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

If I'm understanding you correctly I believe you can solve your problems using an interface as a callback.

////ACTIVITY/////////////////////////////////

 public class MyActivity() extends Activity {

    onCreate()
    {
        MyClass myObj=new MyClass();   

        //Set the listener on the object. Created as anonymous
        myObj.setListener(new MyClass.Listener() {
             myMethod();
        });
    }
}

public void myMethod(){

}

//////Custom Class//////////////////

public class MyClass {
     Listener mListener;

     public interface Listener {
          public void onInterestingEvent();
     }

     public void setListener(Listener listener) {
          mListener = listener;
     }

     public void someUsefulThingTheClassDoes() {
          //Do your code here and when you're ready to call the activity's method do this
          mListener.onInterestingEvent();
     }
}

Answer 2

Make that method as static so you can call without creating the class object

public static void Mymethod()
{}

and call like this way

MainActivity.Mymethod();

Answer 3

In MainActivity.class file You have to pass MainActivity context from MainActivity Class. Then in MyClass you have to Get MainActivity context. Remember Context and MyActivity are two different reference.

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

//HELPER CLASS IN A SEPARATE FILE

public class MyClass()
{
    MyActivity context;
    MyClass(MyActivity context)
    {
      this.context = context;

      this.context.Mymethod();
      //Or you can directly use activity context
      context.Mymethod();
    }
}

Answer 4

Why not just pass the activity to the constructor like

public class MyActivity extends Activity { 

   onCreate(){ 
        MyClass myobj=new MyClass(MyActivity.this);     
   } 

   public void myMethod(){

   } 
} 

//HELPER CLASS IN A SEPARATE FILE     
public class MyClass{ 
    public MyClass(MyActivity act) { 
        act.myMethod();
    } 
} 

Answer 5

I decided to write the HelperClass MyClass as an inner class of MyActivity class. This allows it full access to parent class but the bad thing is now MyClass is restricted to MyActivity class only.

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

    } 

    public void myMethod()
    {

    } 
} 
//INNER CLASS
    public class MyClass
    { 
        public MyClass() 
        { 

        } 
        //I can directly access the MyMethod
        myMethod();
    }

Answer 6

You have to pass instance of MainActivity into another class, then you can call everything public (in MainActivity) from everywhere.

MainActivity.java

public class MainActivity extends AppCompatActivity {

    // Instance of AnotherClass for future use
    private AnotherClass anotherClass;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // Create new instance of AnotherClass and
        // pass instance of MainActivity by "this"
        anotherClass = new AnotherClass(this);
    }

    // Method you want to call from another class
    public void myMethod(){
        ...
    }
}

AnotherClass.java

public class AnotherClass {

    // Main class instance
    private MainActivity mainActivity;  

    // Constructor
    public AnotherClass(MainActivity activity) {

        // Save instance of main class for future use
        mainActivity = activity;  

        // Call method in MainActivity
        mainActivity.myMethod();
    }
}