我是android应用开发人员中的漂亮菜鸟。我正在尝试打开创建一个电子书应用程序。该应用程序正在运行。但是，当我尝试打开下载片段时，发生此错误并且应用程序崩溃了！ 这是片段活动的Java代码- 包com.domain.app.Fragment;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.view.MenuItemCompat;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.SearchView;
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 com.loopj.android.http.*;
import com.domain.app.Activity.MainActivity;
import com.domain.app.Activity.Search;
import com.domain.app.Adapter.DownloadAdapter;
import com.domain.app.DataBase.DatabaseHandler;
import com.domain.app.Item.DownloadList;
import com.domain.app.R;
import com.domain.app.Util.Constant_Api;
import com.wang.avi.AVLoadingIndicatorView;
import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
public class DownloadFragment extends Fragment {
private RecyclerView recyclerView;
private AVLoadingIndicatorView progressBar;
private SwipeRefreshLayout mSwipeRefreshLayout;
private DownloadAdapter downloadAdapter;
public MenuItem searchItem;
private List<File> inFiles;
private List<DownloadList> downloadListsCompair;
private String root;
private DatabaseHandler db;
private ProgressDialog progressDialog;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = LayoutInflater.from(getActivity()).inflate(R.layout.category_fragment, container, false);
MainActivity.toolbar.setTitle(getResources().getString(R.string.download));
db = new DatabaseHandler(getActivity());
progressDialog = new ProgressDialog(getActivity());
inFiles = new ArrayList<>();
downloadListsCompair = new ArrayList<>();
root = Environment.getExternalStorageDirectory() + "/appName/";
mSwipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.swipeRefresh_category_fragment);
progressBar = (AVLoadingIndicatorView) view.findViewById(R.id.progressbar_category_fragment);
recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView_category_fragment);
progressBar.hide();
recyclerView.setHasFixedSize(true);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(layoutManager);
recyclerView.setFocusable(false);
mSwipeRefreshLayout.setColorSchemeResources(R.color.toolbar);
mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
new Execute().execute();
mSwipeRefreshLayout.setRefreshing(false);
}
});
new Execute().execute();
setHasOptionsMenu(true);
return view;
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.search_menu, menu);
searchItem = menu.findItem(R.id.ic_searchView);
SearchView searchView = (SearchView) MenuItemCompat.getActionView(searchItem);
searchView.setOnQueryTextListener((new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextSubmit(String query) {
startActivity(new Intent(getActivity(), Search.class)
.putExtra("search", query));
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
return true;
}
}));
MenuItemCompat.setOnActionExpandListener(searchItem,
new MenuItemCompat.OnActionExpandListener() {
@Override
public boolean onMenuItemActionCollapse(MenuItem item) {
// Do something when collapsed
return true; // Return true to collapse action view
}
@Override
public boolean onMenuItemActionExpand(MenuItem item) {
// Do something when expanded
return true; // Return true to expand action view
}
});
super.onCreateOptionsMenu(menu, inflater);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
// action with ID action_refresh was selected
default:
break;
}
return super.onOptionsItemSelected(item);
}
class Execute extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
progressDialog.show();
progressDialog.setMessage(getResources().getString(R.string.loading));
progressDialog.setCancelable(false);
Constant_Api.downloadLists.clear();
inFiles.clear();
downloadListsCompair.clear();
Constant_Api.db = new DatabaseHandler(getContext());
Constant_Api.downloadLists = Constant_Api.db.getDownload();
super.onPreExecute();
}
@Override
protected String doInBackground(String... strings) {
File file = new File(root);
getListFiles(file);
getDownloadLists(inFiles);
return null;
}
@Override
protected void onPostExecute(String s) {
downloadAdapter = new DownloadAdapter(getActivity(), downloadListsCompair);
recyclerView.setAdapter(downloadAdapter);
progressDialog.dismiss();
super.onPostExecute(s);
}
}
private List<File> getListFiles(File parentDir) {
// List<File> inFiles = new ArrayList<>();
Queue<File> files = new LinkedList<>();
files.addAll(Arrays.asList(parentDir.listFiles()));
while (!files.isEmpty()) {
File file = files.remove();
if (file.isDirectory()) {
files.addAll(Arrays.asList(file.listFiles()));
} else if (file.getName().endsWith(".epub") || file.getName().endsWith(".pdf")) {
inFiles.add(file);
}
}
return inFiles;
}
private List<DownloadList> getDownloadLists(List<File> list) {
for (int i = 0; i < Constant_Api.downloadLists.size(); i++) {
for (int j = 0; j < list.size(); j++) {
if (list.get(j).toString().contains(Constant_Api.downloadLists.get(i).getUrl())) {
downloadListsCompair.add(Constant_Api.downloadLists.get(i));
break;
} else {
if (j == list.size() - 1) {
db.deletePdf(Constant_Api.downloadLists.get(i).getId());
}
}
}
}
return downloadListsCompair;
}
}
这是我在Android Studio的“运行”窗口中看到的错误-
V/FA: Inactivity, disconnecting from the service
I/zygote: JIT allocated 56KB for compiled code of void android.view.View.<init>(android.content.Context, android.util.AttributeSet, int, int)
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #3
Process: com.domain.app, PID: 12493
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:353)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
at java.util.concurrent.FutureTask.run(FutureTask.java:271)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)
Caused by: java.lang.NullPointerException
at java.util.Objects.requireNonNull(Objects.java:203)
at java.util.Arrays$ArrayList.<init>(Arrays.java:3741)
at java.util.Arrays.asList(Arrays.java:3728)
at com.domain.app.Fragment.DownloadFragment.getListFiles(DownloadFragment.java:181)
at com.domain.app.Fragment.DownloadFragment.access$500(DownloadFragment.java:43)
at com.domain.app.Fragment.DownloadFragment$Execute.doInBackground(DownloadFragment.java:164)
at com.domain.app.Fragment.DownloadFragment$Execute.doInBackground(DownloadFragment.java:146)
at android.os.AsyncTask$2.call(AsyncTask.java:333)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)
E/RecyclerView: No adapter attached; skipping layout
V/FA: Recording user engagement, ms: 10252
V/FA: Connecting to remote service
V/FA: Activity paused, time: 4589154
D/FA: Logging event (FE): adunit_exposure(_xu), Bundle[{firebase_event_origin(_o)=am, ad_unit_id(_ai)=ca-app-pub-3940256099942544/6300978111, firebase_screen_class(_sc)=MainActivity, firebase_screen_id(_si)=751889283038278768, exposure_time(_xt)=9442}]
V/FA: Connection attempt already in progress
D/FA: Logging event (FE): ad_exposure(_xa), Bundle[{firebase_event_origin(_o)=am, firebase_screen_class(_sc)=MainActivity, firebase_screen_id(_si)=751889283038278768, exposure_time(_xt)=9442}]
V/FA: Connection attempt already in progress
D/FA: Logging event (FE): user_engagement(_e), Bundle[{firebase_event_origin(_o)=auto, engagement_time_msec(_et)=10252, firebase_screen_class(_sc)=MainActivity, firebase_screen_id(_si)=751889283038278768}]
V/FA: Connection attempt already in progress
Not logging ad unit exposure. No active activity
Not logging ad exposure. No active activity
D/EGL_emulation: eglMakeCurrent: 0xe62e4f20: ver 2 0 (tinfo 0xe624c000)
D/EGL_emulation: eglMakeCurrent: 0xe62e4f20: ver 2 0 (tinfo 0xe624c000)
D/EGL_emulation: eglMakeCurrent: 0xe62e4f20: ver 2 0 (tinfo 0xe624c000)
D/FA: Connected to remote service
V/FA: Processing queued up service tasks: 4
D/EGL_emulation: eglMakeCurrent: 0xe62e4f20: ver 2 0 (tinfo 0xe624c000)
D/EGL_emulation: eglMakeCurrent: 0xe62e4f20: ver 2 0 (tinfo 0xe624c000)
D/EGL_emulation: eglMakeCurrent: 0xe62e4f20: ver 2 0 (tinfo 0xe624c000)
E/WindowManager: android.view.WindowLeaked: Activity com.domain.app.Activity.MainActivity has leaked window DecorView@2ec76c[] that was originally added here
at android.view.ViewRootImpl.<init>(ViewRootImpl.java:485)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:346)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93)
at android.app.Dialog.show(Dialog.java:330)
at com.domain.app.Fragment.DownloadFragment$Execute.onPreExecute(DownloadFragment.java:150)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:648)
at android.os.AsyncTask.execute(AsyncTask.java:595)
at com.domain.app.Fragment.DownloadFragment.onCreateView(DownloadFragment.java:91)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2343)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1421)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1752)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1821)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:797)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2595)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2382)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2337)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2244)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:702)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
V/FA: Inactivity, disconnecting from the service
I/Ads: Ad is not visible. Not refreshing ad.
Scheduling ad refresh 60000 milliseconds from now.
I/Ads: Ad is not visible. Not refreshing ad.
Scheduling ad refresh 60000 milliseconds from now.
请帮助我找到实际的问题以及该错误的解决方案！预先感谢...：）