问题
For some reason I am getting a null pointer exception pointing to videosFound when it is indeed not null. Even the parameter, adapter, that is being passed in is not null. I check and verify this simply by printing out if its null or not (both of them are NOT null). So can someone please tell me how I am getting this error?
private ListView videosFound;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_search);
searchInput = (EditText)findViewById(R.id.search_input);
videosFound = (ListView)findViewById(R.id.videos_found);
handler = new Handler();
addClickListener();
searchInput.setOnEditorActionListener(new TextView.OnEditorActionListener() {
@Override
public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
if (actionId == EditorInfo.IME_ACTION_DONE) {
searchOnYoutube(v.getText().toString());
return false;
}
return true;
}
});
}
private void updateVideosFound(){
ArrayAdapter<VideoItem> adapter = new ArrayAdapter<VideoItem>(getApplicationContext(), R.layout.video_item, searchResults){
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null){
convertView = getLayoutInflater().inflate(R.layout.video_item, parent, false);
}
ImageView thumbnail = (ImageView)convertView.findViewById(R.id.video_thumbnail);
TextView title = (TextView)convertView.findViewById(R.id.video_title);
TextView description = (TextView)convertView.findViewById(R.id.video_description);
VideoItem searchResult = searchResults.get(position);
Picasso.with(getApplicationContext()).load(searchResult.getThumbnailURL()).into(thumbnail);
title.setText(searchResult.getTitle());
description.setText(searchResult.getDescription());
return convertView;
}
};
if(videosFound == null){
System.out.println("videoFound is null***********");
}else{
System.out.println("videoFound is NOT null***********");
}
if(adapter == null){
System.out.println("adapter is null***********");
}else{
System.out.println("adapter is NOT null***********");
}
videosFound.setAdapter(adapter);//ERROR HERE. neither videosFound no adapter are null
}
private void addClickListener(){
videosFound.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> av, View v, int pos,
long id) {
Intent intent = new Intent(getApplicationContext(), PlayerActivity.class);
intent.putExtra("VIDEO_ID", searchResults.get(pos).getId());
startActivity(intent);
}
});
}
XML
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="@string/search"
android:id="@+id/search_input"
android:singleLine="true" />
<ListView
android:id="@+id/videos_found"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:dividerHeight="5dp" />
</LinearLayout>
Console:
03-24 18:04:31.833 17014-17440/com.example.shawn.myyoutube D/YC: Could not search: com.google.api.client.googleapis.json.GoogleJsonResponseException: 403 Forbidden
{
"code" : 403,
"errors" : [ {
"domain" : "usageLimits",
"message" : "There is a per-IP or per-Referer restriction configured on your API key and the request does not match these restrictions. Please use the Google Developers Console to update your API key configuration if request from this IP or referer should be allowed.",
"reason" : "ipRefererBlocked",
"extendedHelp" : "https://console.developers.google.com"
} ],
"message" : "There is a per-IP or per-Referer restriction configured on your API key and the request does not match these restrictions. Please use the Google Developers Console to update your API key configuration if request from this IP or referer should be allowed."
}
03-24 18:04:31.833 17014-17014/com.example.shawn.myyoutube I/System.out: videoFound is NOT null***********
03-24 18:04:31.833 17014-17014/com.example.shawn.myyoutube I/System.out: adapter is NOT null***********
03-24 18:04:31.843 17014-17014/com.example.shawn.myyoutube D/AndroidRuntime: Shutting down VM
03-24 18:04:31.843 17014-17014/com.example.shawn.myyoutube E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.shawn.myyoutube, PID: 17014
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.ListView.setAdapter(ListView.java:502)
at com.example.shawn.myyoutube.SearchActivity.updateVideosFound(SearchActivity.java:98)
at com.example.shawn.myyoutube.SearchActivity.access$200(SearchActivity.java:23)
at com.example.shawn.myyoutube.SearchActivity$2$1.run(SearchActivity.java:61)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5951)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
回答1:
In the stacktrace I see this:
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
The adapter is trying to call size() on a null List. Make sure your list searchResults is not null.
回答2:
NullPointerException occurred because searchResults is not initialized and is null.
Regarding your question in the comment -
do you know why the error did not actually point to the line where searchResults was?
ArrayAdapter calls getCount() internally whenever you call setAdapter() or refresh the already created adapter using notifyDataSetChanged().
Till you call setAdapter() or notifyDataSetChanged(), ArrayAdapter won't create view for you and in order to create that, it needs to check the size of the data which you passed to it.
For that it calls getCount()
which is
public int getCount() {
return mObjects.size();
}
where mObjects is initialized to the data list which you pass while creating your adapter.
Apparently mObjects.size() will throw NullPointerException since mObjects is null because searchResults is null.
Hope you understood.
来源：https://stackoverflow.com/questions/36212453/my-object-is-not-null-but-im-getting-a-null-pointer-exception