保存凭据sharedpreferences

Question

我想保存用户凭据使用sharedpreferences，我通过这种方式这样做，但它不工作

public class MainActivity extends Activity { 
    public EditText UserName; 
    public EditText Password; 
    public Button mButton; 
    public String user_name; 
    public String pass_word; 
    public CheckBox mCheckSavePassword; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     UserName = (EditText) findViewById(R.id.textUserName); 
     Password = (EditText) findViewById(R.id.textPassword); 
     mButton = (Button) findViewById(R.id.buttonLogin); 
     mCheckSavePassword = (CheckBox) findViewById(R.id.checkSavePassword); 

     mCheckSavePassword = (CheckBox) findViewById(R.id.checkSavePassword); 
     SharedPreferences.Editor preferencesEditor = preferences.edit();      
     preferencesEditor.putString("prefUserName", user_name);     
     if(mCheckSavePassword.isChecked()) { 
      preferencesEditor.putString("prefPassword", pass_word); 
     }     
     preferencesEditor.putBoolean("prefSavePassword", mCheckSavePassword.isChecked()); 
     preferencesEditor.apply(); 
    } 

Answer 1

要保存空值，当第一次创建活动，user_name和pass_word尚未初始化。

onCreate是你应该阅读这些偏好值和更新这些值EditTexts。应该通过某些用户交互来完成保存，例如按下按钮时。