Question

I have application using Android 2.1 which utilize LocationManager to get the altitude. But now, I need to obtain the altitude using SensorManager which requires API Level 9 (2.3).

How can I put the SensorManager.getAltitude(float, float) in my 2.1 android application by putting a condition and calling it by a function name (possible in normal Java)?

Thank you in advance

UPDATE 1
If you have noticed that my application need to be compiled using Android 2.1. That’s why I’m looking for a way to call the function by name or in any other way that can be compiled.

Answer 1

You can call the method using reflection and fail gracefully in case of errors (like missing class or methods). See java.lang.reflect

Other option is to compile code in level 9 but surround with try/catch to catch errors that would arise from execution on lower level. It could be fairly error prone, though, and I’d think twice about doing it.

---

Update

Here is test code

public void onCreate(Bundle savedInstanceState)
{
    try {
        // First we try reflection approach.
        // Expected result
        //    in 2.3 we print some value in log but no exception
        //    in 2.2 we print NoSuchMethodException
        // In both levels we get our screen displayed after catch
        Method m = SensorManager.class.getMethod("getAltitude",Float.TYPE, Float.TYPE);
        Float a = (Float)m.invoke(null, 0.0f, 0.0f);
        Log.w("test","Result 1: " + a);
    } catch (Throwable e) {
        Log.e("test", "error 1",e);
    }

    try {
        // Now we try compiling against 2.3
        // Expected result
        //    in 2.3 we print some value in log but no exception
        //    in 2.2 we print NoSuchMethodError (Note that it is an error not exception but it's still caught)
        // In both levels we get our screen displayed after catch
        float b = SensorManager.getAltitude(0.0f, 0.0f);
        Log.w("test","Result 2: " + b);

    } catch (Throwable e) {
        Log.e("test", "error 2",e);
    }

    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

Results:

2.3

09-14 07:04:50.374: DEBUG/dalvikvm(589): Debugger has detached; object registry had 1 entries
09-14 07:04:50.924: WARN/test(597): Result 1: NaN
09-14 07:04:51.014: WARN/test(597): Result 2: NaN
09-14 07:04:51.384: INFO/ActivityManager(75): Displayed com.example/.MyActivity: +1s65ms

2.2

09-14 07:05:48.220: INFO/dalvikvm(382): Could not find method android.hardware.SensorManager.getAltitude, referenced from method com.example.MyActivity.onCreate
09-14 07:05:48.220: WARN/dalvikvm(382): VFY: unable to resolve static method 2: Landroid/hardware/SensorManager;.getAltitude (FF)F
09-14 07:05:48.220: DEBUG/dalvikvm(382): VFY: replacing opcode 0x71 at 0x0049
09-14 07:05:48.220: DEBUG/dalvikvm(382): VFY: dead code 0x004c-0064 in Lcom/example/MyActivity;.onCreate (Landroid/os/Bundle;)V
09-14 07:05:48.300: ERROR/test(382): error 1
        java.lang.NoSuchMethodException: getAltitude
        at java.lang.ClassCache.findMethodByName(ClassCache.java:308)

Skipped stack trace

09-14 07:05:48.300: ERROR/test(382): error 2
    java.lang.NoSuchMethodError: android.hardware.SensorManager.getAltitude
    at com.example.MyActivity.onCreate(MyActivity.java:35)

Skipped more stack trace

09-14 07:05:48.330: DEBUG/dalvikvm(33): GC_EXPLICIT freed 2 objects / 64 bytes in 180ms
09-14 07:05:48.520: INFO/ActivityManager(59): Displayed activity com.example/.MyActivity: 740 ms (total 740 ms)