighting (C#)

Applies to Windows and Windows Phone

You can use the ambient light sensor to detect changes in lighting with an app written in C#.

An ambient light sensor is one of several types of environmental sensors that allow apps to respond to changes in the user's environment.

Roadmap: How does this topic relate to others? See: Roadmap for Windows Runtime apps using C# or Visual Basic.

The Windows.Devices.Sensors namespace includes support for a LightSensor object that apps can use to retrieve the current illuminance as a LUX value. For more information about LUX values, refer to the Sensor API documentation on MSDN.

Objective: After completing this quickstart you will understand how to use the light sensor to detect changes in lighting.

Prerequisites

You should be familiar with XAML, Visual C#, and events.

The device or emulator that you're using must support an ambient light sensor.

Time to complete: 20 minutes.

Instructions

1. Open Microsoft Visual Studio

Open an instance of Microsoft Visual Studio.

2. Create a new project

Create a new project, choosing a Blank App from the Visual C#/Store Apps project types.

3. Replace the C# code

Open your project's BlankPage.xaml.cs file and replace the existing code with the following.


using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

using Windows.UI.Core; // Required to access the core dispatcher object
using Windows.Devices.Sensors; // Required to access the sensor platform and the ALS

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/p/?linkid=234238

namespace App1
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class BlankPage : Page
    {
        private LightSensor _lightsensor; // Our app's lightsensor object
       
        // This event handler writes the current light-sensor reading to 
        // the textbox named "txtLUX" on the app's main page.

        private void ReadingChanged(object sender, LightSensorReadingChangedEventArgs e)
        {
            Dispatcher.RunAsync(CoreDispatcherPriority.Normal, (s, a) =>
            {
                LightSensorReading reading = (a.Context as LightSensorReadingChangedEventArgs).Reading;
                txtLuxValue.Text = String.Format("{0,5:0.00}", reading.IlluminanceInLux);
            });
        }

        public BlankPage()
        {
            InitializeComponent();
            _lightsensor = LightSensor.GetDefault(); // Get the default light sensor object

            // Assign an event handler for the ALS reading-changed event
            if (_lightsensor != null)
            {
                // Establish the report interval for all scenarios
                uint minReportInterval = _lightsensor.MinimumReportInterval;
                uint reportInterval = minReportInterval > 16 ? minReportInterval : 16;
                _lightsensor.ReportInterval = reportInterval;

                // Establish the even thandler
                _lightsensor.ReadingChanged += new TypedEventHandler<LightSensor, LightSensorReadingChangedEventArgs>(ReadingChanged);
            }

        }

    }
}


You'll need to rename the namespace in the previous snippet with the name you gave your project. For example, if you created a project named LightingCS, you'd replace namespace App1 with namespace LightingCS.

4. Replace the XAML code

Open the file MainPage.xaml and replace the original contents with the following XML.


<Page
    x:Class="App1.BlankPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App1"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid x:Name="LayoutRoot" Background="Black">
        <TextBlock HorizontalAlignment="Left" Height="44" Margin="52,38,0,0" TextWrapping="Wrap" Text="LUX Reading" VerticalAlignment="Top" Width="150"/>
        <TextBlock x:Name="txtLuxValue" HorizontalAlignment="Left" Height="44" Margin="224,38,0,0" TextWrapping="Wrap" Text="TextBlock" VerticalAlignment="Top" Width="217"/>


    </Grid>

</Page>

You'll need to replace the first part of the class name in the previous snippet with the namespace of your app. For example, if you created a project named LightingCS, you'd replace x:Class="App1.MainPage" with x:Class="LightingCS.MainPage". You should also replace xmlns:local="using:App1" with xmlns:local="using:LightingCS".

5. Build, deploy and run the app

Press F5 or select Debug > Start Debugging to build, deploy, and run the app.

Once the app is running, you can change the accelerometer values by moving the device or using the emulator tools.

6. Stop the app

  1. Press ALT+Tab to return to Visual Studio.
  2. Press Shift+F5 or select Debug > Stop Debugging to stop the app.

Summary

The previous example demonstrates how little code you'll need to write in order to integrate light-sensor input in your app.

The app establishes a connection with the default sensor in the BlankPage method.


_lightsensor = LightSensor.GetDefault(); // Get the default light sensor object
  

The app establishes the report interval within the BlankPage method. This code retrieves the minimum interval supported by the device and compares it to a requested interval of 16 milliseconds (which approximates a 60-Hz refresh rate). If the minimum supported interval is greater than the requested interval, the code sets the value to the minimum. Otherwise, it sets the value to the requested interval.


uint minReportInterval = _accelerometer.MinimumReportInterval;
uint reportInterval = minReportInterval > 16 ? minReportInterval : 16;
_accelerometer.ReportInterval = reportInterval;

The new light-sensor data is captured in the ReadingChanged method. Each time the sensor driver receives new data from the sensor, it passes the value to your app using this event handler. The app registers this event handler on the following line.


_lightsensor.ReadingChanged += new TypedEventHandler<LightSensor, 
LightSensorReadingChangedEventArgs>(ReadingChanged);

These new values are written to a TextBlock found in the project's XAML.


<TextBlock HorizontalAlignment="Left" Height="44" Margin="52,38,0,0" TextWrapping="Wrap" Text="LUX Reading" VerticalAlignment="Top" Width="150"/>
 <TextBlock x:Name="txtLuxValue" HorizontalAlignment="Left" Height="44" Margin="224,38,0,0" TextWrapping="Wrap" Text="TextBlock" VerticalAlignment="Top" Width="217"/>


Related topics

LightSensor class
LightSensor Sample
Roadmap for creating Windows Store apps using C#, C++, or Visual Basic

 

 

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