如何使用Android中的sharedpreferences更改PIN码？

Question

我在实现机器人演示使用，我输入PIN码并确认口来问题共享偏好申请销的是，当我访问这个值，它没有返回更新后的值，它给了我NullPointerException。

String strGetPin; 
public final String pref_filename = "settings"; 
String myPassword; 
static SharedPreferences shaedPref; 
public static String strdataReturned = ""; 

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.settings_list); 
    activity = this; 
    edtxt_EnterPin = (EditText) findViewById(R.id.edtxt_Pin); 
    edtxt_NewPin = (EditText) findViewById(R.id.edtxt_NewPin); 
    edtxt_ConfirmPin = (EditText) findViewById(R.id.edtxt_ConfirmPin); 
    shaedPref = getSharedPreferences(pref_filename, 0); 
    strdataReturned = shaedPref.getString("user", ""); 
    if (strdataReturned.equals("")) { 
    SharedPreferences.Editor editor = shaedPref.edit(); 
    editor.putString("user", "1234"); // newData is new pass,passwordKey is key 
    editor.commit(); 
    } 
    btnChangePin = (Button) findViewById(R.id.btn_ChangePin); 

    btnChangePin.setOnClickListener(new OnClickListener() { 
    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 
     myDialog = new Dialog(Settings_Activity.this); 
     myDialog.setContentView(R.layout.pin_change); 
     myDialog.setTitle("Application PIN Change"); 
     myDialog.setCancelable(false); 
     //Button For Change Pin save 
     Button btnChange = (Button) myDialog.findViewById(R.id.btn_Save); 

     btnChange.setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View arg0) { 
      // TODO Auto-generated method stub 
      String stringData = edtxt_EnterPin.getText().toString().trim(); 
      strdataReturned = shaedPref.getString("user", ""); // key/def message 
      // if stored password is equal to entered password 
      if (strdataReturned.equals(stringData)) { 
      String newData = edtxt_NewPin.getText().toString().trim(); 
      SharedPreferences.Editor editor = shaedPref.edit(); 
      editor.putString("user", newData); // newData is new pass, passwordKey is key 
      editor.commit(); 
      Toast.makeText(getApplicationContext(), "PIN Change successfully", Toast.LENGTH_LONG).show(); 
      edtxt_EnterPin.setText(""); 
      edtxt_NewPin.setText(""); 
      } else { 
      Toast.makeText(getApplicationContext(), "Wrong Pin!", Toast.LENGTH_LONG).show(); 
      edtxt_EnterPin.setText(""); 
      edtxt_NewPin.setText(""); 
      } 
     } 
     }); 
     Button btnCancel = (Button) myDialog.findViewById(R.id.btn_Cancel); 

     btnCancel.setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      // TODO Auto-generated method stub 
      myDialog.dismiss(); 
     } 
     }); 
     myDialog.show(); 
    } 
    }); 
} 

的logcat：

04-09 18:42:12.694: D/(29235): onClick: Stoping Service 
04-09 18:42:12.781: E/(29235): Service Stopped 
04-09 18:42:19.861: D/dalvikvm(29235): GREF has increased to 201 
04-09 18:42:50.712: D/AndroidRuntime(29235): Shutting down VM 
04-09 18:42:50.712: W/dalvikvm(29235): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
04-09 18:42:50.721: E/AndroidRuntime(29235): FATAL EXCEPTION: main 
04-09 18:42:50.721: E/AndroidRuntime(29235): java.lang.NullPointerException 
04-09 18:42:50.721: E/AndroidRuntime(29235): at com.sms_alert.Settings_Activity$1$1.onClick(Settings_Activity.java:95) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at android.view.View.performClick(View.java:2485) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at android.view.View$PerformClick.run(View.java:9080) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at android.os.Handler.handleCallback(Handler.java:587) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at android.os.Handler.dispatchMessage(Handler.java:92) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at android.os.Looper.loop(Looper.java:123) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at android.app.ActivityThread.main(ActivityThread.java:3683) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at java.lang.reflect.Method.invokeNative(Native Method) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at java.lang.reflect.Method.invoke(Method.java:507) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
04-09 18:42:50.721: E/AndroidRuntime(29235): at dalvik.system.NativeStart.main(Native Method) 
04-09 18:42:53.932: I/Process(29235): Sending signal. PID: 29235 SIG: 9 

Answer 1

尝试写入之前清除SharedPreferences。

editor.clear();