修复 XE8 for Android 方向传感器 headingX,Y,Z 不会动的问题

问题：XE8 for Android 方向传感器无法正常运作（在 XE7 是正常的）

测试：官方示例 Samples\Object Pascal\Mobile Snippets\OrientationSensor\

适用：XE8 for Android

修复方法：

请将源码 System.Android.Sensors.pas 复制到自己的工程目录里，再进行修改。

修改下面代码：

  TAndroidNativeMagneticSensor = class(TCustomOrientationSensor)

  strict private

    FNativeSensor: TNativeSensor;

  protected

    function GetUpdateInterval: Double;  override;

    procedure SetUpdateInterval(AInterval: Double); override;

    function GetOrientationSensorType: TOrientationSensorType; override;

{+++>} // 加入下面二行代码

    function DoStart: Boolean; override;

    procedure DoStop; override;

{<+++}

    function GetSensorCategory: TSensorCategory; override;

    function GetState: TSensorState; override;

    function GetTimeStamp: TDateTime; override;

    function GetAvailableProperties: TCustomOrientationSensor.TProperties; override;

    function GetDoubleProperty(Prop: TCustomOrientationSensor.TProperty): Double; override;

  public

    constructor Create(AManager: TSensorManager); override;

    function Supported: Boolean;

  end;

找到 TAndroidNativeMagneticSensor.Create 加入下面代码：

... 略 ...

constructor TAndroidNativeMagneticSensor.Create(AManager: TSensorManager);

begin

  inherited;

  FNativeSensor := TNativeSensor.Create(ASENSOR_TYPE_MAGNETIC_FIELD);

end;

{+++>} // 加入下面代码

function TAndroidNativeMagneticSensor.DoStart: Boolean;

begin

  Result := FNativeSensor.DoStart;

end;

procedure TAndroidNativeMagneticSensor.DoStop;

begin

  inherited;

  FNativeSensor.DoStop;

end;

{<+++} // 加入上面代码 

... 略 ...