Android，Access Fragment方法来自单独的类

Question

I have a Fragment :

public class CustomFrag extends Fragment{
    ...
    public void refreshList(){
        ...
    }
}

I have a separate Class :

public class SomeClass{
    ...
}

I am trying to call refreshList() from SomeClass :

String tagName = "android:switcher:" + R.id.pager + ":" + 1;
CustomFrag f2 = (CustomFrag)getActivity().getSupportFragmentManager().findFragmentByTag(tagName);
f2.refreshList();

But this shows Cannot resolve method 'getActivity' . If I add to the class:

extends Fragment

All the warnings go away, but the app crashes, with a null-pointer exception to the CustomFrag f2 = (CustomFrag)... line.

I have another fragment, contained within the same parent as CustomFrag , and the method call described above works great.

How can I access the CustomFrag methods from SomeClass ? This question (and similar) are asked all over, but most do not have accepted answers, or else have very vague ones that are of little help.

Thanks in advance.

Edit: Temp solution

I am calling methods that belong to SomeClass from within the two aforementioned Fragments. What I came up with is the following:

Within FragOne

public class FragOne extends Fragment{

    ...

    String tagName = "android:switcher:" + R.id.pager + ":" + 1;
    CustomFrag f2 = (CustomFrag)getActivity().getSupportFragmentManager().findFragmentByTag(tagName);
}

And then:

public class FragOne extends Fragment{

    ...

    String tagName = "android:switcher:" + R.id.pager + ":" + 1;
    CustomFrag f2 = (CustomFrag)getActivity().getSupportFragmentManager().findFragmentByTag(tagName);

    SomeClass obj = new SomeClass(...);
    obj.someMethod(f2);
}

Where someMethod then can use

f2.refreshList();

This solves the issue I have been having, but it would still be nice to know a more direct way to access the Fragment's methods via a separate Class.

Further answers that solve this problem are welcome, and will be accepted as solution.

Answer 1

HomeFragment.java

public class HomeFragment extends Fragment {

    private static HomeFragment instance;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_home, container, false);

        instance = this;

        return view;
    }

    public static HomeFragment getInstance() {
        return instance;
    }

    public void myMethod() {
        // do something...
    }

}

AnotherClass.java

public Class AnotherClass() {
     // call this method
     HomeFragment.getInstance().myMethod();
}

Answer 2

The issue is that you need to get the activity context of the fragments. You cannot just make up a new class extending a fragment class, without actually instantiating the fragment and associating it with an activity, and hope to get back your activity context from it.

If you wish to use SomeClass independent of the Fragment, you can declare a variable to hold the parent activity

private FragmentActivity mActivity;

and then in the constructor, you may pass the activity context reference into it.

public SomeClass (FragmentActivity activity) {
    mActivity = activity;
    ...
}

Afterwards, you can call

mActivity.getSupportFragmentManager().findFragmentByTag(tagName);

when you need it within SomeClass .

Answer 3

Create interface for that

public interface Callback{
void refreshList();
}

This is your fragment

public class CustomFrag extends Fragment implements Callback{
...

new SomeClass().setListener(CustomFrag .this);

@Override
  public void refreshList(){

//do work
 }
}

Write your class

 public class SomeClass{
 private Callback mCallback;

 public void setListener(Callback callBack){
 mCallback=callBack;
  }
}

call Fragment refreshListview from your SomeClass like this

mCallback.refreshListView();