Android Accelerometer issues

Question

I am working on a game that involves using the accelerometer to control the character. My problem is this: I need to use the values recieved by the sensor in classes and methods that are not accessible inside OnSensorChanged(). I believe I need to implement a Callback from inside the OnSensorChanged, but I don't know how to do that. Can anyone help me out?

Well, I'm just registering the SensorListener to my accelerometer class, and I have OnSensorChanged inside of that class. That's pretty much all of my code, because nothing else worked. I get my accelerometer values just fine, but I can't seem to take them and save them to a variable. That's what I really want to do, but the variables always only exist inside of OnSensorChanged. If I can just save the values, I would have no more problems. — vulgarknight, Mar 10 '13 at 20:48
Why can't you define a class member to hold the values passed by onSensorChanged. — Hoan Nguyen, Mar 10 '13 at 21:16

score 0 · Accepted Answer · edited May 23 '17 at 12:21

I believe the answer in this post (How to Define Callbacks in Android?) will help you out.

To summarize, create the callback interface:

// The callback interface
interface MyCallback {
    void callbackCall(SensorEvent event);
}

Implement the call back interface in the class that is supposed to do calculations:

class Callback implements MyCallback {
    void callbackCall(SensorEvent event) {
       // callback code goes here
    }
}

Make the call from your Activity where you have the onSensoreChanged():

// The class that takes the callback
class Worker extends Activity implements SensorEventListener {
    MyCallback callback;

    public void onSensorChanged(SensorEvent event) {

      callback.callbackCall(event);
   }
}

I hope this helps.

UPDATE:

I assume you already know about processes and threads (if not, please have a look at the Android doc about Processes and Threads).

The onSensorChanged method is an I/O and it is a good practice to do I/O operations in a separate thread (instead of the main UI thread).

Once the callback method is called, you can store the event in another variable and use those local variables in that class.

Since you are writing a game, it is unlikely for your app to require every single event. Therefore, while the app is busy calculating data for your game, the other events can be dropped. You can do this by setting a "busy" flag (boolean) and include the code for calculation within this if block.

    void callbackCall(SensorEvent event) {
        if (!busy) {
            // Set the busy flag to block other event changes
            busy = true;
            // callback code goes here

            // Once finished, reset the busy flag to allow other events to come in
            busy = false;
        }
    }

So, if I was to have my characters X and Y coordinates in one class, and my accelerometer sensorlistener in another class, I would call the callback in the OnSensorChanged, but how would the event.values exist in the rest of the class that modifies the coordinates? wouldn't those values get thrown out as soon as another method is called from the class that handles the players position? — vulgarknight, Mar 10 '13 at 21:14
Ok, so the callback works on the same thread of the class calling it? So when the callback assigns a value to a variable, that variable is persistent in that class? — vulgarknight, Mar 10 '13 at 21:47
Correct. But please remember in case you read or modify values from fields within your class, synchronize the access to those fields where it is necessary. — Armin, Mar 10 '13 at 22:08

Android Accelerometer issues

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