Access Fragment View from Activity's onCreate

问题

I am in the process of making my first app for Android, and I have a Fragment that gets added to my Activity in the Activity's onCreate() method. The problem I am facing is that I am unable to find any of the views contained within the Fragment from the Activity's onCreate() method.

Other threads have suggested that this is because the Fragment has not yet been inflated, so findViewById() will return null for any views contained within the Fragment.

Here is what I mean:

Activity:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    System.out.println("activity onCreate");
    setContentView(R.layout.activity_main);

    if (savedInstanceState != null) {
        return;
    }

    initialiseUI(); // Fragment added to Activity

    System.out.println("end of activity onCreate");
}

Fragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {
System.out.println("fragment onCreateView");
    return inflater.inflate(R.layout.event_log, container, false);
}

This prints the results:

activity onCreate end of activity onCreate fragment onCreateView

Because of this order, any attempt to access the views of the Fragment in the Activity's onCreate() method (using findViewById()) produces a NullPointerException, as the Fragment's onCreateView() only gets called AFTER the end of the Activity's onCreate().

Using the FragmentManger's executePendingTransactions() after adding the Fragment doesn't help.

Basically, I have been forced to put the problem code in the Activity's onStart() method instead of onCreate(), as onStart() happens AFTER the Fragment's onCreateView().

Does anyone what the standard practice here is, or how I can make my Fragment-View-accessing code work within the Activity's onCreate() method?

回答1:

Update your views in onCreateView().

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.event_log, container, false);
    TextView tv = (TextView) view.findViewById(R.id.text);
    tv.setText("hello world");
    return view;
}

Or if your changes depend on Activity your Fragment is attached to, use onActivityCreated().

@Override
public void onActivityCreated (Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    TextView tv = (TextView) getView().findViewById(R.id.text);
    tv.setText(getActivity.getSomeText());
}

来源：https://stackoverflow.com/questions/12122624/access-fragment-view-from-activitys-oncreate

标签

android

fragment

oncreate

findviewbyid