编译我的代码时，我收到此错误
java.lang.NullPointerException: Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences.edit()'
我仍然无法理解为什么。对于这些错误我的应用程序崩溃。请帮助我，我无法找到我所犯的确切错误。
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences.edit()' on a null object reference
at com.chatbook.loki.chatbook.SessionManger.<init>(SessionManger.java:16)
at com.chatbook.loki.chatbook.Login.onCreate(Login.java:44)
at android.app.Activity.performCreate(Activity.java:6001)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2368)
Here is my code
SessionManager.java
public class SessionManger {
SharedPreferences pref;
SharedPreferences.Editor editor = pref.edit();
Context _context;
int PRIVATE_MODE = 0;
private static final String PREF_NAME = "exmaple";
private static final String IS_LOGIN = "IsLoggedIn";
public static final String KEY_EMAIL = "email";
public static final String KEY_PASSWORD = "password";
public SessionManger(Context context){
this._context = context;
pref = _context.getSharedPreferences(PREF_NAME,PRIVATE_MODE);
editor = pref.edit();
editor.apply();
}
public void createLoginSession(String email, String password){
editor.putBoolean(IS_LOGIN,true);
editor.putString(KEY_EMAIL, email);
editor.putString(KEY_PASSWORD, password);
editor.commit();
}
public boolean isLoggedIn(){
return pref.getBoolean(IS_LOGIN,true);
}
public void checkLogin(){
if(!this.isLoggedIn()){
Intent in = new Intent(_context,Login.class);
in.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
in.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
_context.startActivity(in);
}
}
public HashMap<String, String> getUserDetails(){
HashMap<String,String> user = new HashMap<String, String>();
user.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null));
user.put(KEY_PASSWORD, pref.getString(KEY_PASSWORD, null));
return user;
}
public void logout(){
editor.clear();
editor.commit();
Intent in = new Intent(_context,Login.class);
in.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
in.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
_context.startActivity(in);
}
}
和我的登录活动文件
public class Login extends AppCompatActivity {
Button b1,b2,b3;
EditText e1,e2;
FirebaseAuth auth;
ProgressBar pgbar;
SessionManger session;
Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
auth = FirebaseAuth.getInstance();
b1 = (Button) findViewById(R.id.logBsign);
b2 = (Button) findViewById(R.id.logBlog);
b3 = (Button) findViewById(R.id.logBreset);
e1 = (EditText) findViewById(R.id.logeditemail);
e2 = (EditText) findViewById(R.id.logeditpass);
pgbar = (ProgressBar) findViewById(R.id.progressBar);
session = new SessionManger(context.getApplicationContext());
}
public void signup(View v) {
Intent in = new Intent(Login.this, SignUp.class);
startActivity(in);
}
public void login(View v){
/*Intent in = new Intent(Login.this, MainActivity.class);
startActivity(in);*/
final String email = e1.getText().toString().trim();
final String password = e2.getText().toString().trim();
if(TextUtils.isEmpty(email)){
Toast.makeText(getApplicationContext(),"Enter email address", Toast.LENGTH_SHORT).show();
return;
}
if(TextUtils.isEmpty(password)){
Toast.makeText(getApplicationContext(), "Enter password", Toast.LENGTH_SHORT).show();
return;
}
pgbar.setVisibility(View.VISIBLE);
auth.signInWithEmailAndPassword(email,password).addOnCompleteListener(Login.this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
pgbar.setVisibility(View.GONE);
if(!task.isSuccessful()){
if(password.length() < 6){
e1.setError(getString(R.string.minimum_password));
}else{
Toast.makeText(Login.this, getString(R.string.auth_failed),Toast.LENGTH_SHORT).show();
}
}else{
session.createLoginSession(email, password);
Intent in = new Intent(Login.this, MainActivity.class);
startActivity(in);
//finish();
}
}
});
}
public void reset(View v){
Intent in = new Intent(Login.this, ResetPassword.class);
startActivity(in);
}
//To exit from App
public boolean exit = false;
@Override
public void onBackPressed() {
if(exit){
finish();;
}
else{
Toast.makeText(this,"Press again to exit",Toast.LENGTH_SHORT).show();
exit = true;
}
}
}
答案 0 :(得分：1)
不要
session = new SessionManger(context.getApplicationContext());
<强>不要
session = new SessionManger(Login.this);
和
SharedPreferences pref;
Editor editor;
Context _context;
int PRIVATE_MODE = 0;
然后
// Constructor
public SessionManager(Context context){
this._context = context;
pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
editor = pref.edit();
}
答案 1 :(得分：0)
可以像下面一样编辑共享首选项，传递正确的名称
SharedPreferences sharedPreferences = PreferenceManager
.getDefaultSharedPreferences(this);
Editor editor = sharedPreferences.edit();
editor.putString(key, name);
editor.apply();
SharedPreferences sharedPreferences = PreferenceManager
.getDefaultSharedPreferences(this);
String name = sharedPreferences.getString(key, "default value");
答案 2 :(得分：0)
修复全局变量cause null
SharedPreferences.Editor editor = pref.edit(); <-- wrong pref cause null
SharedPreferences.Editor editor; <-- just this
可选
@SuppressLint("CommitPrefEdits")
public SessionManger(Context context){
this._context = context;
pref = _context.getSharedPreferences(PREF_NAME,PRIVATE_MODE);
editor = pref.edit();
//editor.apply(); //no need for apply
}
答案 3 :(得分：0)
这是因为你的pref是null ... SharedPreferences pref = getApplicationContext（）。getSharedPreferences（“MyPref”，MODE_PRIVATE）;
答案 4 :(得分：0)
SharedPreferences pref;
SharedPreferences.Editor editor = pref.edit();
pref为null;