Question

您好，在下面的片段上单击我的列表视图，得到空指针。如果它是正常活动，则可以正常工作。它使我的应用程序崩溃了

任何人都可以帮助我在哪里弄错了。

public class HomeFragement extends Fragment {

    EditText et_building;
    TextView Add;
    ListView lv;
    ArrayList<String> arrayList;
    ArrayAdapter<String> adapter;



    public HomeFragement() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        ((NavigationViewActivity) getActivity()).setActionBarTitle("ADD BUILDING");

        View rootView = inflater.inflate(R.layout.activity_building, container, false);

        init();

        return rootView;
    }

    private void clickListener() {
        Add.setOnClickListener (new View.OnClickListener ( ) {
            @Override
            public void onClick(View v) {
                String result=et_building.getText ().toString ();
                arrayList.add (result);
                adapter.notifyDataSetChanged ();

            }
        });
    }

    private void init() {
        et_building=(EditText)getActivity ().findViewById (R.id.build_name);
        Add=(TextView)getActivity ().findViewById (R.id.addbuild);
        lv=(ListView)getActivity ().findViewById (R.id.list_building);
        arrayList=new ArrayList<String> ();
        adapter=new ArrayAdapter<String> (getActivity (),android.R.layout.simple_list_item_1,arrayList);
        lv.setAdapter(adapter);
        clickListener();
    }

Answer 1

发现问题-声明ID时出现问题。使用rootView代替getActivity()

这样做

    init(rootView);

这个方法应该是

private void init(View rootView ) {
        et_building=(EditText)rootView.findViewById (R.id.build_name);
        Add=(TextView)rootView.findViewById (R.id.addbuild);
        lv=(ListView)rootView.findViewById (R.id.list_building);
        arrayList=new ArrayList<String> ();
        adapter=new ArrayAdapter<String> (getActivity (),android.R.layout.simple_list_item_1,arrayList);
        lv.setAdapter(adapter);
        clickListener();
    }

Answer 2

尝试将您的init()代码放在onCreateView()内，例如：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    ((NavigationViewActivity) getActivity()).setActionBarTitle("ADD BUILDING");

    View rootView = inflater.inflate(R.layout.activity_building, container, false);

    et_building=(EditText)rootView.findViewById (R.id.build_name);
    Add=(TextView)rootView.findViewById (R.id.addbuild);
    lv=(ListView)rootView.findViewById (R.id.list_building);
    arrayList=new ArrayList<String> ();
    adapter=new ArrayAdapter<String> (getActivity(),android.R.layout.simple_list_item_1,arrayList);
    lv.setAdapter(adapter);

    return rootView;
}

并使用rootView代替getActivity()创建新对象

在Android中的空对象引用上的ListView.setAdapter（android.widget.ListAdapter）'

2 个答案: