Question

I have a class SomeTaskManager with an abstract method runATask.
I want to execute the runATask method via reflection,
this is my code : what am I missing?

SomeTaskManager pm= (SomeTaskManager)context.getSomeTaskManager(); 
Class c = Class.forName( pm.getClass().getName() ); 

Method[] allMethods = c.getDeclaredMethods();

for (Method m : allMethods) {
    if (!m.getName().equals("runATask")) {
        continue;
    }
    m.invoke( c ,new Object[] { someParam, null, 1});
    break;
}  

I’m getting this errors

java.lang.IllegalArgumentException: object is not an instance of the class
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at de.vogella.android.downloadmanager.DownloadManagerActivity.riflesso(DownloadManagerActivity.java:250)
at de.vogella.android.downloadmanager.DownloadManagerActivity.onCreate(DownloadManagerActivity.java:68)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
at android.app.ActivityThread.access$1500(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3835)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)

Answer 1

java.lang.IllegalArgumentException: object is not an instance of the class
    at java.lang.reflect.Method.invoke(Method.java:507)

Aha, here

m.invoke(c, new Object[] { someParam, null, 1});

you’re passing the Class instead of an instance of it. You need to pass pm (the concrete instance) to it instead:

m.invoke(pm, new Object[] { someParam, null, 1});

This problem would likely be spotted sooner by just reading the code if you used full and self-documenting variable names instead of nothing-saying abbreviations. I’d suggest to work on that as well.

---

Unrelated to the concrete problem, the following line

Class c = Class.forName( pm.getClass().getName() ); 

can be simplified as follows

Class c = pm.getClass();