共享的首选项返回空值 [英] android - sharedpreferences return null value

问题描述

我正在尝试使用sharedpreferences来检查用户在开始使用该应用程序之前是否已登录.用户登录时，我将用户名保存在shredpreferences中.

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.

Login.java

Login.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;
        }
    }

}

，并且在开始进行mainactivity之前，我尝试检查用户名值.

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

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();
    }

，但用户名始终为null.请帮忙.谢谢

but the username is always null. Please help. Thanks

推荐答案

在下面的代码(而不是您的代码)中编写代码，以将用户名保存到共享首选项中.

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

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

并使用以下代码获取首选项值.

And Use below code For Get Preferences Value.

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

这篇关于共享的首选项返回空值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！