将 ArrayAdapter 设置为 GridView 适配器时，出现以下 NullPointerException。应用程序在运行时崩溃。
Logcat:
02-07 19:34:36.599: E/AndroidRuntime(26304): FATAL EXCEPTION: main
02-07 19:34:36.599: E/AndroidRuntime(26304): Process: com.shreyans.moviemania, PID: 26304
02-07 19:34:36.599: E/AndroidRuntime(26304): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.shreyans.moviemania/com.shreyans.moviemania.MainActivity}: android.view.InflateException: Binary XML file line #1: Error inflating class fragment
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2411)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2474)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.ActivityThread.access$800(ActivityThread.java:144)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1359)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.os.Handler.dispatchMessage(Handler.java:102)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.os.Looper.loop(Looper.java:155)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.ActivityThread.main(ActivityThread.java:5702)
02-07 19:34:36.599: E/AndroidRuntime(26304): at java.lang.reflect.Method.invoke(Native Method)
02-07 19:34:36.599: E/AndroidRuntime(26304): at java.lang.reflect.Method.invoke(Method.java:372)
02-07 19:34:36.599: E/AndroidRuntime(26304): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
02-07 19:34:36.599: E/AndroidRuntime(26304): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)
02-07 19:34:36.599: E/AndroidRuntime(26304): Caused by: android.view.InflateException: Binary XML file line #1: Error inflating class fragment
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:763)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.parseInclude(LayoutInflater.java:892)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.rInflate(LayoutInflater.java:802)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
02-07 19:34:36.599: E/AndroidRuntime(26304): at com.shreyans.moviemania.MainActivity.onCreate(MainActivity.java:17)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.Activity.performCreate(Activity.java:5958)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
02-07 19:34:36.599: E/AndroidRuntime(26304): ... 10 more
02-07 19:34:36.599: E/AndroidRuntime(26304): Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.widget.GridView.setAdapter(GridView.java:201)
02-07 19:34:36.599: E/AndroidRuntime(26304): at com.shreyans.moviemania.MainActivityFragment.onCreateView(MainActivityFragment.java:107)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1036)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1226)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1328)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2284)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentController.onCreateView(FragmentController.java:111)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:314)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:31)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:79)
02-07 19:34:36.599: E/AndroidRuntime(26304): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:733)
02-07 19:34:36.599: E/AndroidRuntime(26304): ... 21 more
这是我的适配器类:
public class MovieAdapter extends ArrayAdapter<Movie>{
private static final String LOG_TAG = MovieAdapter.class.getSimpleName();
public MovieAdapter(Activity context, List<Movie> movieList) {
super(context, 0, movieList);
}
@Override
public View getView(int position, View recycledView, ViewGroup parent) {
Movie movie = getItem(position);
if (recycledView == null){
recycledView = LayoutInflater.from(getContext()).inflate(
R.layout.grid_item_movies, parent, false);
}
ImageView imageView = (ImageView) recycledView.findViewById(R.id.grid_item_movies_image);
imageView.setAdjustViewBounds(true);
String baseUrl= "http://image.tmdb.org/t/p/";
final String SIZE="w185/";
Picasso.with(getContext())
.load(baseUrl + SIZE + movie.getPosterPath())
.into(imageView);
return recycledView;
}
}
MainActivityFragment.java:
public class MainActivityFragment extends Fragment {
private static final String LOG_TAG = "ServiceGenerator";
public static final String API_BASE_URL = "http://api.themoviedb.org/3/";
private String sortBy="popularity.desc"; //Default sorting order
private ArrayList<Movie> movieArrayList;
private MovieAdapter movieAdapter;
public MainActivityFragment() {
}
private void onLoadMoviesEvent() {
HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
// set your desired log level
logging.setLevel(HttpLoggingInterceptor.Level.BODY);
OkHttpClient httpClient = new OkHttpClient();
httpClient.interceptors().add(logging);
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(API_BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.client(httpClient)
.build();
MovieApiService movieApiService = retrofit.create(MovieApiService.class);
Call<MovieResults> call = movieApiService.fetchMovies(BuildConfig.MY_MOVIE_DB_API_KEY, sortBy);
call.enqueue(new Callback<MovieResults>(){
@Override
public void onResponse(Response<MovieResults> response, Retrofit retrofit1) {
MovieResults movieResults = response.body();
if (movieResults != null) {
Log.i(LOG_TAG, "Got requested object: " + movieResults.getTotalPages() + " results.");
movieArrayList = (ArrayList<Movie>) movieResults.getResults();
Log.i(LOG_TAG, "Retrieved arraylist with 1st movie: \n" +
"Name: " + movieArrayList.get(0).getTitle()+
"\nPoster path: " + movieArrayList.get(0).getPosterPath() +
"\nRelease Date: " + movieArrayList.get(0).getReleaseDate() +
"\nOverview: " + movieArrayList.get(0).getOverview());
movieAdapter.clear();
movieAdapter.addAll(movieArrayList);
}
else {
Log.e(LOG_TAG, "Getting null object of MovieResults");
try {
String string = response.errorBody().string();
Log.i(LOG_TAG, string);
}
catch (IOException e) {
Log.e(LOG_TAG, "IOException inside the response");
}
}
}
@Override
public void onFailure(Throwable throwable) {
Log.i(LOG_TAG, "Retrofit response failure");
}
});
}
@Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
movieAdapter = new MovieAdapter(getActivity(), movieArrayList);
GridView gridView = (GridView) rootView.findViewById(R.id.gridview);
gridView.setAdapter(movieAdapter);
onLoadMoviesEvent();
return rootView;
}
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
最佳答案
您正在使用异步请求来加载数据。因此，当您在 onCreateView() 中实例化适配器时方法中，您的数据尚未加载，并且 movieArrayList 为 null，这就是为什么在您创建适配器时它会抛出 NullPointerException。
1) 用空数组初始化数组列表，以避免 NPE:
private ArrayList<Movie> movieArrayList = new ArrayList<Movie>();
2) 调用 notifyDataSetChanged()从 onResponse() 更新数据后方法，刷新GridView :
@Override
public void onResponse(Response<MovieResults> response, Retrofit retrofit1) {
MovieResults movieResults = response.body();
if (movieResults != null) {
movieArrayList = (ArrayList<Movie>) movieResults.getResults();
movieAdapter.clear();// no need for this line in the first call
movieAdapter.addAll(movieArrayList);
movieAdapter.notifyDataSetChanged();
}
// ....
}
关于java - GridView setAdapter 方法给出 NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35254843/