Display two items in a ListView, getting setAdapter() on a null object reference

Question

I'm trying to create a ListView with two separate items of TextViews. My ListView is a part of content_main.xml (R.id.list), and TextViews are parts of list_item.xml (R.id.textUp, R.id.text2). The error that I get is a ListView.setAdapter(android.widget.ListAdapter)' on a null object reference. This is how were assigned hashmap and listView in my java code:

        private ListView list;
        private HashMap<String, String> associatedItem;

 protected void onCreate(Bundle savedInstanceState) {//LayoutInflater inflater
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_goal_text);
        list = findViewById(R.id.list);
        associatedItem = new HashMap<String, String>();
        ...

And the handler:

 public void doneButtonHandler(View view) {

    int   day  = picker.getDayOfMonth();
    int   month= picker.getMonth();
    int   year = picker.getYear();
    Calendar calendar = Calendar.getInstance();
    calendar.set(year,month,day);

    SimpleDateFormat sdf = new SimpleDateFormat("MM-dd-yyyy", US);
    String formatedDate = sdf.format(calendar.getTime());

    associatedItem.put(formatedDate, strMssg);

    ArrayList<HashMap<String, String>> listItems = new ArrayList<HashMap<String, String>>();

    Iterator it = associatedItem.entrySet().iterator();
    while (it.hasNext())
    {
        HashMap<String, String> resultsMap = new HashMap<>(2);
        Map.Entry pair = (Map.Entry)it.next();
        resultsMap.put("First Line",formatedDate);
        resultsMap.put("Second Line",strMssg);//pair.getValue().toString()
        listItems.add(resultsMap);
    }

    SimpleAdapter adapter = new SimpleAdapter(this, listItems ,R.layout.list_item,
            new String[]{"First Line", "Second Line"},
            new int[]{R.id.textUp, R.id.text2});

    list.setAdapter(adapter);
}

Error Logcat:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
        at com.example.gryzhuk.goaltracker.AddGoal.doneButtonHandler(AddGoal.java:134)

activity_add_goal_text.xml :

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".AddGoal"
    tools:layout_editor_absoluteY="81dp">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="28dp"
        android:layout_marginBottom="23dp"
        android:text="@string/enter_goal"
        android:textSize="20sp"

        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


    <Button
        android:onClick="nextButtonHandler"
        android:id="@+id/next_btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginBottom="53dp"
        android:text="@string/next_button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/enteredGoalTxt"
        app:layout_constraintVertical_bias="1.0" />

    <EditText
        android:id="@+id/enteredGoalTxt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="126dp"
        android:ems="10"
        android:hint="Enter here"
        android:inputType="textShortMessage"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

list_item.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView android:id="@+id/textUp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="@color/colorLineUp"
        android:textSize="21sp"
        android:textStyle="bold"
        />

    <TextView android:id="@+id/text2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="16sp"
        android:textColor="@color/colorLineBottom"
        android:textStyle="bold"
        />
</LinearLayout>

content_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".MainActivity"
    tools:showIn="@layout/activity_main">


    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:fab="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/activity_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingBottom="@dimen/activity_vertical_margin"
        tools:context="com.teamproblemsolver.fabsubmenu.MainActivity">

        <com.github.clans.fab.FloatingActionMenu
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_alignParentBottom="true"
            android:layout_marginLeft="10dp"
            android:layout_marginRight="10dp"
            android:layout_marginBottom="10dp"
            fab:menu_animationDelayPerItem="50"
            fab:menu_backgroundColor="@android:color/transparent"
            fab:menu_buttonSpacing="0dp"
            fab:menu_colorNormal="@color/colorPrimaryDark"
            fab:menu_colorPressed="#c784d3ed"
            fab:menu_colorRipple="#99FFFFFF"
            fab:menu_fab_hide_animation="@anim/hide_to_bottom"
            fab:menu_fab_show_animation="@anim/show_from_bottom"
            fab:menu_fab_size="normal"
            fab:menu_icon="@drawable/fab_add"
            fab:menu_openDirection="up"
            fab:menu_shadowColor="#66000000"
            fab:menu_shadowRadius="4dp"
            fab:menu_shadowXOffset="1dp"
            fab:menu_shadowYOffset="3dp"
            fab:menu_showShadow="true">


            <com.github.clans.fab.FloatingActionButton
                android:id="@+id/add_to_list"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:src="@drawable/ic_add_to_list"
                fab:fab_colorNormal="@color/colorPrimary"
                fab:fab_colorPressed="#c784d3ed"
                fab:fab_label="Add Goal"
                fab:fab_size="mini" />

        </com.github.clans.fab.FloatingActionMenu>

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



    </RelativeLayout>


</android.support.constraint.ConstraintLayout>

Answer 1

Double check the following method call:

setContentView(R.layout.activity_add_goal_text)

You said, that the list is in the content_main.xml but in your code there is no reference to that layout file. Did you want to use this in the call to setContentView? Or is that an included layout or a fragment?

Also, even though it's a bit more complicated to use than listview, recyclerview is the new way to go to display a list of items in Android.

Answer 2

Check this line in your view

associatedItem = new HashMap<String, String>();

and this one in your doneButtonHandler() method

ArrayList<HashMap<String, String>> listItems = new ArrayList<HashMap<String, String>>();

and in your adapter

SimpleAdapter adapter = new SimpleAdapter(this, listItems ,R.layout.list_item,
            new String[]{"First Line", "Second Line"},
            new int[]{R.id.textUp, R.id.text2});

so what listItems get here? if associatedItem has no items.

also make sure this is inflated in your view

 list = findViewById(R.id.list);

and check line 134 in your AddGoal.java and put debugger which will help you to find the problem.

As per your updated view the problem is with your list = findViewById(R.id.list); which is not inflated in your activity so list throws null object reference error which is set for adapter list.setAdapter(adapter) . Only solution is to change your implementation approach either inflate another view programmatically or modify your layout to use listview in your activity layout.

Answer 3

problem is setContentView(R.layout.activity_add_goal_text) you have't put listview in R.layout.activity_add_goal_text

that's why you are facing null pointer exception

put listview in R.layout.activity_add_goal_text

hope it works