我尝试启动我的应用程序，我可以看到我的片段正在加载，但每当我的适配器尝试将数据放入我的listview时，我的应用程序崩溃了。这是因为我的getActivity（）= null。现在我试着查一下，发现你必须OnAttach吗？但是我尝试了它，或者我做错了..它没有用，任何人都可以帮我恳求吗？
这是错误：
11-24 13:00:27.429: E/AndroidRuntime(31304): FATAL EXCEPTION: main
11-24 13:00:27.429: E/AndroidRuntime(31304): java.lang.NullPointerException
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.widget.ArrayAdapter.init(ArrayAdapter.java:310)
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:153)
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.laurenswuyts.witpa.ListEventAdapter.<init>(ListEventAdapter.java:23)
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.laurenswuyts.witpa.EventFragment.parseEventFromFQLResponse(EventFragment.java:154)
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.laurenswuyts.witpa.EventFragment$2.onCompleted(EventFragment.java:119)
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.facebook.Request$4.run(Request.java:1669)
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.os.Handler.handleCallback(Handler.java:615)
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.os.Handler.dispatchMessage(Handler.java:92)
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.os.Looper.loop(Looper.java:137)
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.app.ActivityThread.main(ActivityThread.java:4944)
11-24 13:00:27.429: E/AndroidRuntime(31304): at java.lang.reflect.Method.invokeNative(Native Method)
11-24 13:00:27.429: E/AndroidRuntime(31304): at java.lang.reflect.Method.invoke(Method.java:511)
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
11-24 13:00:27.429: E/AndroidRuntime(31304): at dalvik.system.NativeStart.main(Native Method)
这是我的主要活动：
public class EventFragment extends Fragment {
//Arraylist with event details
private static List<EventDetails> dataEvent;
//Adapter to put event details in listview
ListEventAdapter eventAdapter;
//Listview with the events
ListView lvEvents;
//To show Progress Circle
LinearLayout linearProgress;
private static final String TAG = "EventFragment";
private static final int REAUTH_ACTIVITY_CODE = 100;
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
}
@Override
public View onCreateView(LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.event,
container, false);
linearProgress = (LinearLayout) view.findViewById(R.id.linProgress);
lvEvents = (ListView) view.findViewById(R.id.lvEvent);
// Check for an open session
Session session = Session.getActiveSession();
if (session != null && session.isOpened()) {
// Get the user's data
ShowEventsFromFQL();
}
return view;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
uiHelper = new UiLifecycleHelper(getActivity(), callback);
uiHelper.onCreate(savedInstanceState);
}
public void ShowEventsFromFQL(){
// Check for an open session
Session session = Session.getActiveSession();
if (session != null && session.isOpened()) {
//Progressbar active
linearProgress.setVisibility(View.VISIBLE);
// Get the user's data
// ORDER BY attending_count DESC
String fqlQuery = ".....";
Bundle params = new Bundle();
params.putString("q", fqlQuery);
Session session2 = Session.getActiveSession();
Request request = new Request(session2,
"/fql",
params,
HttpMethod.GET,
new Request.Callback(){
public void onCompleted(Response response) {
Log.i(TAG, "Result: " + response.toString());
parseEventFromFQLResponse(response);
}
});
Request.executeBatchAsync(request);
}
}
public final void parseEventFromFQLResponse( Response response )
{
dataEvent = new ArrayList<EventDetails>();
try
{
GraphObject graphObj = response.getGraphObject();
JSONObject jsonObj = graphObj.getInnerJSONObject();
JSONArray jsonArr = jsonObj.getJSONArray( "data" );
for ( int i = 0; i < ( jsonArr.length() ); i++ )
{
JSONObject jObject = jsonArr.getJSONObject( i );
int attending_count = jObject.getInt("attending_count");
String name = jObject.getString("name");
String host = jObject.getString("host");
String description = jObject.getString("description");
String location = jObject.getString("location");
String start_time = jObject.getString("start_time");
String end_time = jObject.getString("end_time");
dataEvent.add(new EventDetails(attending_count, name, host, description, location, start_time, end_time));
}
// if(dataEvent != null){
if(getActivity() == null){
Log.i(TAG, "Result: loser" );
}
else {
Log.i(TAG, "Result: nope" );
}
eventAdapter = new ListEventAdapter(getActivity(), R.layout.event_item, dataEvent);
lvEvents.setAdapter(eventAdapter);
eventAdapter.notifyDataSetChanged();
//Progressbar gone
linearProgress.setVisibility(View.GONE);
// }
}
catch (JSONException e) {
e.printStackTrace();
}
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == REAUTH_ACTIVITY_CODE) {
uiHelper.onActivityResult(requestCode, resultCode, data);
}
}
private void onSessionStateChange(final Session session, SessionState state, Exception exception) {
if (session != null && session.isOpened()) {
// Get the user's data.
ShowEventsFromFQL();
}
}
private UiLifecycleHelper uiHelper;
private Session.StatusCallback callback = new Session.StatusCallback() {
@Override
public void call(final Session session, final SessionState state, final Exception exception) {
onSessionStateChange(session, state, exception);
}
};
@Override
public void onResume() {
super.onResume();
uiHelper.onResume();
}
@Override
public void onSaveInstanceState(Bundle bundle) {
super.onSaveInstanceState(bundle);
uiHelper.onSaveInstanceState(bundle);
}
@Override
public void onPause() {
super.onPause();
uiHelper.onPause();
}
@Override
public void onDestroy() {
super.onDestroy();
uiHelper.onDestroy();
}
}
提前致谢!!
答案 0 :(得分：0)
您在片段的onCreateView（）方法中做了很多工作。一旦片段创建其用户界面，Android就会调用onCreateView（）方法。我建议将执行异步部分的部分移动到onActiviyCreated（），例如：
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// Check for an open session
Session session = Session.getActiveSession();
if (session != null && session.isOpened()) {
// Get the user's data
ShowEventsFromFQL();
}
}
答案 1 :(得分：0)
我实际上没有挖掘源代码以确认这一点，但根据我的经验，当您从XML中膨胀片段或将其添加到活动的onCreate中时，getActivity()在onCreateView()之前无效。 }或onActivityCreated()。我通常不会使用onAttached()来表明getActivity()有效。