Question

My problem is simple. So simple I can’t seem to figure it out. I am passing a qualified class name to a BroadcastReceiver as a String in an Intent.

The goal is to instantiate an object from the class name using reflection, and call a method which we know exists, because it implements a proprietary interface. I am even checking it against getDeclaredMethods() which says its there, but when I try to invoke that method, it throws a java.lang.NoSuchMethodException.

String myClass = intent.getStringExtra("name");        
Class<?> c = Class.forName(myClass);
Object object = c.newInstance();

// Get the files from the interface

Method ms[] = c.getDeclaredMethods();
for (Method m1 : ms) {
    Log.i("METHOD", "METHODS " + m1.getName());
}

Method m = c.getDeclaredMethod("getStrings", (Class<?>) null);
String[] someStrings = (String[]) m.invoke(object, (Object[]) null);

m = c.getDeclaredMethod("getThings", (Class<?>) null);
Thing[] things = (Thing[]) m.invoke(object, (Object[]) null);

Here is the LogCat output:

08-30 23:37:36.150: INFO/METHOD(2336): METHODS getStrings
08-30 23:37:36.150: INFO/METHOD(2336): METHODS getThings
08-30 23:37:36.150: WARN/System.err(2336): java.lang.NoSuchMethodException: getStrings
08-30 23:37:36.150: WARN/System.err(2336):     at java.lang.ClassCache.findMethodByName(ClassCache.java:247)
08-30 23:37:36.150: WARN/System.err(2336):     at java.lang.Class.getDeclaredMethod(Class.java:731)
08-30 23:37:36.150: WARN/System.err(2336):     at com.app.MyBroadcastReceiver.onReceive(MyBroadcastReceiver.java:45)
08-30 23:37:36.150: WARN/System.err(2336):     at android.app.ActivityThread.handleReceiver(ActivityThread.java:1794)
08-30 23:37:36.150: WARN/System.err(2336):     at android.app.ActivityThread.access$2400(ActivityThread.java:117)
08-30 23:37:36.150: WARN/System.err(2336):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:981)
08-30 23:37:36.150: WARN/System.err(2336):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-30 23:37:36.160: WARN/System.err(2336):     at android.os.Looper.loop(Looper.java:130)
08-30 23:37:36.160: WARN/System.err(2336):     at android.app.ActivityThread.main(ActivityThread.java:3683)
08-30 23:37:36.160: WARN/System.err(2336):     at java.lang.reflect.Method.invokeNative(Native Method)
08-30 23:37:36.160: WARN/System.err(2336):     at java.lang.reflect.Method.invoke(Method.java:507)
08-30 23:37:36.160: WARN/System.err(2336):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-30 23:37:36.160: WARN/System.err(2336):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-30 23:37:36.160: WARN/System.err(2336):     at dalvik.system.NativeStart.main(Native Method)

Is there something I am missing here?

Edit: Added the code to the class

public class MyClass implements MyInterface {

    @Override
    public String[] getStrings() {
        // Stub
        return new String[2];
    }

    @Override
    public Thing[] getThings() {
        // Stub
        return new Thing[2];
    }

}

Note: The BroadcastReceiver and the Class are in different projects.

Answer 1

getDeclaredMethod requires you give the right parameters. If there are no parameters, then instead of passing “null”, you need to pass absolutely nothing.

For example, here is a code snippet for hashCode, which takes no arguments

Method m = c.getDeclaredMethod("hashCode");
System.out.println("test");
Method m2 = c.getDeclaredMethod("hashCode", (Class<?>) null);

it will print out “test”, then throw a MethodNotFound exception as hashCode takes no arguments. If you want to get the argument types as well as the name, execute the getParameterTypes on the method object

for (Method m1 : ms) {
    System.out.println( "METHODS " + m1.getName());
    for (Class paramC : m1.getParameterTypes()) {
        System.out.println(paramC.getName());
    }
    }