列表视图适配器的空异常

Question

我在使用适配器实现自定义视图时遇到问题，代码没有显示任何错误，但是当我运行它时，它给了我一个空点异常。

 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

适配器的代码如下：

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;
 }
}

知道我为什么会收到这个错误吗？

编辑

指出错误的主要活动代码和我使用的信息。

        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) {

        }
    });

第 95 行特指这一行：

list.setAdapter(adapter);

Answer 1

看看你的代码：

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

适配器绝对不为空。
您在 setContentView() 中使用哪种布局？
确保布局有一个 id = list 的 ListView。如果您的跟踪是正确的，这是我能想到的唯一问题。

Answer 2

您显示的调用堆栈表明该错误位于ListFriendsMain 的某个位置。具体来说，如果您在以下位置显示代码会有所帮助：

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

Answer 3

据此，问题出在ListFriendsMain class in onCreate() 的行号95 中。 Caused by: java.lang.NullPointerException at friends.ListFriendsMain.onCreate(ListFriendsMain.java:95)

如果您可以使用相关代码编辑您的问题，那么您的问题就有可能得到准确解决。