android - 共享首选项返回空值

android - sharedpreferences return null value

提问by chinna_82

I'm trying to use sharedpreferences to check whether the user logged in before they start using the app. I save the username in shredpreferences when user log in.

我正在尝试使用 sharedpreferences 来检查用户是否在开始使用应用程序之前登录。当用户登录时，我将用户名保存在 shredpreferences 中。

Login.java

登录.java

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);     
        Button btnLogin = (Button) findViewById(R.id.buttonlogin);      
        btnLogin.setOnClickListener(new View.OnClickListener() {
            public void onClick(View adapt) {
                EditText usernameEditText = (EditText) findViewById(R.id.EditUserName);
                userName = usernameEditText.getText().toString();
                EditText passwordEditText = (EditText) findViewById(R.id.EditPassword);
                userPassword = passwordEditText.getText().toString();               
                if (userName.matches("") && userPassword.matches("")) {
                    toast("Please enter Username and Password");
                    return;
                } else if (userName.matches("") || userName.equals("")) {
                    toast("Please enter Username");
                    return;
                } else if (userPassword.matches("") || userPassword.equals("")) {
                    toast("Please enter Password");
                    return;
                } else {
                    SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
                    SharedPreferences.Editor editor = sharedPreferences.edit();
                    editor.putString("MEM1", userName);
                    editor.commit();
                    new DownloadFilesTask().execute();
                }           
            }
        });
    }

    private void toast(String text) {
        Toast.makeText(this, text, Toast.LENGTH_SHORT).show();
    }

    private class DownloadFilesTask extends AsyncTask<Void, Void, Void> {
        protected void onPreExecute() {
        }

        protected void onPostExecute(Void result) {
            toast("user logged in");
            startActivity(new Intent(Login.this, MainActivity.class));
            finish();
        }

        @Override
        protected Void doInBackground(Void... params) {         
            return null;
        }
    }

}

and I tried to check the username value before I start my mainactivity.

在开始我的主要活动之前，我尝试检查用户名值。

SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
    String username =sharedPreferences.getString("MEM1", "");
    if(username.equalsIgnoreCase("")||username.length()==0)
    {
        toast("username is null");
        startActivity(new Intent(MainActivity.this, Login.class));
        finish();
    }

but the username is always null. Please help. Thanks

但用户名始终为空。请帮忙。谢谢

回答by Zyber

Calling getPreferencesmeans that you have to be in the same activity. Using getSharedPreferencesallows you to share the preferences between activities. You just have to define a name for the preferences when calling getSharedPreferences("Pref name here", MODE_PRIVATE);

打电话getPreferences意味着你必须在同一个活动中。使用getSharedPreferences允许您在活动之间共享首选项。您只需要在调用时为首选项定义一个名称getSharedPreferences("Pref name here", MODE_PRIVATE);

回答by Dipak Keshariya

Write below Code instead of your code to save username into sharedpreferences.

在下面写代码而不是你的代码来将用户名保存到共享首选项中。

SharedPreferences myPrefs = this.getSharedPreferences("myPrefs", MODE_WORLD_READABLE);
SharedPreferences.Editor editor = myPrefs.edit();
editor.putString("MEM1", userName);
editor.commit();

And Use below code For Get Preferences Value.

并使用以下代码获取首选项值。

SharedPreferences myPrefs = this.getSharedPreferences("myPrefs", MODE_WORLD_READABLE);
String username = myPrefs.getString("MEM1","");

回答by Nicu P

private final String TAXI_SPREF = "TAXI_SHARED_PREFERENCES";

//set-save data to shared preferences
SharedPreferences.Editor sPEditor = getSharedPreferences(TAXI_SPREF, MODE_PRIVATE).edit();
sPEditor.putInt("USERID", etUserID.getText().toString());
sPEditor.putString("EMAIL", etEmail.getText().toString());
sPEditor.apply();

//get data from shared preferences

SharedPreferences sharedPreferences = getSharedPreferences(TAXI_SPREF, MODE_PRIVATE);
int userID = sharedPreferences.getInt("USERID", 0);
string email = sharedPreferences.getString("EMAIL", 0);
////////     or         /////
String email = getSharedPreferences(TAXI_SPREF, MODE_PRIVATE).getString("EMAIL","EMPTY");
    if (!email.equals("EMPTY")){
        etEmail.setText(email);
    }