Question

I am using sharedpreference to store the user name. When i did this inside my activity it is working fine. But when i pass to a common class ( which save the values ) then it fails. Could you please guide me to the place where my code need correction ?
Thanks in advance

public class Login extends Activity  implements OnClickListener{
String userId,password,userType,key="userId";  ;
EditText etName,etPassword,etUserType;
Button go; 
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.login);
    initialize();
}
private void initialize(){

    etUserType=(EditText) findViewById (R.id.etUserType);   
    etName=(EditText) findViewById (R.id.etName);
    etPassword=(EditText) findViewById (R.id.etPassword);    
    go = (Button) findViewById(R.id.bGo);
    go.setOnClickListener(this); 
}

@Override
public void onClick(View arg0) {
    // TODO Auto-generated method stub  
    userType=etUserType.getText().toString(); 
    userId=etName.getText().toString();
    password=etPassword.getText().toString();   

    if (userId.isEmpty() || password.isEmpty() ) { 
        Dialog d = new Dialog(this);
        d.setTitle("   Alert  ");
        TextView tv = new TextView(this);
        tv.setText("User Name and Password are mandatory");
        d.setContentView(tv);
        d.show();
    }else{


          StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
          StrictMode.setThreadPolicy(policy);
          try {
            List<UserType> userType = PosClient.getUserTypes();
            User user = PosClient.getUser(userId, userType.get(0)); 
            LastUser lastUser = new LastUser();
            lastUser.saveUser(key, Integer.toString(user.getUserId()));  ()); 

            if  (password.equals(user.getPassword())){ 
                Intent sendBack = new Intent();
                Bundle backpack = new Bundle();
                backpack.putString("command", "proceed");  
                backpack.putSerializable("user", user);
                sendBack.putExtras(backpack);  
                setResult(RESULT_OK, sendBack);
                finish();
            }else{
                Dialog d = new Dialog(this);
                d.setTitle("   Alert  ");
                TextView tv = new TextView(this);
                tv.setText("User Name / Password is invalid");
                d.setContentView(tv);
                d.show();
            }
          } catch (ClientProtocolException e1) { 
              e1.printStackTrace();
          } catch (IOException e1) { 
              e1.printStackTrace();
          }

    }
}



public class LastUser extends Activity{
SharedPreferences file;
public static String filename = "MySharedFile";

public  String checkUser(){  
    file = getSharedPreferences(filename,0);
    String userName = file.getString("waitername", "NOID"); 
    return userName;
} 

public void saveUser(String key,String value) {  
    filename = "MySharedFile";
    file = getSharedPreferences(filename,0);
    SharedPreferences.Editor editor = file.edit();
    editor.putString(key,value);
    editor.commit();
}

}

Error details :

12-27 12:27:41.448: E/AndroidRuntime(2983): FATAL EXCEPTION: main
12-27 12:27:41.448: E/AndroidRuntime(2983): java.lang.NullPointerException
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:153)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at com.example.restaurent.LastUser.saveUser(LastUser.java:21)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at com.example.restaurent.Login.onClick(Login.java:77)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.view.View.performClick(View.java:3534)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.view.View$PerformClick.run(View.java:14263)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.os.Handler.handleCallback(Handler.java:605)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.os.Handler.dispatchMessage(Handler.java:92)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.os.Looper.loop(Looper.java:137)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at android.app.ActivityThread.main(ActivityThread.java:4441)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at java.lang.reflect.Method.invokeNative(Native Method)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at java.lang.reflect.Method.invoke(Method.java:511)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-27 12:27:41.448: E/AndroidRuntime(2983):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

here

public class LastUser extends Activity{         //<<<<<<<<
SharedPreferences file;
public static String filename = "MySharedFile";
  // your code here
}

you are trying to Create an instance of Activity Class for Accessing methods from other Activty which is not right way. change your code as:

public class LastUser {
SharedPreferences file;
public static String filename = "MySharedFile";


public  String checkUser(Context context){  
    file = context.getSharedPreferences(filename,0);
    String userName = file.getString("waitername", "NOID"); 
    return userName;
} 

public void saveUser(String key,String value,Context context) {  
    filename = "MySharedFile";
    file = context.getSharedPreferences(filename,0);
    SharedPreferences.Editor editor = file.edit();
    editor.putString(key,value);
    editor.commit();
}

}

Now for Creating SharedPreferences from Activity just pass Activity Context to methods as :

 LastUser lastUser = new LastUser();
 lastUser.saveUser(key, Integer.toString(user.getUserId()),Login.this);