Android: ListView shows only first item. (Please refer image provided)

Question

I'm trying to retrieve data from firebase into an ArrayList and display the info on a ListView. I used a custom view, but for some reason, only the first record is being displayed. I double checked by displaying the details using Toast, and the other records are being shown there, but they aren't being displayed on ListView.

Android ListView only shows the first item

CustomAdapter.java

class CustomAdapter extends ArrayAdapter<String> {
    private int layout;
    public CustomAdapter(@NonNull Context context, int resource, @NonNull ArrayList<String> objects) {
        super(context, resource, objects);
        layout = resource;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        final String details = getItem(position);
        ViewHolder viewHolder;
        ViewHolder mainViewHolder = null;
        if(convertView == null){
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(layout, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.dealInfo = convertView.findViewById(R.id.dealinfo);
            viewHolder.accept = convertView.findViewById(R.id.accept);
            viewHolder.accept.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Toast.makeText(getContext(), details, Toast.LENGTH_SHORT).show();
                }
            });

            convertView.setTag(viewHolder);
        }else{
            mainViewHolder = (ViewHolder) convertView.getTag();
            mainViewHolder.dealInfo.setText(details);
        }

        return convertView;
    }
}

class ViewHolder{
    TextView dealInfo;
    Button accept;
}

My item Layout for ListView:

    <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout
        ...
        ..
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/dealinfo"
            android:layout_width="282dp"
            android:layout_height="wrap_content"
            android:fontFamily="monospace"
            android:textColor="#ffffff"
            android:textSize="15sp"
            android:textStyle="bold" />

        <Button
            android:id="@+id/accept"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignParentRight="true"
            android:layout_alignParentTop="true"
            android:layout_centerVertical="true"
            android:layout_toEndOf="@+id/dealinfo"
            android:background="#000000"
            android:text="Accept"
            android:textColor="#ffffff"
            android:textStyle="bold" />


    </RelativeLayout>

My ListView xml:

    <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:
    ...
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ManagerActivity">

    <TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:layout_alignParentTop="true"
        android:text="MANAGER"
        android:textAlignment="center"
        android:gravity="center"
        ..../>

    <ListView
        android:id="@+id/listview"
        android:layout_width="match_parent"
        android:layout_height="500dp"
        android:layout_below="@+id/title"
        android:layout_alignParentBottom="true"
        android:background="#1fa781"
        android:divider="#ffffff"
        android:dividerHeight="6dp">

    </ListView>


</RelativeLayout>

EDIT: I removed the else statement in getView() and its working now. Why so? This is what I did:

@NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        final String details = getItem(position);
        ViewHolder viewHolder;
        ViewHolder mainViewHolder = null;
        if(convertView == null){
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(layout, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.dealInfo = convertView.findViewById(R.id.dealinfo);
            viewHolder.accept = convertView.findViewById(R.id.accept);
            viewHolder.accept.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Toast.makeText(getContext(), details, Toast.LENGTH_SHORT).show();
                }
            });

            convertView.setTag(viewHolder);
        }
        {
            mainViewHolder = (ViewHolder) convertView.getTag();
            mainViewHolder.dealInfo.setText(details);
        }

        return convertView;
    }

Answer 1

Try this and tell me what happend

final String details = getItem(position);
    ViewHolder viewHolder;
    ViewHolder mainViewHolder = null;
    if(convertView == null){
        LayoutInflater inflater = LayoutInflater.from(getContext());
        //...
        //others codes
        //...
        ViewHolder.dealInfo.setText(details);//ADD THIS LINE
        convertView.setTag(viewHolder);
    }