Android : getting NullPointerException for ImageView imag = (ImageView) findViewById(R.id.image)

Question

I am getting Null Pointer Exception for ImageView imag = (ImageView) findViewById(R.id.image). I have custome layout declared in R.layout.screen3 with custome list declared in R.layout.custom_row_screen3. Each row has few tasks and depending on their status an image is shown to right of each row.

Please guide me in getting this resolved as I am new to android.

here is my code below :::

public class screen3 extends ListActivity{
final ArrayList<HashMap<String, String>> list = new ArrayList<HashMap<String, String>>();
...
...
...
TextView tv;
ImageView imag;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.screen3);   
    System.out.println("Screen3");
    ...
    ...
    ...
    SimpleAdapter adapter = new SimpleAdapter(this, list,
            R.layout.custom_row_screen3,
            new String[] { "tname","schedule", "note", "time"}, new int[] { R.id.text1Screen3task,
                    R.id.text2Screen3task, R.id.text3Screen3task, R.id.text4Screen3task});
    populateList();
    setListAdapter(adapter);
}

public void populateList() {
    for(int i = 0; i <numberOfTasks; i++)
    {
        HashMap<String, String> h = new HashMap<String, String>();
        HashMap<String, String> hm = new HashMap<String, String>();
        h = tasks.get(i);
            ...
            ...     
        hm.put("tname", h.get("taskName"));
        hm.put("schedule", h.get("STime")+" - "+h.get("ETime"));

        if(h.get("taskStatus").trim().equals("1")){

            imag = (ImageView) findViewById(R.id.image);//   <<---- NULL RETURNED
            imag.setImageResource(R.drawable.done);
            ...
            ...
        }
        else{
            imag = (ImageView) findViewById(R.id.image);//  <<---- NULL RETURNED
            imag.setImageResource(R.drawable.not);
            ...
            ...
        }
        list.add(hm);
    }
    ...
    ... 
}

screen3 xml

<ListView android:id="@id/android:list" android:layout_width="fill_parent"
    android:layout_height="wrap_content" android:background="#000000"
    android:drawSelectorOnTop="false">
</ListView>

custom_row_screen3 xml

<LinearLayout android:orientation="vertical"
    android:layout_width="0dip" android:layout_weight="1"
    android:layout_height="wrap_content">

    <TextView android:id="@+id/text1Screen3task"
        android:layout_width="wrap_content" android:layout_height="0dip"
        android:layout_weight="1" android:textSize="21sp" android:textStyle="bold"
        android:gravity="clip_horizontal" />

    <TextView android:id="@+id/text2Screen3task"
        android:layout_width="wrap_content" android:layout_height="0dip"
        android:layout_weight="1" android:textSize="16sp" android:gravity="clip_horizontal" />

    <TextView android:id="@+id/text3Screen3task"
        android:layout_width="wrap_content" android:layout_height="0dip"
        android:layout_weight="1" android:textSize="16sp" android:gravity="clip_horizontal" />

    <TextView android:id="@+id/text4Screen3task"
        android:layout_width="wrap_content" android:layout_height="0dip"
        android:layout_weight="1" android:textSize="16sp" android:gravity="clip_horizontal" />
</LinearLayout>
<ImageView android:id="@+id/image" android:layout_width="wrap_content" android:paddingBottom="51dip"
    android:layout_height="wrap_content" android:layout_marginRight="16dip"
    />

Thanks Abhinav Tyagi

Answer 1

In short: You should write a ListAdapter which draws the views in the list. You seem to use findViewById() on the wrong view/context (on the screen3 xml layout). An example containing a ListAdapter is available at the android developer site.

The getView() method should basically look something like this:

public View getView(int position, View convertView, ViewGroup parent) {
    View v = convertView;
    if (convertView == null) {
        v = LayoutInflater.from(parent.getContext()).inflate(R.layout.row, null);
    }
    h = tasks.get(i);
    if(h.get("taskStatus").trim().equals("1")){
        imag = (ImageView) v.findViewById(R.id.image);
        imag.setImageResource(R.drawable.done);
    } else { 
        // ...
    }
    return v;
}

Answer 2

It seems that you haven't specified android:id="@+id/image" in the imageview inside your layout

Edit: I think the problem is you are using findViewById before the ListView in your ListActivity contains your custom_row which is who has the ImageView.

Try doing setListAdapter before populateList()

Answer 3

check whether the resource which your laoding is available in your res folder or not.

Answer 4

populateList() runs before the ListView is rendered to the screen, so the custom_row_screen3 doesn't exist in the Activity.

You could subclass SimpleAdapter and override getView() or setViewImage(), but I often find it simpler to anonymously implement a SimpleAdapter.ViewBinder and assign it with SimpleAdapter#setViewBinder().

In the ViewBinder, return false if the View that's passed in isn't an ImageView. If it is, you can use the map of data (passed in as an Object) to check the value of the "taskStatus" key.

Make sure to do this before calling setListAdapter().

adapter.setViewBinder(new SimpleAdapter.ViewBinder () {
  @Override
  boolean setViewValue(View view, Object data, String textRepresentation) {
    if (!(view instanceof ImageView)) return false;

    String taskStatus = ((Map<String, String>) data).get("taskStatus").trim();
    ((ImageView) view).setImageResource(taskStatus.equals("1") ? R.drawable.done :
                                                               R.drawable.not);
  }
});

Answer 5

Thanks all of you You all all pointed me in right direction that my imageview is not pointing to my adapter I followed the steps as in http://devblogs.net/2011/01/04/custom-listview-with-image-using-simpleadapter/ and it was working!!! just needed to put my image in hashmap... I was banging my head to the wall!!!