Question

我正在完成Google Android教程的一部分（准确地说是this part）而且我遇到了麻烦。我正在尝试将ListView的适配器设置为自定义ArrayAdapter。不幸的是，findViewById似乎返回null（这意味着我无法设置适配器）。

以下是相关代码：

MainActivityFragment

private final String LOG_TAG = MainActivityFragment.class.getSimpleName();
private ArtistItemAdapter artistsAdapter;

public MainActivityFragment() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_main, container, false);
    artistsAdapter = new ArtistItemAdapter(getActivity(), R.layout.list_item_artist, new Pager<Artist>().items);

    ListView artistsList = (ListView) rootView.findViewById(R.id.listViewArtists);
    artistsList.setAdapter(artistsAdapter);
    return rootView;
}

@Override
public void onStart() {
    EditText searchBar = (EditText) getView().findViewById(R.id.searchEditText);

    searchBar.setOnEditorActionListener(new TextView.OnEditorActionListener() {
        ArtistsPager artists;

        @Override
        public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
            boolean handled = false;
            if (actionId == EditorInfo.IME_ACTION_SEARCH) {
                FetchArtistsTask artistsTaskCall = new FetchArtistsTask();
                artistsTaskCall.execute(String.valueOf(v.getText()));
                handled = true;
            }
            return handled;
        }
    });
}

MainActivity.onCreate（）

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

fragment_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivityFragment">

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/searchEditText"
    android:inputType="textFilter"
    android:imeOptions="actionSearch"
    android:drawableLeft="@android:drawable/ic_menu_search"
    android:hint="Search Artist"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true" />

<ListView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/listViewArtists"
    android:layout_below="@+id/searchEditText"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />
</RelativeLayout>

activity_main.xml中

<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:id="@+id/fragment"
android:name="com.example.android.spotifyproject.MainActivityFragment"
tools:layout="@layout/fragment_main" android:layout_width="match_parent"
android:layout_height="match_parent" />

LogCat： http://pastebin.com/CUNF05Af

Answer 1

ListView不是null，它是您在创建时发送到适配器的数据，因此当您尝试在ListView上设置适配器时，它调用List.size（）关于数据（null），以及错误所在的位置。

为什么这个ListView为null？

1 个答案: