Android 应用程序 - 尝试在空对象引用上调用接口方法“int java.util.List.size()" [英] Android app - Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
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问题描述
我正在创建一个在网格视图中显示电影海报的应用程序.我正在使用来自 themoviedb.org 的 API.问题是当我运行我的应用程序时出现以下错误并且我正在努力修复它:
I'm creating an app that display movie poster in a gridview. I'm using an API from themoviedb.org. The problem is I'm getting the follow error when I run my app and I'm struggling to fix it:
07-18 20:27:39.244 2751-2751/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.projmobileapp.pmdbadd.pmdb, PID: 2751
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.projmobileapp.pmdbadd.pmdb/com.projmobileapp.pmdbadd.pmdb.MainActivity}: android.view.InflateException: Binary XML file line #1: Error inflating class fragment
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2693)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5942)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
Caused by: android.view.InflateException: Binary XML file line #1: Error inflating class fragment
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:770)
at android.view.LayoutInflater.inflate(LayoutInflater.java:483)
at android.view.LayoutInflater.inflate(LayoutInflater.java:415)
at android.view.LayoutInflater.inflate(LayoutInflater.java:366)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:249)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:106)
at com.projmobileapp.pmdbadd.pmdb.MainActivity.onCreate(MainActivity.java:15)
at android.app.Activity.performCreate(Activity.java:6289)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5942)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
at android.widget.GridView.setAdapter(GridView.java:201)
at com.projmobileapp.pmdbadd.pmdb.MainActivityFragment.onCreateView(MainActivityFragment.java:53)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:924)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1116)
at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1218)
at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2170)
at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:300)
at android.support.v7.app.AppCompatDelegateImplV7.callActivityOnCreateView(AppCompatDelegateImplV7.java:838)
at android.support.v7.app.AppCompatDelegateImplV11.callActivityOnCreateView(AppCompatDelegateImplV11.java:34)
at android.support.v7.app.AppCompatDelegateImplV7.onCreateView(AppCompatDelegateImplV7.java:826)
at android.support.v4.view.LayoutInflaterCompatHC$FactoryWrapperHC.onCreateView(LayoutInflaterCompatHC.java:44)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:732)
at android.view.LayoutInflater.inflate(LayoutInflater.java:483)
at android.view.LayoutInflater.inflate(LayoutInflater.java:415)
at android.view.LayoutInflater.inflate(LayoutInflater.java:366)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:249)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:106)
at com.projmobileapp.pmdbadd.pmdb.MainActivity.onCreate(MainActivity.java:15)
at android.app.Activity.performCreate(Activity.java:6289)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5942)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
07-18 20:27:39.244 2702-2702/? W/ResourcesManager﹕ Asset path '/system/framework/twframework.jar' does not exist or contains no resources.
这是我的代码
package com.projmobileapp.pmdbadd.pmdb;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.GridView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
public class MainActivityFragment extends Fragment {
private ArrayList<Movie> flavorList;
public MainActivityFragment() {
}
MovieAdapter mMovieAdapter;
public void onSaveInstanceState(Bundle outState) {
outState.putParcelableArrayList("flavors", flavorList);
super.onSaveInstanceState(outState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
mMovieAdapter = new MovieAdapter(getActivity(), flavorList);
GridView listView = (GridView) rootView.findViewById(R.id.gridview_movie);
listView.setAdapter(mMovieAdapter);
updateMovie();
return rootView;
}
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
// Inflate the menu; this adds items to the action bar if it is present.
inflater.inflate(R.menu.mainactivityfragment, menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_refresh) {
updateMovie();
return true;
}
return super.onOptionsItemSelected(item);
}
private void updateMovie() {
FetchMovieTask movieTask = new FetchMovieTask();
movieTask.execute();
}
class FetchMovieTask extends AsyncTask<Void, Void, List<Movie>> {
private final String LOG_TAG = FetchMovieTask.class.getSimpleName();
@Override
protected List<Movie> doInBackground(Void... params) {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string.
String movieJsonStr = null;
try {
URL url = new URL("http://api.themoviedb.org/3/discover/movie?sort_by=popularity.desc&api_key=InsertAPIKey");
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line + "
");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
movieJsonStr = buffer.toString();
} catch (IOException e) {
Log.e(LOG_TAG, "Error ", e);
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
try {
return getMovieDataFromJson(movieJsonStr);
} catch (JSONException j) {
Log.e(LOG_TAG, "JSON Error", j);
}
return null;
}
private List<Movie> getMovieDataFromJson(String forecastJsonStr)
throws JSONException {
List<Movie> movies = new ArrayList<>();
JSONObject movieJson = new JSONObject(forecastJsonStr);
JSONArray movieArray = movieJson.getJSONArray("results");
for (int i = 0; i < movieArray.length(); i++) {
JSONObject movie = movieArray.getJSONObject(i);
Movie movie1 = new Movie(movieJson.getString("original_title"), movieJson.getDouble("vote_average"), movieJson.getString("release_date"), movieJson.getString("overview"), movieJson.getString("poster_path"));
movies.add(movie1);
}
return movies;
}
@Override
protected void onPostExecute(List<Movie> movies) {
if (movies != null) {
mMovieAdapter.clear();
for(Movie dayForecastStr : movies) {
mMovieAdapter.add(dayForecastStr);
}
// New data is back from the server. Hooray!
}
}
}
}
有人可以请教
推荐答案
我相信您应该将列表保存到 saveInstanceState 上的包中以进行轮换，您实际上并没有读回它在 onCreate 或 onCreateView 中，以防捆绑包不为空.另外，我什至不确定 Movie 是否真的是可打包的(使用 http://parcelabler.com )，但即使是这样，这也不起作用，因为您需要使用 writeTypedList 和 readTypedList 而不是 writeParcelableArrayList(即读取时返回 List，这不是您想要的).
I believe that you are supposedly saving the list out into the bundle on saveInstanceState for rotation, you're not actually reading it back in onCreate or onCreateView in case the bundle is not null. Also, I'm not even sure if Movie is actually a parcelable (use http://parcelabler.com ), but even if it were, this wouldn't work as you need to use writeTypedList and readTypedList and NOT writeParcelableArrayList (that returns List<Parcelable> on read, and that is NOT what you want).
但是当前的问题是你不应该在这一行给适配器一个 null :
But the current problem is that you should not give a null to the adapter in this line:
mMovieAdapter = new MovieAdapter(getActivity(), flavorList);
初始化适配器并仅在您实际有数据时才对其进行设置，或者使用空列表对其进行初始化.
Initialize the adapter and set it only when you actually have data, or initialize it with an empty list.
尽管如此，请使用writeTypedList 和readTypedList，否则以后保存状态时会遇到很多问题.
Really though, use writeTypedList and readTypedList, otherwise you'll run into a lot of issues later on with state saving.
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