片段和列表视图

Question

I'm trying to use a ListView and Fragment.

My Code:

public static class ownFragment extends Fragment
{
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        MyListFragment test = new MyListFragment();
        test.makelist();
        return inflater.inflate(R.layout.whitelist_content, container, false);
    }

    public class MyListFragment extends ListFragment {

        private AdapterView.OnItemClickListener listener;


        public void makelist()
        {
            String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
                    "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
                    "Linux", "OS/2" };
            ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),
                    android.R.layout.simple_list_item_1, values);
            setListAdapter(adapter);
        }

        public void setOnItemClickListener(AdapterView.OnItemClickListener l) {
            this.listener = l;
        }

        @Override
        public void onListItemClick(ListView l, View v, int position, long id) {
            if(listener != null) {
                listener.onItemClick(l, v, position, id);
            }
        }

}

}

            public void clickme(View view){
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                .replace(R.id.content_frame, new ownFragment())
                .commit();
             }

but so i get a NullPointerException

enter code her07-26 22:57:46.709  19489-19489/de.anocom.ecp E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.NullPointerException
    at android.widget.ArrayAdapter.init(ArrayAdapter.java:310)
    at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:128)
    at de.anocom.ecp.MainActivity$Whitelist$MyListFragment.makelist(MainActivity.java:296)
    at de.anocom.ecp.MainActivity$ownFragment.onCreateView(MainActivity.java:282)
    at android.app.Fragment.performCreateView(Fragment.java:1695)
    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:885)
    at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
    at android.app.BackStackRecord.run(BackStackRecord.java:682)
    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441)
    at android.os.Handler.handleCallback(Handler.java:730)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:5103)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:525)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)e

Answer 1

First, you should not have the MyListFragment inner class. Make the outer class extend ListFragment and put all your list code there, and get rid of the inner class.

Second, getActivity() will return null if the fragment is not attached to an Activity yet (hence the NullPointerException). Most of the time I wait until onActivityCreated() callback to do anything with the Activity, such as initializing the adapter.

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(SavedInstanceState)
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, values);
    setListAdapter(adapter);
}