Android: Fragment cannot get activity

问题:

I have an activity which does a fragment transaction

DetailFragment newFragment = new DetailFragment();
transaction.replace(R.id.mylist, newFragment);
transaction.addToBackStack(null);
transaction.commit();

that works fine. Now I know within my activity a dynamic string I need to replace in the layout I have in newFragment. I thought that I can call after transaction.commit() just something like

newFragment.setMyString("my dynamic value");

And in the newFragment.java I have

public void setMyString(String s)
{
 TextView tv = (TextView) getActivity().findViewById(R.id.myobject);
 tv.setText(s);
}

The point is that getActivity() returns null. How can I get the context I need to find my layout elements?

Edit:

I try to follow the route using a bundle as this seems to be the cleanest way. So I have changed my code:

Bundle b = new Bundle();
b.putString("text", "my dynamic Text");
DetailFragment newFragment = new DetailFragment();
transaction.replace(R.id.mylist, newFragment);
transaction.addToBackStack(null);
transaction.commit();

My fragment onCreateView looks like this:

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 
{
   View v = inflater.inflate(R.layout.mylayout, container, false);
   TextView t = (TextView) v.findViewById(R.id.texttobereplaced);
   t.setText(savedInstanceState.getString("text");
}

It seems that savedInstranceState is empty. Where should I find my bundle?

Edit2:

missed the getArguments() in the reply. is working now.

回答1:

Your Fragment hasn't attached to the Activity yet, which also means your layout hasn't been inflated yet (See the Fragment lifecycle). The best solution here would be to add your String value as an argument to the Fragment via the Fragment.setArguments(Bundle) method. This can be retrieved in the receiving Fragment via the Fragment.getArguments() method.

回答2:

Make sure you call getActivity() in or after onAttach(), as before then it will return null.

回答3:

So i am also using the same fragment transaction manager and the only problem i can see with your code is that you define the TextView tv inside your onCreateView method of your newFragment class and then instantiate it as like this :

public class AboutFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.newFragment, container, false);
        TextView tv = (TextView) v.findViewById(R.id.textview);
        return v;
    }

    public void setMyString(String s) {
        tv.setText(s);
    }
}

I know it does'nt make really much sense but that is how i am running my code and it works fine :)

回答4:

if u need to call getActivity in OnCreateView, move all ur code from onCreateView to onActivityCreate and only left lines

View v = inflater.inflate(R.layout.xxxx, container, false);
    return v;

in onCreateView

but i have a funny situation.

in My onActivityCreated

Spinner s1 = (Spinner) getActivity().findViewById(R.id.bitlength);
    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
            getActivity(), R.array.bitlengths,
            android.R.layout.simple_spinner_item);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    s1.setAdapter(adapter);

Sometime the onActivityCreated wont run (correctly!?) and hence the spinner s1 become empty.