我在调用Create报告时面临一个Null指针异常（它反过来调用它位于Activity内部的Asynctask“createReportTask”）但是应用程序崩溃在另一个片段的Asynsc任务（位于片段内）中给出了NPE，我试过了在构造函数中传递上下文等getContext（），getAcitivity（）等但都是徒劳的。我附上日志和代码请帮助!!
日志：
05-24 12:56:11.505 14632-14632/com.example.aiousecurityapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aiousecurityapplication, PID: 14632
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.widget.Toast.<init>(Toast.java:121)
at android.widget.Toast.makeText(Toast.java:291)
at android.widget.Toast.makeText(Toast.java:281)
at com.example.aiousecurityapplication.Activities.EventsReportFragment$MakeRequestTask.onPostExecute(EventsReportFragment.java:439)
at com.example.aiousecurityapplication.Activities.EventsReportFragment$MakeRequestTask.onPostExecute(EventsReportFragment.java:377)
at android.os.AsyncTask.finish(AsyncTask.java:727)
at android.os.AsyncTask.-wrap1(Unknown Source:0)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:744)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
创建报告代码：
public class CreateReport extends AppCompatActivity {
public EditText eventDate;
public EditText eventTime;
EditText reporterName;
EditText reporterCnic;
int flag = 0;
public static Calendar userCalendar;
private String Lat, Long;
private static final String[] BLOCK = new String[]{"Block 1", "Block 2", "Block 3", "Block 4", "Block 5"};
private static final String[] sampleDesc = new String[]{"Aag Lagi ha", "Darwaza Khula h", "Tala Ni Laga", "Lights / Fan On hain"};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_report);
Button createReport = (Button) findViewById(R.id.createReport);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
this.getSupportActionBar().setDisplayHomeAsUpEnabled(true);
final ActionBar ab = getSupportActionBar();
ab.setTitle("Create Report");
String myFormat1 = "yyyy-MM-dd";
String myFormat2 = "HH:mm";
SimpleDateFormat mainSdf1 = new SimpleDateFormat(myFormat1, Locale.US);
SimpleDateFormat mainSdf2 = new SimpleDateFormat(myFormat2, Locale.US);
Bundle bundle = getIntent().getExtras();
if (bundle != null) {
Lat = bundle.getString("lat");
Toast.makeText(getContext(), "Latitude" + Lat, Toast.LENGTH_LONG).show();
Long = bundle.getString("Long");
}
createReport.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (eventDescription.getText().toString().length() < 3) {
eventDescription.setError("Minimum 5 Letters");
Toast.makeText(getApplicationContext(),
"Please some Description", Toast.LENGTH_SHORT)
.show();
} else {
// creating new product in background thread
String blockname = blockName.getSelectedItem().toString().trim();
String eventEsc = eventEsclation.getSelectedItem().toString().trim();
String eventdesc = eventDescription.getText().toString().trim();
String cnic = reporterCnic.getText().toString().trim();
String userLat = Lat;
String userLong = Long;
String date = eventDate.getText().toString().trim();
String time = eventTime.getText().toString().trim();
new createReportTask().execute(blockname, eventEsc, eventdesc, cnic, userLat, userLong, date, time);
}
}
});
}
public class createReportTask extends AsyncTask<String, String, JSONObject> {
private JSONSenderReceiver jsonparser = new JSONSenderReceiver();
ProgressDialog pDialog;
@Override
protected void onPreExecute() {
super.onPreExecute();
Log.d("Creating Report", "in Pre Execute");
pDialog = new ProgressDialog(CreateReport.this);
pDialog.setMessage("Creating Report");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected void onPostExecute(JSONObject result) {
super.onPostExecute(result);
try {
if (result == null) {
pDialog.dismiss();
Toast.makeText(CreateReport.this, "No response from server.", Toast.LENGTH_SHORT).show();
return;
}
Log.d("Response from server: ", result.toString());
int success = Integer.parseInt(result.getString("status"));
String message = result.getString("message");
if (success == 2) {
Toast.makeText(CreateReport.this, message, Toast.LENGTH_SHORT).show();
}
pDialog.dismiss();
} catch (JSONException e) {
e.printStackTrace();
}
}
/**
* Creating product
*/
protected JSONObject doInBackground(String... args) {
String blockName = args[0] != null ? args[0] : "";
String eventEscalation = args[1];
String eventDesc = args[2];
String userCnic = args[3];
String userLat = args[4];
String userLong = args[5];
String date = args[6];
String time = args[7];
if (blockName.trim().length() != 0 && eventEscalation.trim().length() != 0
&& eventDesc.trim().length() != 0 && userCnic.trim().length() != 0 && userLat.trim().length() != 0
&& userLong.trim().length() != 0 && date.trim().length() != 0 && time.trim().length() != 0) {
//db field name in value side
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("page", "datasync"));
params.add(new BasicNameValuePair("blockName", blockName));
params.add(new BasicNameValuePair("eventEscalation", eventEscalation));
params.add(new BasicNameValuePair("eventDesc", eventDesc));
params.add(new BasicNameValuePair("userCnic", userCnic));
params.add(new BasicNameValuePair("userLat", userLat));
params.add(new BasicNameValuePair("userLong", userLong));
params.add(new BasicNameValuePair("date", date));
params.add(new BasicNameValuePair("time", time));
// getting JSON Object
// Note that create product url accepts POST method
return jsonparser.makeHttpRequest(AppConfig.URL_MAIN, "POST", params);
} else {
return null;
}
}
}
}
片段代码：
public class EventsReportFragment extends Fragment {
static final int REQUEST_AUTHORIZATION = 1001;
private RecyclerView recyclerView;
private static final int REQUEST_PERMISSIONS_REQUEST_CODE = 34;
private boolean mAlreadyStartedService = false;
private TextView mMsgView;
View rootView;
String latitude;
String longitude;
String myFormat1 = "yyyy-MM-dd";
String myFormat2 = "HH:mm:ss";
SimpleDateFormat mainSdf1 = new SimpleDateFormat(myFormat1, Locale.US);
SimpleDateFormat mainSdf2 = new SimpleDateFormat(myFormat2, Locale.US);
public EventsReportFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LocalBroadcastManager.getInstance(getContext()).registerReceiver(
new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
latitude = intent.getStringExtra(LocationMonitoringService.EXTRA_LATITUDE);
longitude = intent.getStringExtra(LocationMonitoringService.EXTRA_LONGITUDE);
new MakeRequestTask().execute(AppSettings.getUserCnic(), latitude, longitude,
mainSdf1.format(Calendar.getInstance().getTime()),
mainSdf2.format(Calendar.getInstance().getTime()));
if (latitude != null && longitude != null) {
mMsgView.setText("msg_location_service_started" + "\n Latitude : " + latitude + "\n Longitude: " + longitude);
}
}
}, new IntentFilter(LocationMonitoringService.ACTION_LOCATION_BROADCAST)
);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_events_list, container, false);
recyclerView = (RecyclerView) rootView.findViewById(R.id.recycler_view);
mMsgView = (TextView) rootView.findViewById (R.id.msgView);
FloatingActionButton fab = (FloatingActionButton) rootView.findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getActivity(), CreateReport.class);
intent.putExtra("lat", latitude);
intent.putExtra("long", longitude);
startActivity(intent);
}
});
return rootView;
}
@Override
public void onResume() {
super.onResume();
startStep1();
}
/**
* Step 1: Check Google Play services
*/
private void startStep1() {
//Check whether this user has installed Google play service which is being used by Location updates.
if (isGooglePlayServicesAvailable()) {
//Passing null to indicate that it is executing for the first time.
startStep2(null);
} else {
Toast.makeText(getContext(), "no_google_playservice_available", Toast.LENGTH_LONG).show();
}
}
/**
* Step 2: Check & Prompt Internet connection
*/
private Boolean startStep2(DialogInterface dialog) {
ConnectivityManager connectivityManager
= (ConnectivityManager) getActivity().getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
if (activeNetworkInfo == null || !activeNetworkInfo.isConnected()) {
promptInternetConnect();
return false;
}
if (dialog != null) {
dialog.dismiss();
}
if (checkPermissions()) { //Yes permissions are granted by the user. Go to the next step.
startStep3();
} else { //No user has not granted the permissions yet. Request now.
requestPermissions();
}
return true;
}
/**
* Show A Dialog with button to refresh the internet state.
*/
private void promptInternetConnect() {
AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
builder.setTitle("title_alert_no_intenet");
builder.setMessage("msg_alert_no_internet");
String positiveText = "Refresh Button";
builder.setPositiveButton(positiveText,
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
//Block the Application Execution until user grants the permissions
if (startStep2(dialog)) {
//Now make sure about location permission.
if (checkPermissions()) {
//Step 2: Start the Location Monitor Service
//Everything is there to start the service.
startStep3();
} else if (!checkPermissions()) {
requestPermissions();
}
}
}
});
AlertDialog dialog = builder.create();
dialog.show();
}
/**
* Step 3: Start the Location Monitor Service
*/
private void startStep3() {
//And it will be keep running until you close the entire application from task manager.
//This method will executed only once.
if (!mAlreadyStartedService && mMsgView != null) {
mMsgView.setText("Location_service_started");
//Start location sharing service to app server.........
Intent intent = new Intent(getContext(), LocationMonitoringService.class);
getActivity().startService(intent);
mAlreadyStartedService = true;
//Ends................................................
}
}
/**
* Return the availability of GooglePlayServices
*/
public boolean isGooglePlayServicesAvailable() {
GoogleApiAvailability googleApiAvailability = GoogleApiAvailability.getInstance();
int status = googleApiAvailability.isGooglePlayServicesAvailable(getContext());
if (status != ConnectionResult.SUCCESS) {
if (googleApiAvailability.isUserResolvableError(status)) {
googleApiAvailability.getErrorDialog(getActivity(), status, 2404).show();
}
return false;
}
return true;
}
/**
* Return the current state of the permissions needed.
*/
private boolean checkPermissions() {
int permissionState1 = ActivityCompat.checkSelfPermission(getContext(),
android.Manifest.permission.ACCESS_FINE_LOCATION);
int permissionState2 = ActivityCompat.checkSelfPermission(getContext(),
Manifest.permission.ACCESS_COARSE_LOCATION);
return permissionState1 == PackageManager.PERMISSION_GRANTED && permissionState2 == PackageManager.PERMISSION_GRANTED;
}
/**
* Start permissions requests.
*/
private void requestPermissions() {
boolean shouldProvideRationale =
ActivityCompat.shouldShowRequestPermissionRationale(getActivity(),
android.Manifest.permission.ACCESS_FINE_LOCATION);
boolean shouldProvideRationale2 =
ActivityCompat.shouldShowRequestPermissionRationale(getActivity(),
Manifest.permission.ACCESS_COARSE_LOCATION);
// Provide an additional rationale to the img_user. This would happen if the img_user denied the
// request previously, but didn't check the "Don't ask again" checkbox.
if (shouldProvideRationale || shouldProvideRationale2) {
Log.i(TAG, "Displaying permission rationale to provide additional context.");
showSnackbar(R.string.permission_rationale,
android.R.string.ok, new View.OnClickListener() {
@Override
public void onClick(View view) {
// Request permission
ActivityCompat.requestPermissions(getActivity(),
new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION},
REQUEST_PERMISSIONS_REQUEST_CODE);
}
});
} else {
Log.i(TAG, "Requesting permission");
// Request permission. It's possible this can be auto answered if device policy
// sets the permission in a given state or the img_user denied the permission
// previously and checked "Never ask again".
ActivityCompat.requestPermissions(getActivity(),
new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION},
REQUEST_PERMISSIONS_REQUEST_CODE);
}
}
/**
* Shows a {@link Snackbar}.
*
* @param mainTextStringId The id for the string resource for the Snackbar text.
* @param actionStringId The text of the action item.
* @param listener The listener associated with the Snackbar action.
*/
private void showSnackbar(final int mainTextStringId, final int actionStringId,
View.OnClickListener listener) {
Snackbar.make(
rootView.findViewById(android.R.id.content),
getString(mainTextStringId),
Snackbar.LENGTH_INDEFINITE)
.setAction(getString(actionStringId), listener).show();
}
/**
* Callback received when a permissions request has been completed.
*/
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
@NonNull int[] grantResults) {
Log.i(TAG, "onRequestPermissionResult");
if (requestCode == REQUEST_PERMISSIONS_REQUEST_CODE) {
if (grantResults.length <= 0) {
// If img_user interaction was interrupted, the permission request is cancelled and you
// receive empty arrays.
Log.i(TAG, "User interaction was cancelled.");
} else if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Log.i(TAG, "Permission granted, updates requested, starting location updates");
startStep3();
} else {
showSnackbar(R.string.permission_denied_explanation,
R.string.settings, new View.OnClickListener() {
@Override
public void onClick(View view) {
// Build intent that displays the App settings screen.
Intent intent = new Intent();
intent.setAction(
Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
Uri uri = Uri.fromParts("package",
BuildConfig.APPLICATION_ID, null);
intent.setData(uri);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
}
});
}
}
}
@Override
public void onDestroy() {
//Stop location sharing service to app server.........
getActivity().stopService(new Intent(getActivity(), LocationMonitoringService.class));
mAlreadyStartedService = false;
//Ends................................................
super.onDestroy();
}
public class MakeRequestTask extends AsyncTask<String, String, JSONObject> {
private Exception mLastError = null;
private JSONSenderReceiver jsonparser = new JSONSenderReceiver();
public MakeRequestTask() {
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected JSONObject doInBackground(String... args) {
try {
String cnic = args[0];
String userLat = args[1];
String userLong = args[2];
String date = args[3];
String time = args[4];
List<NameValuePair> params = new ArrayList<NameValuePair>();
if (cnic.trim().length() != 0 && userLat.trim().length() != 0
&& userLong.trim().length() != 0 && date.trim().length() != 0 && time.trim().length() != 0) {
params.add(new BasicNameValuePair("page", "locationUpdate"));
params.add(new BasicNameValuePair("cnic", cnic));
params.add(new BasicNameValuePair("userLat", userLat));
params.add(new BasicNameValuePair("userLong", userLong));
params.add(new BasicNameValuePair("date", date));
params.add(new BasicNameValuePair("time", time));
}
return jsonparser.makeHttpRequest(AppConfig.URL_MAIN, "POST", params);
} catch (Exception e) {
e.printStackTrace();
mLastError = e;
cancel(true);
return null;
}
}
@Override
protected void onPostExecute(JSONObject result) {
super.onPostExecute(result);
try {
if (result == null) {
Toast.makeText(getContext(), "No response from server.", Toast.LENGTH_SHORT).show();
return;
}
Log.d("Response from server: ", result.toString());
int success = Integer.parseInt(result.getString("status"));
String message = result.getString("message");
if (success == 1) {
Toast.makeText(getContext(), message, Toast.LENGTH_SHORT).show();
} else if (success == 2){
Toast.makeText(getContext(), message, Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
protected void onCancelled() {
}
}
}``
答案 0 :(得分：0)
在onPostExecute中，在执行任何工作之前检查活动是否正在运行。 因为如果活动不再运行，可能会调用onPostExecute
答案 1 :(得分：0)
试试这个
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_events_list, container, false);
LocalBroadcastManager.getInstance(getActivity()).registerReceiver(
new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
latitude = intent.getStringExtra(LocationMonitoringService.EXTRA_LATITUDE);
longitude = intent.getStringExtra(LocationMonitoringService.EXTRA_LONGITUDE);
new MakeRequestTask().execute(AppSettings.getUserCnic(), latitude, longitude,
mainSdf1.format(Calendar.getInstance().getTime()),
mainSdf2.format(Calendar.getInstance().getTime()));
if (latitude != null && longitude != null) {
mMsgView.setText("msg_location_service_started" + "\n Latitude : " + latitude + "\n Longitude: " + longitude);
}
}
}, new IntentFilter(LocationMonitoringService.ACTION_LOCATION_BROADCAST)
);
//your remaining code here
}
答案 2 :(得分：0)
使用以下行：
String message = result.optString("message");
// it will returns the empty string ("") if the key you specify doesn't exist
而不是使用
String message = result.getString("message");
// it will throws exception if the key you specify doesn't exist
答案 3 :(得分：0)
将getContext()替换为片段中的getActivity()
例如替换
Toast.makeText(getContext(), "no_google_playservice_available", Toast.LENGTH_LONG).show();
带
`Toast.makeText(getActivity(), "no_google_playservice_available", Toast.LENGTH_LONG).show();`
和
LocalBroadcastManager.getInstance(getContext()).registerReceiver(
带
LocalBroadcastManager.getInstance(getActivity()).registerReceiver(
依此类推。