In our app, the list of diaries should contains a diary picture followed by diary name, for which we are using custom class and custom adapter. But the app crashes.
//This is Word class (custom class)
public class Word
{
String dname;
public Word()
{
//default constructor
}
public Word(String dname) {
this.dname=dname;
}
/*public void setDiaryName(String dname)
{
this.dname=dname;
}*/
public String getDiaryName()
{
return dname;
}
}
//the custom adapter
public class ContentAdapter extends ArrayAdapter<Word>
{
Display d;
public ContentAdapter(Activity context, ArrayList<Word>title)
{
super(context, 0, title);
}
public View getView(int position, View convertView, ViewGroup parent) {
// Check if the existing view is being reused otherwise inflate the view
View listItemView = convertView;
if (listItemView == null) {
listItemView = LayoutInflater.from(getContext()).inflate(
R.layout.contents, parent, false);
}
Word w = getItem(position);
TextView mt = (TextView) listItemView.findViewById(R.id.exp);
mt.setText(w.getDiaryName());
mt.setVisibility(View.VISIBLE);
return listItemView;
}
}
//the fragment in which list of diaries is displayed
public class HistoryFragment extends Fragment
{
Word di;
ListView lv;
DatabaseReference reference;
FirebaseAuth mAuth = FirebaseAuth.getInstance();
Activity context;
public HistoryFragment(){
//default constructor
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState)
{
final View view = inflater.inflate(R.layout.scrolllist, container, false);
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("image").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//List<String> cities = new ArrayList<>();
final ArrayList<Word> cities = new ArrayList<>();
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String cityName = ds.getKey();
cities.add(new Word(cityName));
}
ListView listView = (ListView)view.findViewById(R.id.list_of_ds);
ContentAdapter arrayAdapter = new ContentAdapter(context,cities);
listView.setAdapter(arrayAdapter);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
//Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
uidRef.addListenerForSingleValueEvent(valueEventListener);
return view;
}
}
When the app is run, on selecting history fragment, the following error occurs - java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
//scrolllist.xml (for listview)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/drawable_gradient">
<ListView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/list_of_ds"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
</ListView>
<Button
android:id="@+id/add_images"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Add Images"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"/>
<Button
android:id="@+id/new_diary"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Diary?"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"/>
</RelativeLayout>
//contents.xml (the custom view of diary pic and diary name)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="88dp">
<ImageView
android:id="@+id/image_of_user"
android:layout_width="88dp"
android:layout_height="88dp"
android:src="@drawable/diarypic"
android:layout_marginTop="20dp"/>
<RelativeLayout
android:id="@+id/text_container"
android:layout_width="match_parent"
android:layout_height="88dp"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_toRightOf="@id/image_of_user"
android:orientation="vertical"
android:paddingLeft="16dp"
android:layout_marginTop="20dp">
<TextView
android:id="@+id/exp"
android:layout_width="match_parent"
android:layout_height="44dp"
android:layout_weight="1"
android:gravity="bottom"
android:textAppearance="?android:textAppearanceMedium"
android:textColor="@android:color/background_dark"
android:textStyle="bold"
android:text="lutti" />
</RelativeLayout>
</RelativeLayout>
</RelativeLayout>
