How to read compass orientation?
lazarus / 43-Android

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stab · 2013-05-02 11:37

Hi,

I'm writing a map-app and want to be able to read north direction to
rotate the map as a user changes direction.

Using jni I managed to get hold of the sensorManagerObject but got
stucked when trying to retrieve methodId for defaultSensor needed to
get magnetometer.

Is there some way to get a list of methods and methodId:s via jni?

EDIT:
Documentation for SensorManager is like: public Sensor
getDefaultSensor (int type) and
the sensorManagerClass is retrieved OK through:
  sensorManagerClass := javaEnvRef^^.FindClass(javaEnvRef,
'android/hardware/SensorManager');

To my understanding that would indicate a call like following to
retrieve methodId:
  javaMethodId_getDefaultSensor :=
    javaEnvRef^^.GetMethodID(javaEnvRef, sensorManagerClass,
'getDefaultSensor', '(I)Landroid/hardware/SensorManager;');

Making a call with that code gives: javaMethodId_getDefaultSensor =
nil

Could someone give a clue to whats is wrong?


Regards
stab

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felipemdc · 2013-05-06 06:14

The method parameters descriptor is wrong, it should be:
(I)Landroid/hardware/Sensor;

It returns a Sensor, not a SensorManager

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stab · 2013-05-06 13:21

Thanks for answering Felipemdc,

Noticed that I would be able to achieve what I want through
SensorManager.getOrientation.
Read SensorManager.java and found:
  public static float[] getOrientation(float[] R, float values[])

Modified my code to:
procedure TfrmJNITestMain.GetOrientation;
var
  sensorManagerClass : jclass;
  javaMethodId_getOrientation : JMethodID;
begin
  // get sensorManagerClass
  sensorManagerClass := javaEnvRef^^.FindClass(javaEnvRef,
'android/hardware/SensorManager');
  if sensorManagerClass = nil then
    debugln('******** sensorManagerClass NIL ********')
  else
    debugln('******** sensorManagerClass NOT NIL ********');

  // get MethidId
  javaMethodId_getOrientation :=
  javaEnvRef^^.GetStaticMethodID(javaEnvRef, sensorManagerClass,
'getOrientation', '([F[F)F');
  if javaMethodId_getOrientation = nil then
    debugln('******** javaMethodId_getOrientation NIL ********')
  else
    debugln('******** javaMethodId_getOrientation NOT NIL ********');
end;
   
But still I get method not found.

Could you please tell me what I'm doing wrong?

Regards
stab