从MainActivity调用新活动的方法

Question

There are two Activities..
1. Open SecondActivity from MainActivity
2. When event comes into MainActivity, call testMethod of SecondActivity

But how to do call this testMethod?

public class MainActivity extends Activity implements someListener {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Launch SecondActivity here!!
        Intent intent = new Intent();
        intent.setClass(MainActivity.this, SecondActivity.class);
        startActivityForResult(intent, ID_PlayerActivity);
    }

    //trigger by JNI, it's in the other thread, not main thread.
    void onEventCome() {
        //How to call testMethod() in SecondActivity?
    }
}

---

public class SecondActivity extends Activity {
    void testMethod() {
        //execute something...
    }
}

Answer 1

First you need an event aware listener that will capture such an event happening. Your class seems ill equipped to do so.

Since you have a valid question, here goes:

void onEventCome() {
    SecondActivity secondActivity = new SecondActivity();
    secondActivity.testMethod();
}

Answer 2

There are many ways. For eg: Create the method as static and use class name and call it.

public static void onEventCome() {

}

In MainActivity:

MainActivity.onEventCome();

This is one method. Another method is create an object for MainActivity.

public void onEventCome() {

}

MainActivity main;

main = new MainActivity();
main.onEventCome();

Answer 3

If you open the SecondActivity, your MainActivity becomes inactive. I don't believe it is a good idea to call some activity method from other inactive/stopped activity.

I suggest to use observer pattern . Create a global long-lived object like EventProducer and register all activities as observer. So your EventProducer can inform all Activities about new event.

Example:

public class SecondActivity extends Activity implements MyEventListener {

    @Override
    public void onResume(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventProducer.instance().register(this);
    }

    @Override
    public void onPause(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventProducer.instance().unregister(this);
    }

    void testMethod(){
        //just doit
    }

    @Override
    void onMyEventCome() {
        testMethod();
    }
}

Answer 4

You don't have a content view for your second activity. If you don't need to see the operation happen, you could remove your

Intent intent = new Intent();
    intent.setClass(MainActivity.this, SecondActivity.class);
    startActivityForResult(intent, ID_PlayerActivity);

remove extends Activity in SecondActivity and add a constructor public SecondActivity(Context context) and invoke the test method from your first activity like @Dragan example:

void onEventCome() {
    SecondActivity secondActivity = new SecondActivity(MainActivity.this);
    secondActivity.testMethod();
}