我有一个名为PopularFragment.java的片段，因为我从服务器获取图像，然后将它们显示在recyclerview中。通常它工作得很好，但有时应用程序崩溃与NullPointerException。
PopularFragment：
package com.apphics.minimalwallpapers;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.support.v4.app.Fragment;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import com.example.adapter.AdapterImage;
import com.example.item.ItemPhotos;
import com.example.util.Constant;
import com.example.util.DBHelper;
import com.example.util.EndlessRecyclerViewScrollListener;
import com.example.util.JsonUtils;
import com.pnikosis.materialishprogress.ProgressWheel;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
public class PopularFragment extends Fragment {
DBHelper dbHelper;
GridLayoutManager lLayout;
RecyclerView recyclerView;
AdapterImage adapterImage;
ArrayList<ItemPhotos> arrayOfLatestImage;
SwipeRefreshLayout mSwipeRefreshLayout;
ProgressWheel pbar;
TextView txt_no;
int spaceInPixels = 10;
Boolean isOver = false;
public PopularFragment newInstance() {
PopularFragment fragment = new PopularFragment();
return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_latest, container, false);
pbar=(ProgressWheel) rootView.findViewById(R.id.progressBar1);
mSwipeRefreshLayout = (SwipeRefreshLayout) rootView.findViewById(R.id.activity_main_swipe_refresh_layout);
mSwipeRefreshLayout.setColorSchemeResources(R.color.colorAccent);
dbHelper = new DBHelper(getActivity().getApplicationContext());
arrayOfLatestImage=new ArrayList<ItemPhotos>();
lLayout = new GridLayoutManager(getActivity(), 2);
lLayout.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
return adapterImage.isHeader(position) ? lLayout.getSpanCount() : 1;
}
});
recyclerView = (RecyclerView)rootView.findViewById(R.id.recyclerView_latest);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(lLayout);
recyclerView.addOnScrollListener(new EndlessRecyclerViewScrollListener(lLayout) {
@Override
public void onLoadMore(int p, int totalItemsCount) {
arrayOfLatestImage.add(null);
adapterImage.notifyItemInserted(arrayOfLatestImage.size() - 1);
arrayOfLatestImage.remove(arrayOfLatestImage.size() - 1);
adapterImage.notifyItemRemoved(arrayOfLatestImage.size());
if(!isOver) {
// list_url.clear();
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
new MyTask(getActivity().getApplicationContext()).execute(Constant.POPULAR_URL);
}
}, 2000);
} else {
adapterImage.hideHeader();
//Toast.makeText(getActivity(), "No more data", Toast.LENGTH_SHORT).show();
}
}
});
mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
refreshContent();
}
});
if (JsonUtils.isNetworkAvailable(getActivity())) {
new MyTask(getActivity().getApplicationContext()).execute(Constant.POPULAR_URL);
} else {
arrayOfLatestImage = dbHelper.getAllDataPopular("popular");
if(arrayOfLatestImage.size()==0) {
Toast.makeText(getActivity(), "Please connect to internet to load Images ", Toast.LENGTH_SHORT).show();
pbar.setVisibility(View.GONE);
} else {
adapterImage = new AdapterImage(getActivity(),arrayOfLatestImage);
recyclerView.setAdapter(adapterImage);
pbar.setVisibility(View.GONE);
}
}
return rootView;
}
private class MyTask extends AsyncTask<String, Void, String> {
private final WeakReference<Context> contextReference;
public MyTask(Context context) {
this.contextReference = new WeakReference<Context>(context);
}
@Override
protected void onPreExecute() {
super.onPreExecute();
Context context = this.contextReference.get();
if(context != null) {
if (arrayOfLatestImage.size() == 0) {
pbar.setVisibility(View.VISIBLE);
}
}
}
@Override
protected String doInBackground(String... params) {
return JsonUtils.getJSONString(params[0]);
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
Context context = this.contextReference.get();
if(context != null) {
if (arrayOfLatestImage.size() == 0) {
pbar.setVisibility(View.INVISIBLE);
}
if (null == result || result.length() == 0) {
Toast.makeText(getActivity(), "Something Went Wrong! Please check your internet and reload", Toast.LENGTH_SHORT).show();
} else {
try {
JSONObject mainJson = new JSONObject(result);
JSONArray jsonArray = mainJson.getJSONArray(Constant.TAG_ROOT);
if (jsonArray.length() <= arrayOfLatestImage.size() + 40) {
isOver = true;
}
int a = arrayOfLatestImage.size();
int b;
b = 40;
JSONObject objJson = null;
for (int i = a; i < a + b; i++) {
objJson = jsonArray.getJSONObject(i);
String id = objJson.getString(Constant.TAG_WALL_ID);
String cid = objJson.getString(Constant.TAG_CAT_ID);
String img = objJson.getString(Constant.TAG_WALL_IMAGE);
String img_thumb = objJson.getString(Constant.TAG_WALL_IMAGE_THUMB);
String cat_name = objJson.getString(Constant.TAG_CAT_NAME);
String views = objJson.getString(Constant.TAG_WALL_VIEWS);
ItemPhotos objItem = new ItemPhotos(id, cid, img, img_thumb, cat_name, views);
dbHelper.addtoFavorite(objItem, "popular");
arrayOfLatestImage.add(objItem);
}
} catch (JSONException e) {
e.printStackTrace();
isOver = true;
}
setAdapterToListview();
}
}
}
}
public void setAdapterToListview() {
if(arrayOfLatestImage.size()<41) {
adapterImage = new AdapterImage(getActivity(),arrayOfLatestImage);
recyclerView.setAdapter(adapterImage);
} else {
adapterImage.notifyDataSetChanged();
}
//setExmptTextView();
}
/*private void setExmptTextView() {
if(adapterImage.getItemCount()==0) {
txt_no.setVisibility(View.VISIBLE);
} else{
txt_no.setVisibility(View.INVISIBLE);
}
}*/
public void showToast(String msg) {
Toast.makeText(getActivity(), msg, Toast.LENGTH_LONG).show();
}
@Override
public void onResume() {
//if(adapterImage!=null && adapterImage.getItemCount() > 0) {
// adapterImage.notifyDataSetChanged();
//setExmptTextView();
// }
super.onResume();
}
private void refreshContent() {
// TODO implement a refresh
recyclerView.getRecycledViewPool().clear();
adapterImage.notifyDataSetChanged();
arrayOfLatestImage.clear();
try{
if (JsonUtils.isNetworkAvailable(getActivity())) {
new MyTask(getActivity()).execute(Constant.POPULAR_URL);
} else {
arrayOfLatestImage = dbHelper.getAllDataPopular("popular");
if(arrayOfLatestImage.size()==0) {
Toast.makeText(getActivity(), "First Time Load Application from Internet ", Toast.LENGTH_SHORT).show();
} else {
adapterImage = new AdapterImage(getActivity(),arrayOfLatestImage);
recyclerView.setAdapter(adapterImage);
}
}
} catch (IndexOutOfBoundsException e) {
e.printStackTrace();
}
mSwipeRefreshLayout.setRefreshing(false); // Disables the refresh icon
}
}
DBHelper.java：
package com.example.util;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.pm.PackageInfo;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import com.example.item.ItemAbout;
import com.example.item.ItemCategory;
import com.example.item.ItemGIF;
import com.example.item.ItemPhotos;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
public class DBHelper extends SQLiteOpenHelper {
private static String DB_NAME = "wallpaper.db";
private SQLiteDatabase db;
private final Context context;
private String DB_PATH;
String outFileName = "";
SharedPreferences.Editor spEdit;
public DBHelper(Context context) {
super(context, DB_NAME, null, 1);
this.context = context;
DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";
}
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
//------------------------------------------------------------
PackageInfo pinfo = null;
if (!dbExist) {
getReadableDatabase();
copyDataBase();
}
}
private boolean checkDataBase() {
File dbFile = new File(DB_PATH + DB_NAME);
return dbFile.exists();
}
private void copyDataBase() throws IOException {
InputStream myInput = context.getAssets().open(DB_NAME);
String outFileName = DB_PATH + DB_NAME;
OutputStream myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
// Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public Cursor getData(String Query) {
String myPath = DB_PATH + DB_NAME;
Cursor c = null;
try {
File file = new File(myPath);
if (file.exists() && !file.isDirectory())
db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
c = db.rawQuery(Query, null);
} catch (Exception e) {
Log.e("Err", e.toString());
}
return c;
}
//UPDATE temp_dquot SET age='20',name1='--',rdt='11/08/2014',basic_sa='100000',plno='814',pterm='20',mterm='20',mat_date='11/08/2034',mode='YLY',dab_sa='100000',tr_sa='0',cir_sa='',bonus_rate='42',prem='5276',basic_prem='5118',dab_prem='100.0',step_rate='for Life',loyal_rate='0',bonus_rate='42',act_mat='1,88,000',mly_b_pr='448',qly_b_pr='1345',hly_b_pr='2664',yly_b_pr='5276' WHERE uniqid=1
public void dml(String Query) {
String myPath = DB_PATH + DB_NAME;
File file = new File(myPath);
if (file.exists() && !file.isDirectory())
if (db == null)
db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
try {
db.execSQL(Query);
} catch (Exception e) {
Log.e("Error", e.toString());
}
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
public ArrayList<ItemPhotos> getAllData(String table){
ArrayList<ItemPhotos> arrayList = new ArrayList<ItemPhotos>();
Cursor cursor = getData("select * from '"+table+"'");
if(cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String pid = cursor.getString(cursor.getColumnIndex("pid"));
String cid = cursor.getString(cursor.getColumnIndex("cid"));
String cname = cursor.getString(cursor.getColumnIndex("cname"));
String img = cursor.getString(cursor.getColumnIndex("img"));
String img_thumb = cursor.getString(cursor.getColumnIndex("img_thumb"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemPhotos itemPhotos = new ItemPhotos(pid,cid,img,img_thumb,cname,views);
arrayList.add(itemPhotos);
cursor.moveToNext();
}
cursor.close();
}
return arrayList;
}
public ArrayList<ItemPhotos> getAllDataPopular(String table){
ArrayList<ItemPhotos> arrayList = new ArrayList<ItemPhotos>();
Cursor cursor = getData("select * from '"+table+"'");
if(cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String pid = cursor.getString(cursor.getColumnIndex("pid"));
String cid = cursor.getString(cursor.getColumnIndex("cid"));
String cname = cursor.getString(cursor.getColumnIndex("cname"));
String img = cursor.getString(cursor.getColumnIndex("img"));
String img_thumb = cursor.getString(cursor.getColumnIndex("img_thumb"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemPhotos itemPhotos = new ItemPhotos(pid,cid,img,img_thumb,cname,views);
arrayList.add(itemPhotos);
cursor.moveToNext();
}
cursor.close();
}
return arrayList;
}
public ArrayList<ItemPhotos> getAllDataShuffl(String table){
ArrayList<ItemPhotos> arrayList = new ArrayList<ItemPhotos>();
Cursor cursor = getData("select * from '"+table+"'");
if(cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String pid = cursor.getString(cursor.getColumnIndex("pid"));
String cid = cursor.getString(cursor.getColumnIndex("cid"));
String cname = cursor.getString(cursor.getColumnIndex("cname"));
String img = cursor.getString(cursor.getColumnIndex("img"));
String img_thumb = cursor.getString(cursor.getColumnIndex("img_thumb"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemPhotos itemPhotos = new ItemPhotos(pid,cid,img,img_thumb,cname,views);
arrayList.add(itemPhotos);
cursor.moveToNext();
}
cursor.close();
}
return arrayList;
}
public ArrayList<ItemGIF> getAllDataGIF(){
ArrayList<ItemGIF> arrayList = new ArrayList<ItemGIF>();
Cursor cursor = getData("select * from gif");
if(cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String gid = cursor.getString(cursor.getColumnIndex("gid"));
String img = cursor.getString(cursor.getColumnIndex("image"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemGIF itemGIF = new ItemGIF(gid,img,views);
arrayList.add(itemGIF);
cursor.moveToNext();
}
cursor.close();
}
return arrayList;
}
public ArrayList<ItemCategory> getAllDataCat(String table){
ArrayList<ItemCategory> arrayList = new ArrayList<ItemCategory>();
Cursor cursor = getData("select * from '"+table+"'");
if(cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String cid = cursor.getString(cursor.getColumnIndex("cid"));
String cname = cursor.getString(cursor.getColumnIndex("cname"));
String img = cursor.getString(cursor.getColumnIndex("img"));
String img_thumb = cursor.getString(cursor.getColumnIndex("img_thumb"));
String tot_wall = cursor.getString(cursor.getColumnIndex("tot_wall"));
ItemCategory itemCategory = new ItemCategory(cid,cname,img,img_thumb,tot_wall);
arrayList.add(itemCategory);
cursor.moveToNext();
}
cursor.close();
}
return arrayList;
}
public ArrayList<ItemPhotos> getFavRow(String id, String table)
{
ArrayList<ItemPhotos> dataList = new ArrayList<ItemPhotos>();
// Select All Query
String selectQuery = "SELECT * FROM '"+table+"' WHERE pid="+"'"+id+"'";
Cursor cursor = getData(selectQuery);
if (cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String pid = cursor.getString(cursor.getColumnIndex("pid"));
String cid = cursor.getString(cursor.getColumnIndex("cid"));
String cname = cursor.getString(cursor.getColumnIndex("cname"));
String img = cursor.getString(cursor.getColumnIndex("img"));
String img_thumb = cursor.getString(cursor.getColumnIndex("img_thumb"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemPhotos itemPhotos = new ItemPhotos(pid,cid,img,img_thumb,cname,views);
dataList.add(itemPhotos);
cursor.moveToNext();
}
cursor.close();
}
// return contact list
return dataList;
}
public ArrayList<ItemGIF> getFavRowGIF(String id)
{
ArrayList<ItemGIF> dataList = new ArrayList<ItemGIF>();
// Select All Query
String selectQuery = "SELECT * FROM gif WHERE gid="+"'"+id+"'";
Cursor cursor = getData(selectQuery);
if (cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String gid = cursor.getString(cursor.getColumnIndex("gid"));
String img = cursor.getString(cursor.getColumnIndex("image"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemGIF itemGIF = new ItemGIF(gid,img,views);
dataList.add(itemGIF);
cursor.moveToNext();
}
cursor.close();
}
// return contact list
return dataList;
}
public ArrayList<ItemPhotos> getCatList(String id, String table)
{
ArrayList<ItemPhotos> dataList = new ArrayList<ItemPhotos>();
// Select All Query
String selectQuery = "SELECT * FROM '"+table+"' WHERE cid="+"'"+id+"'";
Cursor cursor = getData(selectQuery);
if (cursor != null && cursor.getCount()>0) {
cursor.moveToFirst();
for (int i=0; i<cursor.getCount(); i++) {
String pid = cursor.getString(cursor.getColumnIndex("pid"));
String cid = cursor.getString(cursor.getColumnIndex("cid"));
String cname = cursor.getString(cursor.getColumnIndex("cname"));
String img = cursor.getString(cursor.getColumnIndex("img"));
String img_thumb = cursor.getString(cursor.getColumnIndex("img_thumb"));
String views = cursor.getString(cursor.getColumnIndex("views"));
ItemPhotos itemPhotos = new ItemPhotos(pid,cid,img,img_thumb,cname,views);
dataList.add(itemPhotos);
cursor.moveToNext();
}
cursor.close();
}
// return contact list
return dataList;
}
public void addtoFavorite(ItemPhotos itemPhotos, String table) {
dml("insert into '"+table+"' (pid,cid,cname,img,img_thumb,views) values ('"+itemPhotos.getId()+"','"+itemPhotos.getCatId()+"','"+itemPhotos.getCName()+"','"+itemPhotos.getImage()+"','"+itemPhotos.getImageThumb()+"','"+itemPhotos.getTotalViews()+"')");
}
public void addtoFavoriteGIF(ItemGIF itemGIF) {
dml("insert into gif (gid,image,views) values ('"+itemGIF.getId()+"','"+itemGIF.getImage()+"','"+itemGIF.getTotalViews()+"')");
}
public void addtoCatList(ItemCategory itemCategory, String table) {
dml("insert into '"+table+"' (cid,cname,img,img_thumb,tot_wall) values ('"+itemCategory.getId()+"','"+itemCategory.getName()+"','"+itemCategory.getImage()+"','"+itemCategory.getImageThumb()+"','"+itemCategory.getTotalWallpaper()+"')");
}
public void removeFav(String id) {
dml("delete from fav where pid = '"+id+"'");
}
public void removeFavGIF(String id) {
dml("delete from gif where gid = '"+id+"'");
}
public void updateView(String id, String totview) {
int views = Integer.parseInt(totview) + 1;
dml("update catlist set views = '"+String.valueOf(views)+"' where pid = '"+id+"'");
dml("update fav set views = '"+String.valueOf(views)+"' where pid = '"+id+"'");
dml("update latest set views = '"+String.valueOf(views)+"' where pid = '"+id+"'");
dml("update shuffl set views = '"+String.valueOf(views)+"' where pid = '"+id+"'");
}
public void updateViewGIF(String id, String totview) {
int views = Integer.parseInt(totview) + 1;
dml("update gif set views = '"+String.valueOf(views)+"' where gid = '"+id+"'");
}
public void addtoAbout() {
dml("delete from about");
dml("insert into about (name,logo,version,author,contact,email,website,desc,developed,privacy) values (" +
"'"+ Constant.itemAbout.getAppName()+"','"+ Constant.itemAbout.getAppLogo()+"','"+ Constant.itemAbout.getAppVersion()+"'" +
",'"+ Constant.itemAbout.getAuthor()+"','"+ Constant.itemAbout.getContact()+"','"+ Constant.itemAbout.getEmail()+"'" +
",'"+ Constant.itemAbout.getWebsite()+"','"+ Constant.itemAbout.getAppDesc()+"','"+ Constant.itemAbout.getDevelopedby()+"'" +
",'"+ Constant.itemAbout.getPrivacy()+"')");
}
public Boolean getAbout() {
String selectQuery = "SELECT * FROM about";
Cursor c = getData(selectQuery);
if (c != null && c.getCount()>0) {
c.moveToFirst();
for (int i=0; i<c.getCount(); i++) {
String appname = c.getString(c.getColumnIndex("name"));
String applogo = c.getString(c.getColumnIndex("logo"));
String desc = c.getString(c.getColumnIndex("desc"));
String appversion = c.getString(c.getColumnIndex("version"));
String appauthor = c.getString(c.getColumnIndex("author"));
String appcontact = c.getString(c.getColumnIndex("contact"));
String email = c.getString(c.getColumnIndex("email"));
String website = c.getString(c.getColumnIndex("website"));
String privacy = c.getString(c.getColumnIndex("privacy"));
String developedby = c.getString(c.getColumnIndex("developed"));
Constant.itemAbout = new ItemAbout(appname,applogo,desc,appversion,appauthor,appcontact,email,website,privacy,developedby);
}
c.close();
return true;
} else {
return false;
}
}
}
这是logcat：
java.lang.NullPointerException:
at com.example.util.DBHelper.<init>(DBHelper.java:35)
at com.example.adapter.AdapterImage.<init>(AdapterImage.java:69)
at com.apphics.minimalwallpapers.PopularFragment.setAdapterToListview(PopularFragment.java:226)
at com.apphics.minimalwallpapers.PopularFragment$MyTask.onPostExecute(PopularFragment.java:217)
at com.apphics.minimalwallpapers.PopularFragment$MyTask.onPostExecute(PopularFragment.java:141)
at android.os.AsyncTask.finish(AsyncTask.java:651)
at android.os.AsyncTask.access$500(AsyncTask.java:180)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5438)
at java.lang.reflect.Method.invoke(Native Method:0)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
答案 0 :(得分：0)
当arrayOfLatestImage.size()大于或等于41时抛出异常。在setAdapterToListview()函数的else块中初始化adapterImage。希望它有所帮助。