Windows phone罗盘传感器

电子罗盘，也叫数字指南针，是利用地磁场来定北极的一种方法。WP手机设备里面我们可以利用罗盘传感器的API来实现电子罗盘的功能。

(1)调用

罗盘传感器的类：Compass

该类位于Microsoft.Devices.Sensors的命名空间，在开始的时候，需要使用using引入；

(2)Compass的属性，事件，方法

（3）实现电子罗盘：

xaml文件：

<Page
    x:Class="Toly.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Toly"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <StackPanel >
        <TextBlock Text="磁场北："/>
        <TextBlock x:Name="magneticNorth" Foreground="#FFC8C7CC"/>
        <TextBlock Text="地理北："/>
        <TextBlock x:Name="trueNorth" Foreground="#FFC8C7CC"/>
        <TextBlock Text="精度"/>
        <TextBlock x:Name="headingAccuracy" Foreground="#FFC8C7CC"/>
        <Grid>
            <Ellipse Height="375" Width="375" 
                     HorizontalAlignment="Center" 
                     VerticalAlignment="Center" 
                     x:Name="EllipseBorder"
                     Stroke="#FFF80D0D" StrokeThickness="2"
                     Fill="White"/>
            <Image Height="263" Width="263" HorizontalAlignment="Center"
                   VerticalAlignment="Center" x:Name="CompassFace" 
                   Source="Assets/compass.png" Stretch="None"/>
            <Ellipse Height="263" Width="263" x:Name="EllipseGlass"
                     Stroke="Black" StrokeThickness="1">
                <Ellipse.Fill>
                    <LinearGradientBrush EndPoint="1,0.5" StartPoint="0,0.5">
                        <GradientStop Color="#A5000000" Offset="0"/>
                        <GradientStop Color="#BFFFFFFF" Offset="1"/>
                    </LinearGradientBrush>
                </Ellipse.Fill>
            </Ellipse>
         </Grid>
        <Grid>
            <Image Height="200" Width="200" HorizontalAlignment="Center"
                   VerticalAlignment="Center"
                   Source="Assets/calibrate_compass3.png"
                   x:Name="CompassSuggest" />
        </Grid>
    </StackPanel>
</Page>

实现的效果图如下：

这个上述的xaml不过多介绍，接下来，我们重点看的是C#的代码

//mainpage加载完成，实例化罗盘对象
private async void MainPage_Loaded(object sender , RoutedEventArgs e) {
    compass = Compass.GetDefault();//得到罗盘对象
    if (compass == null) {
     await new Windows.UI.Popups.MessageDialog("不支持罗盘传感器").ShowAsync();
     return;
    }
    compass.ReadingChanged += compass_ReadingChanged;//开始监听事件
}

private async void compass_ReadingChanged(object sender, CompassReadingChangedEventArgs args)
{
      //Lambda 表达式
    await this.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
    {
      //args是罗盘对象数据的类的基类,用于传递事件的细节。
      CompassReading reading = args.Reading;
      magneticNorth.Text = string.Format("{0,5:0.00}",reading.HeadingMagneticNorth);
      if(reading.HeadingTrueNorth != null)
      {
           trueNorth.Text = string.Format("{0,5:0.00}", reading.HeadingTrueNorth);
       }
      else
      {
          trueNorth.Text = "没有数据";
      }
      switch(reading.HeadingAccuracy){
      //准确性不可用
          case MagnetometerAccuracy.Unknown:
                         headingAccuracy.Text = "请按照下方图片移动方向移动手机";
                         if (CompassSuggest.Visibility != Visibility.Visible)
                         {
                             CompassSuggest.Visibility = Visibility.Visible;
                         }
                         break;
         //高精度，不需要校准
         case MagnetometerAccuracy.High:
                        headingAccuracy.Text = "高精度";
                        if (CompassSuggest.Visibility == Visibility.Visible)
                        {
                            CompassSuggest.Visibility = Visibility.Collapsed;
                        }
                        break;
         //实际值和报告值高度不准确,需要用户校准
         case MagnetometerAccuracy.Unreliable:
                        headingAccuracy.Text = "请按照下方图片移动方向移动手机";
                        if (CompassSuggest.Visibility != Visibility.Visible)
                        {
                            CompassSuggest.Visibility = Visibility.Visible;
                        }
                        break;
         //实际值和报告值不同，但其准确性已足以满足某些应用领域
         case MagnetometerAccuracy.Approximate:
                        headingAccuracy.Text = "一般精度";
                        if (CompassSuggest.Visibility == Visibility.Visible)
                        {
                            CompassSuggest.Visibility = Visibility.Collapsed;
                        }
                        break;
         default:
                        if (CompassSuggest.Visibility != Visibility.Visible)
                        {
                            CompassSuggest.Visibility = Visibility.Visible;
                        }
                        headingAccuracy.Text = "请按照下方图片移动方向移动手机";
                        break;
          }
          double TrueHeading = reading.HeadingTrueNorth.Value;
          //电子磁盘的角度调整     
          CompassFace.RenderTransformOrigin = new Point(0.5,0.5);
          EllipseGlass.RenderTransformOrigin = new Point(0.5,0.5);
          RotateTransform transform = new RotateTransform();
          transform.Angle = 360 - TrueHeading;//偏移的角度
          CompassFace.RenderTransform = transform;
          EllipseGlass.RenderTransform = transform;
   });
}