用相同的方法为 Activity 和 SupportMapFragment 填充列表视图

Question

我用来自网络服务器的信息填充 ListView。在 Activity 中，我的 ListAdapeter 运行良好，但是当我尝试在 Fragment 中使用它时，我无法初始化我的适配器。

ListAdapter.java

public class ListAdapter extends BaseAdapter {

    MainActivity main;

    public ListAdapter(MainActivity main){
        this.main = main;
    }
    //Some methods.
}

MainActivity.java

public class ListReportsFragment extends SupportMapFragment {
    @Override
    public ListView list;
        public ListAdapter adapter;
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);
            //.........
            list = (ListView) findViewById(R.id.list);
            adapter = new ListAdapter(this);
            list.setAdapter(adapter);

        }
//........
    }

工作完美，但是，当我尝试在我的 Fragment 中使用它时：

ListReportsFragment

@Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        list = (ListView) getView().findViewById(R.id.list);
        adapter = new ListAdapter(new MainActivity());
        list.setAdapter(adapter); //This is the line 58
    }

我收到错误 java.lang.NullPointerExceptionlayout.ListReportsFragment.onActivityCreated(ListReportsFragment.java:58)

Answer 1

您正在创建 MainActivity 的新对象，这就是您收到错误的原因

adapter = new ListAdapter(new MainActivity());

将 MainActivity 传递给 fragment，然后将其传递给 ListAdapter

MainActivity main;

public ListReportsFragment(MainActivity main){
    this.main = main;
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    list = (ListView) getView().findViewById(R.id.list);
    adapter = new ListAdapter(main);
    list.setAdapter(adapter); //This is the line 58
}

Answer 2

改变

adapter = new ListAdapter(new MainActivity());

至

adapter = new ListAdapter(getActivity());

Answer 3

变化自

adapter = new ListAdapter(new MainActivity());

至

adapter = new ListAdapter(getActivity());

另外，将这部分代码移动到onCreateView()中，如下：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_main, container, false);

    adapter = new ListAdapter(getActivity());
    listView = (ListView) rootView.findViewById(R.id.listview_forecast);
    listView.setAdapter(arrayAdapter);

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//what to do on item click goes here!
    });
    return rootView;
}

用相同的方法为 Activity 和 SupportMapFragment 填充列表视图

Fill listview with the same method for Activity and SupportMapFragment

android

listview

android-fragments

supportmapfragment