SharedPreferences类

Question

I'm creating an app which ask the first time user to input a password. However whenever I press the Submit button the application stops and I think it's because of the class I made for he SharedPreferences. I don't know what to put in the class. Need some help please. Thanks

package com.android.steg;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class Password extends Activity implements OnClickListener
{
Button submitButton;
EditText passwordEditText;
private SharedPreferences SharedPreference;
public static final String PREFS_PRIVATE = "PREFS_PRIVATE";
public static final String KEY_PRIVATE = "KEY_PRIVATE";
public static final String PREFS_READ = "PREFS_READ";
public static final String KEY_READ = "KEY_READ";
public static final String PREFS_WRITE = "PREFS_WRITE";
public static final String KEY_WRITE = "KEY_WRITE";
public static final String PREFS_READ_WRITE = "PREFS_READ_WRITE";
public static final String KEY_READ_WRITE = "KEY_READ_WRITE";



public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.pass);
    Button submitButton = (Button) findViewById(R.id.submitButton);
    submitButton.setOnClickListener(this);
}

public void onClick(View v)
{ 
    EditText passwordEditText = (EditText) findViewById(R.id.passwordEditText);
    SharedPreferences prefs = this.getApplicationContext().getSharedPreferences("prefs_file",MODE_PRIVATE);
    String password = prefs.getString("password","");
    if(password=="")
    {
        Editor edit = prefs.edit();
        edit.putString("password",passwordEditText.getText().toString());
        edit.commit();
        StartMain();
    }
    else
    {
        if(passwordEditText.getText().toString()== password)
        {
             StartMain();
        }
    }

}

public void StartMain()
{
     Intent intent = new Intent(this, MainActivity.class);
     startActivity(intent);
}
 }

Whenever I press the submit button, it won't send me to the start the MainActivity class.

Answer 1

You are not comparing Strings correctly. Replace

if(password=="")

with

if("".equals(password))

and

if(passwordEditText.getText().toString()== password)

with

if(passwordEditText.getText().toString().equals(password))

EDIT
The reason you need to make these changes is that (password=="") will always be false , so the else block will always execute. Within the else block, the only test is (passwordEditText.getText().toString()== password) and this will also always be false . As such, the two calls to StartMain() are both within unreachable code blocks and are never executed. You can easily demonstrate this by putting a bunch of Log.d("MY_TAG","message goes here"); lines in the various if and else blocks.

EDIT 2
Ah. Woops. There is an additional issue with the code that I was blinded to by the obviousness of the String comparison issue. You are confusing the scope of your button declaration. You first define it for the class:

Button submitButton;

The you redefine it within onCreate() :

Button submitButton = (Button) findViewById(R.id.submitButton);

Change this last line to:

submitButton = (Button) findViewById(R.id.submitButton);