设置来自活动的片段的编辑文本，使空指针

Question

I have just started using fragments. I have created a edit text in fragment and I want to fill it from activity but it is giving me null pointer exception. May be OnCreateView runs after fragmenttransaction is committed. I have made it working from another way but I am just a little curious why it is not working. I have searched it but could not find answer of my problem. Any help would be appreciated

Here is my code In activity:

FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Myfragment mFragment = new Myfragment();
fragmentTransaction.replace(R.id.fragment_container, mFragment);
fragmentTransaction.commit();

mFragment.set_fragment_editext("Hello world");//setting edit text in fragment throws exception

Then in fragment class:

public class Myfragment extends Fragment {
    EditText edittext_fragment;

    public static Myfragment newInstance() {
        return new Myfragment();
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View myInflatedView = inflater.inflate(R.layout.Myfragment, container, false);
        InitializeFragment(myInflatedView);
        return myInflatedView;
    }

    private void InitializeFragment(View myInflatedView) {
        edittext_fragment = (EditText) myInflatedView.findViewById(R.id.edittext_fragment_caption);
    }

    public void set_fragment_editext(String value) {
        edittext_fragment.setText(value);
    }

}

Answer 1

oncreateview is called after you call the setText function, hence the null pointer.

Pass the string as an argument.

public class Myfragment extends Fragment { 
EditText edittext_fragment; 
String textViewText;

public static Myfragment newInstance(String textViewText){ 
this.textViewText = textViewText;
return new Myfragment(); 
} 

@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
View myInflatedView = inflater.inflate(R.layout.Myfragment, container, false);
InitializeFragment(myInflatedView); 
set_fragment_editext(textViewText);
return myInflatedView; 
} 

private void InitializeFragment(View myInflatedView) { 
edittext_fragment = (EditText) myInflatedView.findViewById(R.id.edittext_fragment_caption); 
} 
private void set_fragment_editext(String value) { 
edittext_fragment.setText(value); 
} 
}

Activity code:

Myfragment mFragment = Myfragment.newInstance("Hello World");

Answer 2

1) It takes some time to pass through fragment lifecycle.

2) It happens in the background.

Myfragment mFragment = new Myfragment();
fragmentTransaction.replace(R.id.fragment_container, mFragment);
fragmentTransaction.commit();

// EditText is not yet initialized
mFragment.set_fragment_editext("Hello world");//setting edit text in fragment throws exception

It is common android task that you should do some things only when some components are inittialized.

In your case you can do this in several ways:

1) Postpone string set.

class Myfragment extedns Fragment {
    private String mEditTextString;
    private EditText edittext_fragment;

    public void setEditText(String string) {
        mEditTextString = string;
        if (edittext_fragment != null) {
            edittext_fragment.setText(string);
        }
    }

    private void InitializeFragment(View myInflatedView) {
        edittext_fragment = (EditText) myInflatedView.findViewById(R.id.edittext_fragment_caption);
        if (mEditTextString != null) {
            edittext_fragment.setText(mEditTextString);
        }
    }
}

2) By callback to activity when edit text is inititlized. Please take a look at this guide https://developer.android.com/guide/components/fragments.html#CommunicatingWithActivity

3) As mentioned by @Karishnu Poddar if you want to set edit text just once you can pass it to fragment arguments