我试图制作一个用户可以登录并将用户数据保存到mysql-db的应用程序。 我使用PreferenceActivity和PreferenceFragment来处理这个问题。通常情况下，这可以正常工作，直到我改变用户...
现在，当用户A注销并且用户B登录时，会发生错误。（在注销时，使用clear（）。和commit（）清除共享首选项。）
应用程序停止
java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File android.content.Context.getCacheDir()'
on a null object reference
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java: 43)
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java: 78)
at com.jamp.jamp.UserProfileSettingsFragment.onSharedPreferenceChanged(UserProfileSettingsFragment.java: 171)
at android.app.SharedPreferencesImpl$EditorImpl.notifyListeners(SharedPreferencesImpl.java: 479)
at android.app.SharedPreferencesImpl$EditorImpl.apply(SharedPreferencesImpl.java: 387)
at android.preference.Preference.tryCommit(Preference.java: 1415)
at android.preference.Preference.persistString(Preference.java: 1448)
at android.preference.EditTextPreference.setText(EditTextPreference.java: 94)
at android.preference.EditTextPreference.onDialogClosed(EditTextPreference.java: 148)
at android.preference.DialogPreference.onDismiss(DialogPreference.java: 395)
at android.app.Dialog$ListenersHandler.handleMessage(Dialog.java: 1337)
at android.os.Handler.dispatchMessage(Handler.java: 102)
at android.os.Looper.loop(Looper.java: 154)
at android.app.ActivityThread.main(ActivityThread.java: 6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java: 756)
现在这是片段的代码
package com.jamp.jamp;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.Preference;
import android.preference.PreferenceFragment;
import android.preference.PreferenceManager;
import android.support.v7.app.AlertDialog;
import android.widget.Toast;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.Volley;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.util.HashMap;
/**
* Created by Erikken on 05.09.2017.
*/
public class UserProfileSettingsFragment extends PreferenceFragment implements SharedPreferences.OnSharedPreferenceChangeListener {
SessionManager session;
SharedPreferences prefs;
String prefs_realname;
String prefs_email;
String prefs_streetname;
String prefs_postcode;
String prefs_city;
String prefs_state;
@Override
public void onCreate(final Bundle savedInstanceState) {
prefs = this.getActivity().getSharedPreferences("JampSharedPrefs", Context.MODE_PRIVATE);
final SharedPreferences.Editor editor = prefs.edit();
PreferenceManager.getDefaultSharedPreferences(getActivity()).registerOnSharedPreferenceChangeListener(this);
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.usersettings);
session = new SessionManager(this.getActivity().getApplicationContext());
HashMap < String, String > user = session.getUserDetails();
final String sessionUsername = user.get(SessionManager.KEY_USERNAME);
// ResponseListener um Request Nutzerdaten auszulesen.
Response.Listener < String > UserDataResponseListener = new Response.Listener < String > () {
@Override
public void onResponse(String response) {
try {
JSONObject jsonResponse = new JSONObject(response);
boolean success = jsonResponse.getBoolean("success");
// Wenn Datenabfrage erfolgreich, JSONResponse auswerten. // If successful, import data from mysql database
if (success) {
String responseRealName = jsonResponse.getString("realname");
if (responseRealName.equals("")) {
responseRealName = getResources().getString(R.string.MissingRealName);
}
String responseEmail = jsonResponse.getString("email");
if (responseEmail.equals("")) {
responseEmail = getResources().getString(R.string.MissingEmail);
}
String responseStreetName = jsonResponse.getString("streetname");
if (responseStreetName.equals("")) {
responseStreetName = getResources().getString(R.string.MissingStreetName);
}
String responsePostcode = jsonResponse.getString("postcode");
if (responsePostcode.equals("")) {
responsePostcode = getResources().getString(R.string.MissingPostcode);
}
String responseCity = jsonResponse.getString("city");
if (responseCity.equals("")) {
responseCity = getResources().getString(R.string.MissingCity);
}
String responseState = jsonResponse.getString("state");
if (responseState.equals("")) {
responseState = getResources().getString(R.string.MissingState);
}
int responseAge = jsonResponse.getInt("age");
int responseIsPremium = jsonResponse.getInt("isPremium"); // BOOLEAN
// Add data to shared prefs
editor.putString("realname", responseRealName);
editor.putString("email", responseEmail);
editor.putString("streetname", responseStreetName);
editor.putString("postcode", responsePostcode);
editor.putString("city", responseCity);
editor.putString("state", responseState);
editor.commit();
prefs_realname = prefs.getString("realname", "");
prefs_email = prefs.getString("email", "");
prefs_streetname = prefs.getString("streetname", "");
prefs_postcode = prefs.getString("postcode", "");
prefs_city = prefs.getString("city", "");
prefs_state = prefs.getString("state", "");
Preference prefUserData = (Preference) findPreference("preferencescreen_userdata");
prefUserData.setTitle(sessionUsername);
prefUserData.setSummary(prefs_realname + "\n" +
prefs_email + "\n" +
prefs_streetname + "\n" +
prefs_postcode + " " + prefs_city + "\n" +
prefs_state);
findPreference("settings_username").setTitle(sessionUsername);
findPreference("settings_realname").setSummary(prefs_realname);
findPreference("settings_email").setSummary(prefs_email);
findPreference("settings_streetname").setSummary(prefs_streetname);
findPreference("settings_postcode").setSummary(prefs_postcode);
findPreference("settings_city").setSummary(prefs_city);
findPreference("settings_state").setSummary(prefs_state);
} else {
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage("Konnte Nutzerdaten nicht abrufen.")
.setNegativeButton("Nochmal", null)
.create()
.show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
// Request an userdatarequest.php senden / Send request to userdatarequest.php
UserDataRequest userDataRequest = new UserDataRequest(sessionUsername, UserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(this.getActivity());
queue.add(userDataRequest);
}
@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
HashMap < String, String > user = session.getUserDetails();
final String sessionUsername = user.get(SessionManager.KEY_USERNAME);
final String sessionPassword = user.get(SessionManager.KEY_PASSWORD);
Context mContext = getActivity().getApplicationContext();
Response.Listener < String > UpdateUserDataResponseListener = new Response.Listener < String > () {
@Override
public void onResponse(String response) {
try {
JSONObject jsonResponse = new JSONObject(response);
boolean success = jsonResponse.getBoolean("success");
if (success) {
Toast.makeText(getActivity().getApplicationContext(), "Change Successful", Toast.LENGTH_LONG).show();
} else {
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage("Konnte Nutzerdaten nicht abrufen.")
.setNegativeButton("Nochmal", null)
.create()
.show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
if (key.equals("settings_email")) {
// An mySQLDB senden
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername, sessionPassword, "email", sharedPreferences.getString(key, ""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries
prefs_email = sharedPreferences.getString(key, "");
findPreference(key).setSummary(prefs_email);
findPreference("preferencescreen_userdata").setSummary(prefs_realname + "\n" +
prefs_email + "\n" +
prefs_streetname + "\n" +
prefs_postcode + " " + prefs_city + "\n" +
prefs_state);
}
// LOTS OF SIMILAR BUTTONS FOLLOWING HERE...
}
}
因此，在重新启动用户后，错误只出现一次。 当它崩溃时，每当看起来重置时，应用程序重新启动，他可以随时更改他的任何数据。
我使用mContext变量错了吗？ 是否有一些我不清楚可能会导致崩溃的遗留值？
任何提示？ = /
答案 0 :(得分：0)
好的，我明白了。找到一些有类似问题的其他线程。
我的Context mContext = getActivity().getApplicationContext();在OnPreferenceChange方法中被调用。但这似乎很早，因为片段中的onCreate方法还没有被调用，并且我的上下文应该指向没有活动，所以这将返回null。我将 mContext 变量移动到onCreate方法，从onPreferenceChange中删除了它（进行了一些其他调整以及...），现在onPreferenceChange似乎等待onCreate方法并且它完美地工作。
package com.jamp.jamp;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.Preference;
import android.preference.PreferenceFragment;
import android.preference.PreferenceManager;
import android.support.v7.app.AlertDialog;
import android.widget.Toast;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.Volley;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.util.HashMap;
/**
* Created by Erikken on 05.09.2017.
*/
public class UserProfileSettingsFragment extends PreferenceFragment implements SharedPreferences.OnSharedPreferenceChangeListener
{
SessionManager session;
Context mContext;
String prefs_realname;
String prefs_email;
String prefs_streetname;
String prefs_postcode;
String prefs_city;
String prefs_state;
@Override
public void onCreate(final Bundle savedInstanceState)
{
final SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity().getApplicationContext());
final SharedPreferences.Editor editor = prefs.edit();
prefs.registerOnSharedPreferenceChangeListener(this);
mContext = getActivity().getApplicationContext();
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.usersettings);
session = new SessionManager(getActivity().getApplicationContext());
session.CheckLogin();
HashMap<String,String> user = session.getUserDetails();
final String sessionUsername = user.get(SessionManager.KEY_USERNAME);
final String sessionPassword = user.get(SessionManager.KEY_PASSWORD);
// ResponseListener um Request Nutzerdaten auszulesen.
Response.Listener<String> UserDataResponseListener = new Response.Listener<String>(){
@Override
public void onResponse(String response) {
try {
JSONObject jsonResponse = new JSONObject(response);
boolean success = jsonResponse.getBoolean("success");
// Wenn Datenabfrage erfolgreich, JSONResponse auswerten. // If successful, import data from mysql database
if (success) {
String responseRealName = jsonResponse.getString("realname"); if (responseRealName.equals("")) {responseRealName = getResources().getString(R.string.MissingRealName);}
String responseEmail = jsonResponse.getString("email"); if (responseEmail.equals("")) {responseEmail= getResources().getString(R.string.MissingEmail);}
String responseStreetName = jsonResponse.getString("streetname"); if (responseStreetName.equals("")) {responseStreetName = getResources().getString(R.string.MissingStreetName);}
String responsePostcode = jsonResponse.getString("postcode"); if (responsePostcode.equals("")) {responsePostcode = getResources().getString(R.string.MissingPostcode);}
String responseCity = jsonResponse.getString("city"); if (responseCity.equals("")) {responseCity = getResources().getString(R.string.MissingCity);}
String responseState = jsonResponse.getString("state"); if (responseState.equals("")) {responseState = getResources().getString(R.string.MissingState);}
int responseAge = jsonResponse.getInt ("age");
int responseIsPremium = jsonResponse.getInt ("isPremium"); // BOOLEAN
// Add data to shared prefs
editor.putString("realname",responseRealName);
editor.putString("email",responseEmail);
editor.putString("streetname",responseStreetName);
editor.putString("postcode",responsePostcode);
editor.putString("city",responseCity);
editor.putString("state",responseState);
editor.commit();
prefs_realname = prefs.getString("realname","0");
prefs_email = prefs.getString("email","0");
prefs_streetname = prefs.getString("streetname","0");
prefs_postcode = prefs.getString("postcode","0");
prefs_city = prefs.getString("city","0");
prefs_state = prefs.getString("state","0");
Preference prefUserData = (Preference) findPreference("preferencescreen_userdata");
prefUserData.setTitle(sessionUsername);
prefUserData.setSummary(prefs_realname+"\n"
+prefs_email+"\n"
+prefs_streetname+"\n"
+prefs_postcode + " " + prefs_city +"\n"
+prefs_state);
findPreference("settings_username").setTitle(sessionUsername);
findPreference("settings_realname").setSummary(prefs_realname);
findPreference("settings_email").setSummary(prefs_email);
findPreference("settings_streetname").setSummary(prefs_streetname);
findPreference("settings_postcode").setSummary(prefs_postcode);
findPreference("settings_city").setSummary(prefs_city);
findPreference("settings_state").setSummary(prefs_state);
}else{
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage("Konnte Nutzerdaten nicht abrufen.")
.setNegativeButton("Nochmal",null)
.create()
.show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
// Request an userdatarequest.php senden / Send request to userdatarequest.php
UserDataRequest userDataRequest = new UserDataRequest(sessionUsername, UserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(getActivity());
queue.add(userDataRequest);
}
@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
session = new SessionManager(mContext);
HashMap<String,String> user = session.getUserDetails();
final String sessionUsername = user.get(SessionManager.KEY_USERNAME);
final String sessionPassword = user.get(SessionManager.KEY_PASSWORD);
Response.Listener<String> UpdateUserDataResponseListener = new Response.Listener<String>(){
@Override
public void onResponse(String response) {
try {
JSONObject jsonResponse = new JSONObject(response);
boolean success = jsonResponse.getBoolean("success");
if (success){
Toast.makeText(mContext,"Change Successful",Toast.LENGTH_LONG).show();
}else{
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage("Konnte Nutzerdaten nicht abrufen.")
.setNegativeButton("Nochmal",null)
.create()
.show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
if (key.equals("settings_email")){ // Adressenprüfung mussnoch implementiert werden.
// An mySQLDB senden
//CELLNAME // CELLVALUE
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername, sessionPassword, "email", sharedPreferences.getString(key, ""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries instantly
prefs_email = sharedPreferences.getString(key, "");
findPreference(key).setSummary(prefs_email);
findPreference("preferencescreen_userdata").setSummary(prefs_realname + "\n"
+ prefs_email + "\n"
+ prefs_streetname + "\n"
+ prefs_postcode + " " + prefs_city + "\n"
+ prefs_state);
}
if (key.equals("settings_streetname")){
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername,sessionPassword,"streetname",sharedPreferences.getString(key,""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries instantly
prefs_streetname = sharedPreferences.getString(key,"");
findPreference(key).setSummary(prefs_streetname);
findPreference("preferencescreen_userdata").setSummary(prefs_realname+"\n"
+prefs_email+"\n"
+prefs_streetname+"\n"
+prefs_postcode + " " + prefs_city +"\n"
+prefs_state);
}
if (key.equals("settings_realname")){
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername,sessionPassword,"realname",sharedPreferences.getString(key,""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries instantly
prefs_realname = sharedPreferences.getString(key,"");
findPreference(key).setSummary(prefs_realname);
findPreference("preferencescreen_userdata").setSummary(prefs_realname+"\n"
+prefs_email+"\n"
+prefs_streetname+"\n"
+prefs_postcode + " " + prefs_city +"\n"
+prefs_state);
}
if (key.equals("settings_postcode")){
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername,sessionPassword,"postcode",sharedPreferences.getString(key,""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries instantly
prefs_postcode = sharedPreferences.getString(key,"");
findPreference(key).setSummary(prefs_postcode);
findPreference("preferencescreen_userdata").setSummary(prefs_realname+"\n"
+prefs_email+"\n"
+prefs_streetname+"\n"
+prefs_postcode + " " + prefs_city +"\n"
+prefs_state);
}
if (key.equals("settings_city")) {
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername,sessionPassword,"city",sharedPreferences.getString(key,""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries instantly
prefs_city = sharedPreferences.getString(key,"");
findPreference(key).setSummary(prefs_city);
findPreference("preferencescreen_userdata").setSummary(prefs_realname+"\n"
+prefs_email+"\n"
+prefs_streetname+"\n"
+prefs_postcode + " " + prefs_city +"\n"
+prefs_state);
}
if (key.equals("settings_state")) {
UpdateUserDataRequest updateUserDataRequest = new UpdateUserDataRequest(sessionUsername,sessionPassword,"state",sharedPreferences.getString(key,""), UpdateUserDataResponseListener);
RequestQueue queue = Volley.newRequestQueue(mContext);
queue.add(updateUserDataRequest);
// Summary sofort erneuern. // Refresh Summaries instantly
prefs_state = sharedPreferences.getString(key,"");
findPreference(key).setSummary(prefs_state);
findPreference("preferencescreen_userdata").setSummary(prefs_realname+"\n"
+prefs_email+"\n"
+prefs_streetname+"\n"
+prefs_postcode + " " + prefs_city +"\n"
+prefs_state);
}
}
}