如何在Android studio java的textview中显示另一个类的变量？

Question

So I have a GPS tracking app and I want to show my data (distance, speed etc) in one of the UI.

My LocationService.java tracks all the metrics in a foreground service:

public class LocationService extends Service implements LocationListener{

public ArrayList<Location> lastLocationResultArray = new ArrayList<>();
public float distance;
public float distanceKm;
public float ascent;
public float descent;
public float currentSpeed;
Location changedLocation;
double currentAltitude;
public float averageSpeed;

private static DecimalFormat df1 = new DecimalFormat("#");
private static DecimalFormat df2 = new DecimalFormat("#.#");
private static DecimalFormat df3 = new DecimalFormat("#.##");

public static final String EXTRA_DISTANCE = "com.example.iathleticsrecorder.EXTRA_DISTANCE";

public LocationCallback locationCallback = new LocationCallback(){
    @Override
    public void onLocationResult(LocationResult locationResult) {
        super.onLocationResult(locationResult);
        if(locationResult != null && locationResult.getLastLocation() != null){
            Location actualLocation = locationResult.getLastLocation();
            double latitude = locationResult.getLastLocation().getLatitude();
            double longitude = locationResult.getLastLocation().getLongitude();
            double altitude = locationResult.getLastLocation().getAltitude();
            double speed = locationResult.getLastLocation().getSpeed();
            Log.d("LOCATION_UPDATE", latitude + ", " + longitude + ", " + altitude + ", " + locationResult);

            currentSpeed = (float) (speed*3.6f);
            
            changedLocation = actualLocation;

            if(!lastLocationResultArray.isEmpty()) {
               distance += changedLocation.distanceTo(lastLocationResultArray.get(lastLocationResultArray.size() - 1));
                distanceKm = distance/1000;

                Location lastlocation = lastLocationResultArray.get(lastLocationResultArray.size() - 1);
                double lastAltitude = lastlocation.getAltitude();
                double altitudeChange = altitude-lastAltitude;
                if(altitudeChange<-9) {
                    descent += altitudeChange;
                } else if(altitudeChange>9) {
                    ascent += altitudeChange;
                }

            }

            lastLocationResultArray.add(changedLocation);
            Log.d("ENDOFLOOP", distanceKm + ", " + distance + ", " + ascent + ", " + descent + ", " + currentSpeed + " ," + averageSpeed );
        }
    }
};

public String getDistance() {
    return df3.format(distance);
}

Here is an example of how all the metrics are added up from the "Log.d (ENDOFLOOP)":

2020-10-05 19:32:55.486 20116-20116/com.example.iathleticsrecorder D/ENDOFLOOP: 0.0042962608858942986, 4.296261, 4.296261, 22.800003, -22.800003, 0.08298418 ,0.0

So I know that the variables declared at the top of the LocationService-class is changing (as seen in the log.d), but when I try to get the data from the other class, it will only show "0" in the textview's, as if it does not take the updated value from LocationService.class, but only the declared value (even though I have not decared any value, only the variable). Here's a snippet of the code that is connected to the UI in the StartedSession.java:

I declare the LocationService-class:

LocationService mLocationService = new LocationService();

And use a getter to get the value of the float variable via a button:

        btUpdateNumbers = findViewById(R.id.btUpdateNumbers);
    btUpdateNumbers.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            txtViewDistance.setText(mLocationService.getDistance());
            //txtViewCurrentSpeed.setText(mLocationService.getSpeed());
        }
    });

Why is it only showing "0"?

Answer 1

使用 SharedPreferences 可以帮助您解决问题。