适用于listview的null异常

Question

I am having a problem implementing a custom view with an adapter, the code is not showing any error, but when I run it, it gives me a null point exception.

 01-08 12:21:43.949: E/AndroidRuntime(12646): FATAL EXCEPTION: main
 01-08 12:21:43.949: E/AndroidRuntime(12646): java.lang.RuntimeException: Unable to start    activity ComponentInfo{com.jp.blueoceans2/friends.ListFriendsMain}:  java.lang.NullPointerException
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1816)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1837)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.ActivityThread.access$1500(ActivityThread.java:132)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1033)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.os.Handler.dispatchMessage(Handler.java:99)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.os.Looper.loop(Looper.java:143)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.ActivityThread.main(ActivityThread.java:4196)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at java.lang.reflect.Method.invokeNative(Native Method)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at java.lang.reflect.Method.invoke(Method.java:507)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at dalvik.system.NativeStart.main(Native Method)
 01-08 12:21:43.949: E/AndroidRuntime(12646): Caused by: java.lang.NullPointerException
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at friends.ListFriendsMain.onCreate(ListFriendsMain.java:95)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1780)
 01-08 12:21:43.949: E/AndroidRuntime(12646):   ... 11 more

the code for the adapter is the follow:

public class FriendsAdapter extends BaseAdapter{

private Activity activity;
ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader; 

public FriendsAdapter (Activity a, ArrayList<HashMap<String, String>> d) {
    activity = a;
    data=d;
    inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    imageLoader=new ImageLoader(activity.getApplicationContext());
}

public int getCount() {
    return data.size();
}

public Object getItem(int position) {
    return position;
}

public long getItemId(int position) {
    return position;
}

public View getView(int position, View convertView, ViewGroup parent) {
    View vi=convertView;
    if(convertView==null)
        vi = inflater.inflate(R.layout.row_friend_cell, null);

    TextView surname_friend = (TextView)vi.findViewById(R.id.surname_friend);
    TextView name_friend = (TextView)vi.findViewById(R.id.name_friend);
    TextView relation = (TextView)vi.findViewById(R.id.relation);
    ImageView avatar = (ImageView)vi.findViewById(R.id.avatar);

    HashMap<String, String> friends = new HashMap<String, String>();
    friends = data.get(position);

    // Setting all values in listview
    surname_friend.setText(friends.get(ListFriendsMain.KEY_SURNAME));
    name_friend.setText(friends.get(ListFriendsMain.KEY_NAME));
    relation.setText(friends.get(ListFriendsMain.KEY_RELATION));
    imageLoader.DisplayImage(friends.get(ListFriendsMain.KEY_AVATAR_URL), avatar);
    return vi;
 }
}

any idea on why I am getting that error?

EDIT

the main activity code pointed on the error and the information that I used.

        XMLParser parser = new XMLParser();
    //HashMap<String, String> map = parser.getXmlFromUrl(URL, userid);
    String xml = parser.getXmlFromUrl(URL, userid);
    //Log.v("pictures", "string xml " + xml);
    Document doc = parser.getDomElement(xml); // getting DOM element
    NodeList nl = doc.getElementsByTagName(KEY_FRIEND);

    for (int i = 0; i < nl.getLength(); i++){
        HashMap<String, String> map = new HashMap<String, String>();
        Element e = (Element) nl.item(i);
        // adding each child node to HashMap key value
        map.put(KEY_ID, parser.getValue(e, KEY_ID));
        map.put(KEY_SURNAME, parser.getValue(e, KEY_SURNAME));
        map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
        map.put(KEY_RELATION, parser.getValue(e, KEY_RELATION));
        map.put(KEY_AVATAR_URL, parser.getValue(e, KEY_AVATAR_URL));

        // adding HashList to ArrayList
        info.add(map);
    }

    list=(ListView)findViewById(R.id.list);
    adapter = new FriendsAdapter(this, info);
    list.setAdapter(adapter);

    // Click event for single list row
    list.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {

        }
    });

line 95 specifically refers to this one:

list.setAdapter(adapter);

Answer 1

The call stack you've shown suggests the bug is somewhere in ListFriendsMain . Specifically, it would help if you show the code at:

friends.ListFriendsMain.onCreate(ListFriendsMain.java:95)

Answer 2

Having a look at your code:

list=(ListView)findViewById(R.id.list);
adapter = new FriendsAdapter(this, info);
list.setAdapter(adapter);

adapter is definitely not null.
Which layout do you use in setContentView()?
Make sure that layout has a ListView with an id = list. It is the only problem I can think of if your trace is correct.

Answer 3

The problem is in ListFriendsMain class in onCreate() at line number 95 according to this. Caused by: java.lang.NullPointerException at friends.ListFriendsMain.onCreate(ListFriendsMain.java:95)

If you can edit your question with your relevant code, there would be chances of having your problem solved exactly.