Null object reference in listview inside a custom alertdialog

Question

I have a custom layout for a alertdialog . Inside I have a listview . To open this alertdialog I have another list inside a fragment.

I have a error when I tap one item from the fragment listview .

If I take off the listview from the custom layout of the alertdialog , the alertdialog shows up; however, when I add it, the null object reference error occurs.

I tried to put all the my code inner onCreateView() but it is still failing.

BuildingFragment.java

public class BuildingFragment extends Fragment {


 public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    final Context context = getActivity().getBaseContext();
    final ListView listview2 = (ListView) getView().findViewById(R.id.listView3);

    listview2.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, final int position, long id) {

            // Get the layout inflater
            LayoutInflater inflater = getActivity().getLayoutInflater();

            AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
            builder.setView(inflater.inflate(R.layout.custom_dialog_building,null));


            ListView buildingLinkListView = (ListView) getActivity().findViewById(R.id.buildingLinkListView);
            ArrayList<BuildingLinkItem> buildingLinkList = new ArrayList<>();
            //....
            // Getting items for buildingLinkList
            //....

            BuildingLinkAdapter buildingLinkAdapter = new BuildingLinkAdapter(getActivity(),buildingLinkList);
            buildingLinkListView.setAdapter(buildingLinkAdapter);

            AlertDialog dialog = builder.create();
            dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
            dialog.show();

        }
    });

custom_dialog_building.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/customdialog"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="0dp">
<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/ic_bg_navigation"/>

<ListView
    android:id="@+id/buildingLinkListView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

And list_item_building_link.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp">
<ImageView
    android:layout_width="40dp"
    android:layout_height="40dp"
    android:id="@+id/list_item_building_icon"
    android:gravity="center"/>
<TextView
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:text="Large Text"
    android:id="@+id/list_item_building_text"
    android:gravity="center_vertical"
    android:layout_marginLeft="16dp"
    android:textSize="20sp"
    android:layout_toRightOf="@+id/list_item_building_icon" />

Please I need some support with this error.

Answer 1

Problem: You are getting NullPointerException just because you are trying to find ListView in an activity, not in a dialog view actually.

// Get the layout inflater
LayoutInflater inflater = getActivity().getLayoutInflater();
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
            builder.setView(inflater.inflate(R.layout.custom_dialog_building,null));           ListView buildingLinkListView = (ListView) getActivity().findViewById(R.id.buildingLinkListView);

Solution:

LayoutInflater inflater = getActivity().getLayoutInflater();
View view = inflater.inflate(R.layout.custom_dialog_building,null)

AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setView(view);

ListView buildingLinkListView = (ListView) view.findViewById(R.id.buildingLinkListView);

Answer 2

your problem lies here

AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setView(inflater.inflate(R.layout.custom_dialog_building,null));
ListView buildingLinkListView = (ListView) getActivity().findViewById(R.id.buildingLinkListView);

If I understand correcty the buildingLinkListView is part of the the dialog not of the Activity. Change it like:

AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
View view = null;
builder.setView(view = inflater.inflate(R.layout.custom_dialog_building,null));
ListView buildingLinkListView = (ListView) view.findViewById(R.id.buildingLinkListView);

I am assigning the inflated view in the setView call

setView(view = inflater.