片段和列表视图

Question

我正在尝试使用ListView和Fragment。

我的代码：

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();
             }

但是我得到了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

首先，您不应具有MyListFragment内部类。 使外部类扩展ListFragment并将所有列表代码放在此处，并摆脱内部类。

其次，如果该片段尚未附加到Activity，则getActivity（）将返回null（因此为NullPointerException）。 大多数时候，我一直等到onActivityCreated（）回调对Activity进行任何操作，例如初始化适配器。

@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);
}