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29
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当我尝试从 AsyncTask 向我的 RecyclerView 设置数据时，我收到 NullPointerException。我尝试了很多方法，并且搜索了所有网络，阅读了许多 Stackoverflow 问题，但我仍然需要帮助。我是 Android 新手。
适配器:
public class DrugstoreAdapter extends RecyclerView.Adapter<DrugstoreAdapter.ViewHolder> {
private static final String TAG = "DrugstoreAdapter";
private List<Drugstore> drugstoreList;
private Context context;
public static class ViewHolder extends RecyclerView.ViewHolder {
private final TextView textView;
public ViewHolder(View v) {
super(v);
// Define click listener for the ViewHolder's View.
v.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "Element " + getAdapterPosition() + " clicked.");
}
});
textView = (TextView) v.findViewById(R.id.textView);
}
public TextView getTextView() {
return textView;
}
}
public DrugstoreAdapter(Context context, List<Drugstore> drugstoreList){
this.context = context;
this.drugstoreList = drugstoreList;
}
// Create new views (invoked by the layout manager)
@Override
public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
// Create a new view.
View v = LayoutInflater.from(viewGroup.getContext())
.inflate(R.layout.text_row_item, viewGroup, false);
return new ViewHolder(v);
}
@Override
public void onBindViewHolder(ViewHolder holder, final int position) {
Log.d(TAG, "Element " + position + " set.");
Drugstore drugstore = drugstoreList.get(position);
holder.textView.setText(drugstore.getTitle());
}
// Return the size of your dataset (invoked by the layout manager)
@Override
public int getItemCount() {
return drugstoreList.size();
}
}
fragment :
public class DrugstoreFragment extends Fragment {
private static final String TAG = "RecyclerViewFragment";
private static final String KEY_LAYOUT_MANAGER = "layoutManager";
private static final int SPAN_COUNT = 2;
private static final int DATASET_COUNT = 60;
private enum LayoutManagerType {
LINEAR_LAYOUT_MANAGER
}
protected LayoutManagerType mCurrentLayoutManagerType;
RecyclerView mRecyclerView;
protected CustomAdapter mAdapter;
protected RecyclerView.LayoutManager mLayoutManager;
protected DrugstoreAdapter drugstoreAdapter;
protected List<Drugstore> drugstoreList = new ArrayList<>();
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//initDataset();
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
//return inflater.inflate(R.layout.fragment_drugstore, container, false);
View rootView = inflater.inflate(R.layout.fg_recycler_view, container, false);
rootView.setTag(TAG);
mRecyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerView);
// LinearLayoutManager is used here, this will layout the elements in a similar fashion
// to the way ListView would layout elements. The RecyclerView.LayoutManager defines how
// elements are laid out.
mLayoutManager = new LinearLayoutManager(getActivity());
mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;
mRecyclerView.setLayoutManager(mLayoutManager);
/**
* NEW
*/
drugstoreAdapter = new DrugstoreAdapter(getActivity(), drugstoreList);
mRecyclerView.setAdapter(drugstoreAdapter);
return rootView;
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
initDataset();
}
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save currently selected layout manager.
savedInstanceState.putSerializable(KEY_LAYOUT_MANAGER, mCurrentLayoutManagerType);
super.onSaveInstanceState(savedInstanceState);
}
/**
* Generates Strings for RecyclerView's adapter. This data would usually come
* from a local content provider or remote server.
*/
private void initDataset() {
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
String email = "";
String type = "getDrugstores";
email = preferences.getString("email", null);
WorkInBackground wib = new WorkInBackground(getActivity());
wib.execute(type, email);
/*Drugstore drugstore = new Drugstore("F1");
drugstoreList.add(drugstore);
drugstore = new Drugstore("F2");
drugstoreList.add(drugstore);
drugstore = new Drugstore("F3");
drugstoreList.add(drugstore);
drugstore = new Drugstore("F4");
drugstoreList.add(drugstore);
drugstore = new Drugstore("F5");
drugstoreList.add(drugstore);
drugstoreAdapter.notifyDataSetChanged();*/
}
}
异步任务:
public class WorkInBackground extends AsyncTask<String, Void, String> {
private static final String TAG_SUCCESS = "success";
private static final String TAG_DRUGSTORE = "fornecedor";
Helper helper = new Helper();
SessionManager sessionManager;
ProgressDialog progressDialog;
Context context;
Intent goToMain;
private String type;
private String email;
private String ll;
int success;
private Drugstore drugstore = new Drugstore();
List<Drugstore> drugstoreList;
DrugstoreAdapter drugstoreAdapter;
protected RecyclerView mRecyclerView;
String ENCODING_UTF8 = "UTF-8";
String ENCODING_ISO = "iso-8859-1";
public static final int CONNECTION_TIMEOUT = 10000;
public static final int READ_TIMEOUT = 15000;
public static final String REQUEST_METHOD = "POST";
public WorkInBackground(Context context){
this.context = context;
progressDialog = new ProgressDialog(context);
sessionManager = new SessionManager(context);
goToMain = new Intent(context, MainActivity.class);
//mRecyclerView.setAdapter(new DrugstoreAdapter(context, drugstoreList));
}
@Override
protected String doInBackground(String... params) {
type = params[0];
if (type.equals("getDrugstores")) {
email = params[1];
try {
URL url = new URL(helper.link + helper.url_drugstores);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setReadTimeout(READ_TIMEOUT);
httpURLConnection.setConnectTimeout(CONNECTION_TIMEOUT);
httpURLConnection.setRequestMethod(REQUEST_METHOD);
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
/*OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, ENCODING_UTF8));
String postData = URLEncoder.encode("email", ENCODING_UTF8)+"="+URLEncoder.encode(email, ENCODING_UTF8);
bufferedWriter.write(postData);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();*/
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, ENCODING_ISO));
String result = "";
String line;
//String[] array = new String[0];
String[] myarray = new String[10];
int x = 0;
while ((line = bufferedReader.readLine()) != null) {
//result += line;
myarray[x] = line;
x++;
}
bufferedReader.close();
inputStream.close();
httpURLConnection.disconnect();
Log.d("WHERE: ", "RESULT " + result);
//JSONObject jsonObj = new JSONObject(result);
//JSONArray jsonArray = jsonObj.getJSONArray(TAG_DRUGSTORE);
//JSONArray jsonArray = result;
//JSONArray json = new JSONArray(result);
for (int i = 0; i < result.length(); i++) {
//JSONObject e = result.getChars(i);
String e = myarray[i];
Log.d("JSON: ", "" + e);
drugstore.setTitle(e);
drugstoreList = new ArrayList<>();
drugstoreList.add(drugstore);
}
//drugstoreAdapter.notifyDataSetChanged();
return result;
} catch (ProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
progressDialog.setCancelable(false);
progressDialog.setMessage("Loading...");
progressDialog.show();
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if (progressDialog.isShowing()) {
progressDialog.dismiss();
}
//mRecyclerView.setAdapter(drugstoreAdapter);
//mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);
mRecyclerView.setAdapter(new DrugstoreAdapter(this.context, drugstoreList));
//drugstoreAdapter.notifyDataSetChanged();
}
}
日志:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference
at br.unisinos.mobicine.classes.WorkInBackground.<init>(WorkInBackground.java:69)
at br.unisinos.mobicine.fragments.DrugstoreFragment.initDataset(DrugstoreFragment.java:114)
at br.unisinos.mobicine.fragments.DrugstoreFragment.onViewCreated(DrugstoreFragment.java:93)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:570)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1177)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1025)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:668)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:735)
at android.view.View.measure(View.java:18788)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1075)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452
编辑(新错误):
java.lang.RuntimeException: Unable to start activity ComponentInfo{br.unisinos.mobicine/br.unisinos.mobicine.activities.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference
at br.unisinos.mobicine.fragments.TabFragment.onCreateView(TabFragment.java:30)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:339)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:601)
at br.unisinos.mobicine.activities.MainActivity.onStart(MainActivity.java:77)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1237)
at android.app.Activity.performStart(Activity.java:6253)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
最佳答案
您没有在 WorkInBackground AsyncTask 中的任何地方实例化 mRecyclerView 并且您是这样声明它的:
protected RecyclerView mRecyclerView;
这意味着您要在此类中声明一个新字段，这意味着您没有使用在 Activity 中实例化的字段。您不需要在这里再次设置适配器:
mRecyclerView.setAdapter(new DrugstoreAdapter(this.context, drugstoreList));
您已经在 onCreateView 中完成了。只需将其从那里移除，它就不会崩溃。如果您想从 AsyncTask 中访问 mRecyclerView，只需将其传递到构造函数中(如果添加了新数据，则可能调用 notifyDataSetChanged .
关于android - AsyncTask RecyclerView NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38426736/
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