SharedPreferences在Android应用程序记住我按钮

林不知道我在做什么错。在我的应用程序中，我试图让它记住提交时输入到文本框中的以前的密码。从使用共享首选项进行的研究保存变量，即使应用程序重新启动。顶我的代码：SharedPreferences在Android应用程序记住我按钮

public class AK_Voucher_access extends BT_fragment{ 

View thisScreensView = null; 

String errormessage = ""; 
String errormessageTextColor = ""; 
String errormessageText = ""; 
String rememberTextText = ""; 
String rememberTextTextColor = ""; 
String voucherTextfieldPlaceholder = ""; 
String voucherTextfieldSecureTextEntry = ""; 
boolean voucherTextfieldSecureTextEntryBool = false; 
String iphoneImage = ""; 
String ipadImage = ""; 
String errormessageInvalid = ""; 
String errormessageRemember = ""; 

private TextView errormessageTextView = null; 
private EditText voucherTextfieldEditText = null; 
private ImageView imageView = null; 
private Button submitButton = null; 
private Switch rememberSwitch = null; 

private Drawable myHeaderImageDrawable = null; 
private String alphaImage = "", pass; 
private static BT_item screenObjectToLoad = null; 
private static final String PASSVALUE = "value"; 
//private static final String appPassword = "appPassword"; 
Context context;

要检索文本框时设定：

if (rememberSwitch.isChecked()) { 
      BT_debugger.showIt(fragmentName + ":rememberSwitch is ON"); 

     SharedPreferences settings = context.getSharedPreferences(PASSVALUE, MODE_PRIVATE); 

     String rpass= settings.getString("rpassword",""); 


      if (rpass!=null) { 
        voucherTextfieldEditText.setText(rpass); 
      } else { 
       voucherTextfieldEditText.setText("nono"); 
      } 

    } 
    else { 
     BT_debugger.showIt(fragmentName + ":rememberSwitch is OFF"); 
     // switchStatus.setText("Switch is currently OFF"); 
    }

然后我的代码，以节省提交的字符串：

if (loadScreenNickname.length() > 1 && !loadScreenNickname.equalsIgnoreCase("none")) { 

       // before we launch the next screen... 
       if (!rememberSwitch.isChecked()) { 
        voucherTextfieldEditText.setText(""); 
       } 

       if (rememberSwitch.isChecked()){ 
        //voucherTextfieldEditText.setText(""); 

        String pass = voucherTextfieldEditText.getText().toString(); 
        BT_debugger.showIt(pass + ":CODE"); 

        SharedPreferences settings = context.getSharedPreferences(PASSVALUE, MODE_PRIVATE); 
        settings.edit().putString("rpassword", pass).apply(); 

        rememberSwitch.setChecked(true); 



       } 
       errormessageTextView.setVisibility(View.GONE); 
       errormessageTextView.invalidate(); 

       //loadScreenObject(null, thisScreen); 
       try { 
        loadScreenWithNickname(loadScreenNickname); 

        foundIt = 1; 

       } catch (Exception ex){ 
        Log.e ("eTutorPrism Error", "Caught this exception " + ex); 
        ex.printStackTrace(); 
       } 
       break; 
      } 
     }

但是加班我运行中的插件我应用程序我在logcat中收到此错误：

E/UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference 
                   at com.asfapp.ui.bt_plugins.AK_Voucher_access.onCreateView(AK_Voucher_access.java:210) 


E/AndroidRuntime: FATAL EXCEPTION: main 
                 Process: com.asfapp, PID: 24771 
                 java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference 
                  at com.asfapp.ui.bt_plugins.AK_Voucher_access.onCreateView(AK_Voucher_access.java:210)

不知道这次代码有什么问题，但任何事情都应该有所帮助。

来源

2017-09-13 TheSwindler44

使用该代码来获得SharedPreference在fragment

SharedPreferences preferences = this.getActivity().getSharedPreferences("myPref", Context.MODE_PRIVATE);

来源

2017-09-13 17:15:16

尝试

Context context = getApplicationContext(); 
SharedPreferences settings = context.getSharedPreferences(PASSVALUE, context.MODE_PRIVATE);

你得到NullPointerException异常，因为环境是不确定的。在调用context.getSharedPreference（）之前定义它，或者使用其他方式，如getApplicationContext（）。getSharedPreference（）。

来源

2017-09-13 16:42:33

您是否定义了上下文？

Context context;

我没有在这里看到上下文的值。也许这就是为什么它返回的原因NullPointerException 你应该用活动或上下文来定义它。你也可以做到这一点，而不是让背景VAR： getApplicationContext().getSharedPreferences() 或者 getActivity().getSharedPreferences()

来源

2017-09-13 16:42:33

SharedPreferences在Android应用程序记住我按钮

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