为什么 getcontext() 仅在一种方法中为 null？
Why is getcontext() null only in one method?
你好，我在 Android Studio 的抽屉 activity 中制作了一个地图应用程序，一切都很顺利，直到我开始玩片段，因为我在 android 我真的不知道发生了什么或问题的原因是什么。
我用地图布局替换了主布局，使其成为我的 "home" 布局。然后我添加了一个片段，我可以在其中更改名为 "Configuration" 的应用程序的语言，并在抽屉菜单中按下 "Configuration" 按钮时调用该片段。
我注意到即使配置片段替换了地图布局，地图片段中的一些定位方法在后台仍然处于活动状态，我知道这是因为每次应用程序检查权限或更改时都会显示 Toast 消息location 我这样做是为了视觉辅助，所以我知道它的工作原理。
有 2 种情况，我的应用程序因同一行代码中的相同错误而崩溃，而它恰好是我作为帮助而放在那里的祝酒词之一。这对我来说很奇怪，因为显示消息后所有其他吐司都工作正常但是当它在 onLocationChanged 方法到达特定吐司时显示下一个错误：
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:114)
at android.widget.Toast.makeText(Toast.java:277)
at android.widget.Toast.makeText(Toast.java:267)
at com.tesseract.psiclops.zerov2.mapFragment.onLocationChanged(mapFragment.java:172)
at com.google.android.gms.internal.location.zzay.notifyListener(Unknown Source:4)
at com.google.android.gms.common.api.internal.ListenerHolder.notifyListenerInternal(Unknown Source:8)
at com.google.android.gms.common.api.internal.ListenerHolder$zza.handleMessage(Unknown Source:16)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
所以触发错误的两件事是：
1.- 当我按下后退按钮并且后台堆栈中没有片段（我想）所以它隐藏（关闭？最小化？）应用程序然后我再次打开它......它崩溃了。
2.- 当我进入配置片段并更改语言时。注意：我用来更改语言的方法会重新启动 activity，以便显示语言更改。
我想既然我关闭了应用程序，同时按下了后退按钮或调用了我的 languaje 方法，那么 getcontext() 在此之后变为 null 是有道理的，但为什么其他 toasts 显示消息并且只在那个时候崩溃具体路线？或具体方法？我该如何防止这种情况？？
注意：当我注释掉 toast 时，一切正常，没有崩溃或任何问题 :S，我真的需要了解发生了什么，这样我就可以防止以后出现任何问题。
地图片段：
public class mapFragment extends Fragment implements OnMapReadyCallback, LocationListener, GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener {
private GoogleMap mMap;
private GoogleApiClient mApiClient;
private Context mContext;
private OnFragmentInteractionListener mListener;
public mapFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_map, container, false);
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment)getChildFragmentManager()
.findFragmentById(R.id.map1);
mapFragment.getMapAsync(this);
}
private void SetSancrisM(final GoogleMap mMap) {
// Add a marker in Sancris and move the camera
// LatLng sancris = new LatLng(16.736380, -92.638795);
LatLngBounds SanCris = new LatLngBounds(new LatLng(16.720215, -92.684189), new LatLng(16.749950, -92.596649));
//mMap.addMarker(new MarkerOptions().position(sancris).title("Marker in Sancris"));
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(SanCris.getCenter(), 16));
//mMap.setLatLngBoundsForCameraTarget(SanCris);
}
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
mMap.getUiSettings().setZoomControlsEnabled(true);
try {
// Customise the styling of the base map using a JSON object defined
// in a raw resource file.
boolean success = googleMap.setMapStyle(
MapStyleOptions.loadRawResourceStyle(getContext(), R.raw.style_json));
if (!success) {
Toast.makeText(mContext, "Chido3", Toast.LENGTH_SHORT).show();
}
} catch (Resources.NotFoundException e) {
Toast.makeText(mContext, "No cargó el styla", Toast.LENGTH_SHORT).show();
}
//Calls the function that moves the cam to Sancris
SetSancrisM(mMap);
//Location permission conditions
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
Toast.makeText(mContext, "Failed to get location permission", Toast.LENGTH_SHORT).show();
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 200);
return;
} else {
if (!mMap.isMyLocationEnabled()) {
mMap.setMyLocationEnabled(true);
Toast.makeText(mContext, "Chido", Toast.LENGTH_SHORT).show();
}
}
mApiClient = new GoogleApiClient.Builder(getContext())
.addApi(LocationServices.API)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
mApiClient.connect();
}
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
switch (requestCode) {
case 200: {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
Toast.makeText(mContext, "Failed to get permission 2", Toast.LENGTH_SHORT).show();
} else {
mMap.setMyLocationEnabled(true);
Toast.makeText(mContext, "Chido2", Toast.LENGTH_SHORT).show();
}
}
}
}
}
@Override
public void onLocationChanged(Location location) {
if(location==null){
Toast.makeText(mContext, "No Location 4", Toast.LENGTH_SHORT).show();
}else{
LatLng ll= new LatLng(location.getLatitude(), location.getLongitude());
CameraUpdate update= CameraUpdateFactory.newLatLngZoom(ll,mMap.getCameraPosition().zoom);
mMap.animateCamera(update);
Toast.makeText(mContext, "Chido4", Toast.LENGTH_SHORT).show(); //This one right here is the one not working
}
}
LocationRequest mLocReq;
@Override
public void onConnected(@Nullable Bundle bundle) {
mLocReq = LocationRequest.create();
mLocReq.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
mLocReq.setInterval(1000);
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 200);
return;
}
LocationServices.FusedLocationApi.requestLocationUpdates(mApiClient, mLocReq, this);
Toast.makeText(mContext, "Chido5", Toast.LENGTH_SHORT).show();
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
}
//Este código tiene que ver con la comunicación entre fragmentos y actividades, osea déjalo para después
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
mContext=context;
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
在 onLocationChanged 方法中不起作用的 toast
@Override
public void onLocationChanged(Location location) {
if(location==null){
Toast.makeText(getContext(), "No Location 4", Toast.LENGTH_SHORT).show();
}else{
LatLng ll= new LatLng(location.getLatitude(), location.getLongitude());
CameraUpdate update= CameraUpdateFactory.newLatLngZoom(ll,mMap.getCameraPosition().zoom);
mMap.animateCamera(update);
Toast.makeText(getContext(), "Good4", Toast.LENGTH_SHORT).show(); //This one right here is the one not working
}
}
mapfragment 方法中的所有其他 toast 工作正常。
如果您需要更多代码，请在这里询问我，我会为您添加。非常感谢您！！
在片段中声明上下文变量
private Context mContext;
从 onAttach() 初始化它
@Override
public void onAttach(Context context) {
super.onAttach(context);
mContext = context;
}
你的祝酒词是
Toast.makeText(mContext,getString(R.string.toast) , Toast.LENGTH_LONG).show();
getContext() 只有 returns 当片段附加到其包含 Activity 时的非空值 - 在 onAttach() 和 onDetach() 之间。如果您在这些事件之外发生了回调，那么您就没有适当地清理您的听众。
您最早应该在 onAttach().
中创建监听器（即调用 requestLocationUpdates()）
然后您必须在 onDetach() 中注销您的侦听器（即调用 removeUpdates()），以防止泄漏您的 LocationListener 和整个 Fragment。
通常，您应该只在您的片段在屏幕上可见时才请求更新。在这种情况下，您将在 onStart() 中注册并在 onStop() 中注销。
你好，我在 Android Studio 的抽屉 activity 中制作了一个地图应用程序，一切都很顺利，直到我开始玩片段，因为我在 android 我真的不知道发生了什么或问题的原因是什么。
我用地图布局替换了主布局，使其成为我的 "home" 布局。然后我添加了一个片段，我可以在其中更改名为 "Configuration" 的应用程序的语言，并在抽屉菜单中按下 "Configuration" 按钮时调用该片段。
我注意到即使配置片段替换了地图布局，地图片段中的一些定位方法在后台仍然处于活动状态，我知道这是因为每次应用程序检查权限或更改时都会显示 Toast 消息location 我这样做是为了视觉辅助，所以我知道它的工作原理。
有 2 种情况，我的应用程序因同一行代码中的相同错误而崩溃，而它恰好是我作为帮助而放在那里的祝酒词之一。这对我来说很奇怪，因为显示消息后所有其他吐司都工作正常但是当它在 onLocationChanged 方法到达特定吐司时显示下一个错误：
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:114)
at android.widget.Toast.makeText(Toast.java:277)
at android.widget.Toast.makeText(Toast.java:267)
at com.tesseract.psiclops.zerov2.mapFragment.onLocationChanged(mapFragment.java:172)
at com.google.android.gms.internal.location.zzay.notifyListener(Unknown Source:4)
at com.google.android.gms.common.api.internal.ListenerHolder.notifyListenerInternal(Unknown Source:8)
at com.google.android.gms.common.api.internal.ListenerHolder$zza.handleMessage(Unknown Source:16)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
所以触发错误的两件事是：
1.- 当我按下后退按钮并且后台堆栈中没有片段（我想）所以它隐藏（关闭？最小化？）应用程序然后我再次打开它......它崩溃了。
2.- 当我进入配置片段并更改语言时。注意：我用来更改语言的方法会重新启动 activity，以便显示语言更改。
我想既然我关闭了应用程序，同时按下了后退按钮或调用了我的 languaje 方法，那么 getcontext() 在此之后变为 null 是有道理的，但为什么其他 toasts 显示消息并且只在那个时候崩溃具体路线？或具体方法？我该如何防止这种情况？？
注意：当我注释掉 toast 时，一切正常，没有崩溃或任何问题 :S，我真的需要了解发生了什么，这样我就可以防止以后出现任何问题。
地图片段：
public class mapFragment extends Fragment implements OnMapReadyCallback, LocationListener, GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener {
private GoogleMap mMap;
private GoogleApiClient mApiClient;
private Context mContext;
private OnFragmentInteractionListener mListener;
public mapFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_map, container, false);
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment)getChildFragmentManager()
.findFragmentById(R.id.map1);
mapFragment.getMapAsync(this);
}
private void SetSancrisM(final GoogleMap mMap) {
// Add a marker in Sancris and move the camera
// LatLng sancris = new LatLng(16.736380, -92.638795);
LatLngBounds SanCris = new LatLngBounds(new LatLng(16.720215, -92.684189), new LatLng(16.749950, -92.596649));
//mMap.addMarker(new MarkerOptions().position(sancris).title("Marker in Sancris"));
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(SanCris.getCenter(), 16));
//mMap.setLatLngBoundsForCameraTarget(SanCris);
}
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
mMap.getUiSettings().setZoomControlsEnabled(true);
try {
// Customise the styling of the base map using a JSON object defined
// in a raw resource file.
boolean success = googleMap.setMapStyle(
MapStyleOptions.loadRawResourceStyle(getContext(), R.raw.style_json));
if (!success) {
Toast.makeText(mContext, "Chido3", Toast.LENGTH_SHORT).show();
}
} catch (Resources.NotFoundException e) {
Toast.makeText(mContext, "No cargó el styla", Toast.LENGTH_SHORT).show();
}
//Calls the function that moves the cam to Sancris
SetSancrisM(mMap);
//Location permission conditions
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
Toast.makeText(mContext, "Failed to get location permission", Toast.LENGTH_SHORT).show();
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 200);
return;
} else {
if (!mMap.isMyLocationEnabled()) {
mMap.setMyLocationEnabled(true);
Toast.makeText(mContext, "Chido", Toast.LENGTH_SHORT).show();
}
}
mApiClient = new GoogleApiClient.Builder(getContext())
.addApi(LocationServices.API)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
mApiClient.connect();
}
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
switch (requestCode) {
case 200: {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
Toast.makeText(mContext, "Failed to get permission 2", Toast.LENGTH_SHORT).show();
} else {
mMap.setMyLocationEnabled(true);
Toast.makeText(mContext, "Chido2", Toast.LENGTH_SHORT).show();
}
}
}
}
}
@Override
public void onLocationChanged(Location location) {
if(location==null){
Toast.makeText(mContext, "No Location 4", Toast.LENGTH_SHORT).show();
}else{
LatLng ll= new LatLng(location.getLatitude(), location.getLongitude());
CameraUpdate update= CameraUpdateFactory.newLatLngZoom(ll,mMap.getCameraPosition().zoom);
mMap.animateCamera(update);
Toast.makeText(mContext, "Chido4", Toast.LENGTH_SHORT).show(); //This one right here is the one not working
}
}
LocationRequest mLocReq;
@Override
public void onConnected(@Nullable Bundle bundle) {
mLocReq = LocationRequest.create();
mLocReq.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
mLocReq.setInterval(1000);
if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 200);
return;
}
LocationServices.FusedLocationApi.requestLocationUpdates(mApiClient, mLocReq, this);
Toast.makeText(mContext, "Chido5", Toast.LENGTH_SHORT).show();
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
}
//Este código tiene que ver con la comunicación entre fragmentos y actividades, osea déjalo para después
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
mContext=context;
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
在 onLocationChanged 方法中不起作用的 toast
@Override
public void onLocationChanged(Location location) {
if(location==null){
Toast.makeText(getContext(), "No Location 4", Toast.LENGTH_SHORT).show();
}else{
LatLng ll= new LatLng(location.getLatitude(), location.getLongitude());
CameraUpdate update= CameraUpdateFactory.newLatLngZoom(ll,mMap.getCameraPosition().zoom);
mMap.animateCamera(update);
Toast.makeText(getContext(), "Good4", Toast.LENGTH_SHORT).show(); //This one right here is the one not working
}
}
mapfragment 方法中的所有其他 toast 工作正常。
如果您需要更多代码，请在这里询问我，我会为您添加。非常感谢您！！
在片段中声明上下文变量
private Context mContext;
从 onAttach() 初始化它
@Override
public void onAttach(Context context) {
super.onAttach(context);
mContext = context;
}
你的祝酒词是
Toast.makeText(mContext,getString(R.string.toast) , Toast.LENGTH_LONG).show();
getContext() 只有 returns 当片段附加到其包含 Activity 时的非空值 - 在 onAttach() 和 onDetach() 之间。如果您在这些事件之外发生了回调，那么您就没有适当地清理您的听众。
您最早应该在 onAttach().
requestLocationUpdates()）
然后您必须在 onDetach() 中注销您的侦听器（即调用 removeUpdates()），以防止泄漏您的 LocationListener 和整个 Fragment。
通常，您应该只在您的片段在屏幕上可见时才请求更新。在这种情况下，您将在 onStart() 中注册并在 onStop() 中注销。