Call a public method in the Activity class from another class?

Question

MAIN ACTIVITY

    public class MyActivity() extends Activity
    {
        onCreate()
        {
            MyClass myobj=new MyClass();    
        }
               


        

Answer 1

I had an inner class that I wanted to pull out into a more general library "Helper" class. I had the same issue you do. I got around it by making the helper class abstract, with a single abstract method. Then in my project package I extended the helper class with a constructor call in the specific class.

public class MyActivity extends Activity {
    onCreate() {
        MyHelperClass = new MyHelperClass(this, "foobar");
    }

    public void myMethod() {
        // Code...
    }
}

// In a different file
public class MyHelperClass extends HelperClass {
    private MyActivity mInstance;

    public MyHelperClass(MyActivity act, String data) {
        super();
        this.mInstance = act;
        this.mActivity = act;  // Useful for calling generic Activity methods in the HelperClass
        this.mData = data;
    }

    protected void callMyActivityMethod() {
        mInstance.myMethod();
    }
}

// In a different file
public abstract class HelperClass {
    protected Activity  mActivity;
    protected String    mData;

    public HelperClass() {
        // Subclass will set variables
    }

    protected abstract void callMyActivityMethod();

    // More code for all the other stuff the class does
}

In this way, I have a helper class that contains the vast majority of the "work", and all I have to do is make a subclass with the constructor and one method in order to get access to the calling activity's method of interest.

Answer 2

This is probably the best way to do it. This is how I'm doing it. It's called a Singleton Design Pattern:

public class MyActivity extends Activity {
    private static MainActivity instance;

    public static MainActivity getInstance() {
     if(instance==null){
          setInstance(this);
        }
        return instance;
    }

    public static void setInstance(MainActivity instance) {
        MainActivity.instance = instance;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setInstance(this);
    }
}