任何人都可以帮忙解决这个问题吗？我想要的是将我的sqlite数据库中的数据显示到recyclerview中，但我收到了错误。
这是我的代码：
片段活动
public class pet_tab extends Fragment {
RecyclerView recyclerView;
Register_pet_database register_pet_database;
ArrayList<db_getItem> arrayList=new ArrayList<>();
Cursor cursor;
reg_Adapter reg_adapter;
public pet_tab() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view= inflater.inflate(R.layout.fragment_pet_tab, container, false);
recyclerView=(RecyclerView)view.findViewById(R.id.reg_pet_recycler);
loadDb();
return view;
}
public void loadDb(){
register_pet_database=new Register_pet_database(getActivity());
cursor=register_pet_database.queryData("select * from Pet_Registered");
if(cursor != null) {
if (cursor.moveToFirst()) {
do{
db_getItem item=new db_getItem();
item.setPet_name(cursor.getString(2));
item.setPet_type(cursor.getString(3));
item.setPet_breed(cursor.getString(4));
arrayList.add(item);
}while(cursor.moveToNext());
}
}
LinearLayoutManager linearLayoutManager=new LinearLayoutManager(getContext());
reg_adapter=new reg_Adapter(getActivity(),arrayList);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(linearLayoutManager);
recyclerView.setAdapter(reg_adapter);
}
}
我的适配器
package petguide.com.petguide101.database_item;
import android.app.Activity;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import petguide.com.petguide101.R;
/**
* Created by smartnote on 2/20/2017.
*/
public class reg_Adapter extends RecyclerView.Adapter<reg_ViewHolder>{
public Activity activity;
List<db_getItem> items= Collections.emptyList();
public reg_Adapter(Activity activity, List<db_getItem> items){
this.activity=activity;
this.items=items;
}
public reg_ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.reg_pet_recycler,parent,false);
return new reg_ViewHolder(view);
}
@Override
public void onBindViewHolder(reg_ViewHolder holder, int position) {
holder.pet_name.setText(items.get(position).getPet_name());
holder.pet_type.setText(items.get(position).getPet_type());
holder.pet_breed.setText(items.get(position).getPet_breed());
}
@Override
public int getItemCount() {
return items.size();
}
}
我的viewHolder
package petguide.com.petguide101.database_item;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.TextView;
import petguide.com.petguide101.R;
/**
* Created by smartnote on 2/20/2017.
*/
public class reg_ViewHolder extends RecyclerView.ViewHolder{
TextView pet_name;
TextView pet_type;
TextView pet_breed;
public reg_ViewHolder(View itemView) {
super(itemView);
pet_name=(TextView)itemView.findViewById(R.id.reg_pet_name);
pet_type=(TextView)itemView.findViewById(R.id.reg_pet_type);
pet_breed=(TextView)itemView.findViewById(R.id.reg_pet_breed);
}
}
**这是我在日志中得到的内容**
Process: petguide.com.petguide101, PID: 6857
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.query(java.lang.String, java.lang.String[])' on a null object reference
at petguide.com.petguide101.database.Register_pet_database.queryData(Register_pet_database.java:56)
at petguide.com.petguide101.pet_tab.loadDb(pet_tab.java:56)
at petguide.com.petguide101.pet_tab.onCreateView(pet_tab.java:44)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2189)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1299)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1528)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1595)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:757)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2355)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2146)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2098)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1979)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:626)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1268)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:668)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:630)
at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:611)
at android.support.design.widget.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:2178)
at android.support.design.widget.TabLayout.dispatchTabSelected(TabLayout.java:1155)
at android.support.design.widget.TabLayout.selectTab(TabLayout.java:1148)
at android.support.design.widget.TabLayout.selectTab(TabLayout.java:1118)
at android.support.design.widget.TabLayout$Tab.select(TabLayout.java:1413)
at android.support.design.widget.TabLayout$TabView.performClick(TabLayout.java:1523)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
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)