Reflection for a Field going wrong

Question

Hi, I have been trying to use reflection for a specifiec Field in the android.os.build class, the MANUFACTURER field... I have tried by using this code :

try
    {
        Class myBuildClass = android.os.Build.class;
        Field m1 = Build.class.getDeclaredField("MANUFACTURER");
        validField = true;

        manufacturer = Build.MANUFACTURER;
    }
    catch(Exception ex)
    {
        manufacturer = Build.PRODUCT;
        System.err.println("getDeviceSpecifics, got an exception during getting Field : " + ex.toString());
    }

I am gettign the following errors :

06-01 11:26:37.639: WARN/dalvikvm(7342): VFY: unable to resolve static field 2 (MANUFACTURER) in Landroid/os/Build;
06-01 11:26:37.639: WARN/dalvikvm(7342): VFY:  rejecting opcode 0x62 at 0x0048

06-01 11:26:37.639: WARN/dalvikvm(7342): VFY:  rejected Lmypackage/android/managementModule/Management;.getDeviceSpecifics ()V
06-01 11:26:37.639: WARN/dalvikvm(7342): Verifier rejected class Lmypackage/android/managementModule/Management;

And when debugging I noticed that InvocationtargetException is continuesly thrown, so I am guessing I haven't been implementing the whole Reflection principle correctly... Any idea where things are going wrong or otherwise on how to implement Refelction for a single Field correctly ?

Answer 1

This field is public. You dont need reflection to read it.

But there are several problems in your code which cause this error:

Class myBuildClass = android.os.Build.class;
Field m1 = Build.class.getDeclaredField("MANUFACTURER");

You defining myBuildClass but later you're never using it. The same for field m1. And after that your just directly accessing it by calling

Build.MANUFACTURER;

Then what is the whole refleciton stuff used?

If it would be private you do it the following way:

Field manufacturer = android.os.Build.class.getDeclaredField("MANUFACTURER");
manufacturer.setAccessible(true);
int myManufacturer = manufacturer.getInt(android.os.Build.class);

Note: manufacturer.getInt(android.os.Build.class) is only possible because its a static field. Otherwise you would need to pass an actual object of this class.

I saw in your comments that you want to check if the field is available. The field will always be available, but maybe it has different values from time to time. Why shouldn't it be available?

Ok now i also saw in your comments that you want to do it for 1.6. Take a look at the documentation and you will see hat this field was added at API level 1.4.

Your code may work in 1.6, but i'll have to mention that i think its really unnecessary and partly also wrong.

Answer 2

If you look at the API docs, you'll see that Build.Manufacturer is available since API level 4 only. That means that if you run your code on an Android device of API version 3 or lower, it will fail since that field does not exist.

Answer 3

From reading the comments to the other questions, I now understand better why you can not just directly access the field. Because your code may run an a pre version 4.0 Android.

Still, I do not think reflection is necessary. How about

try
{
     Build . MANUFACTURER ;
     // do stuff with Build . MANUFACTURER 
}
catch ( AppropriateException )
{
     // pre version 4.0 Contingency Plan
}

Answer 4

Wouldn't it be easier to check the SDK version first rather then looking for the field via reflection?

if (Build.VERSION.SDK_INT >= 4) {
    return Build.MANUFACTURER;
} else {
    return Build.PRODUCT;
}

Answer 5

@Sebi, hereby the whole code, I have placed it as an "answer" because posting code in those comments is pretty unreadable

String manufacturer;
try //reflection
        {
            Field manufacturerField = android.os.Build.class.getDeclaredField("MANUFACTURER");
            manufacturerField.setAccessible(true);
            int myManufacturer = manufacturerField.getInt(android.os.Build.class);
            manufacturer = Build.MANUFACTURER;
        }
        catch(Exception ex)
        {
            manufacturer = Build.PRODUCT;

        System.err.println("getDeviceSpecifics, got an exception during getting Field : " + ex.toString());
    }

This WON'T work on my 1.5 device. That's because the line

manufacturer = Build.MANUFACTURER;

is there, so if that one is ommitted as in :

 try    //reflection
    {
        Field manufacturerField = android.os.Build.class.getDeclaredField("MANUFACTURER");
        manufacturerField.setAccessible(true);
        int myManufacturer = manufacturerField.getInt(android.os.Build.class);
    }
    catch(Exception ex)
    {
        manufacturer = Build.PRODUCT;

        System.err.println("getDeviceSpecifics, got an exception during getting Field : " + ex.toString());
    }

It actually will work, the problem obviously is that I also want that single line in my code, so that on a 1.6 Device I can retrieve manufacturer = Build.MANUFACTURER;

btw, I just tested all suggestions on a 1.5 device AND 1.5 emulator and they both throw errors, the funny part is that even the shortest code within a try-catch construction will still throw an

06-02 09:26:54.741: ERROR/AndroidRuntime(782): Uncaught handler: thread main exiting due to uncaught exception
06-02 09:26:54.791: ERROR/AndroidRuntime(782): java.lang.VerifyError: mypackage.android.Reflection.reflectiontest

Answer 6

I've had a simular issue, here is the relevant snippet I played with:

try {
    return android.os.Build.class.getField("MANUFACTURER").get(null).toString();
} catch (Exception e) {
    return "???";
}

Answer 7

Perfect solution

try // reflection
  {
   Field manufacturerField = android.os.Build.class
     .getDeclaredField("MANUFACTURER");
   manufacturerField.setAccessible(true);
   String manufacturerName = manufacturerField.get(
     android.os.Build.class).toString();
   System.out.println("manufacturerName: " + manufacturerName);

  } catch (Exception ex) {

   System.err
     .println("getManufacturerName, got an exception during getting Field : "
       + ex.toString());
  }