I'm working on having a "Keep me on Logged in" state on my app. How should i do it?

Here's my xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="horizontal"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:background="#FFFFFF">

    <TextView android:id="@+id/welcome_text"
        android:text = "Log-In"   
        android:textColor="#000000"        
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="40dp"
        android:layout_centerHorizontal="true"/>
     <TextView
        android:id="@+id/username_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_marginRight="20dip"
        android:layout_marginTop="100dip"
        android:layout_marginLeft="30dip"
        android:text="Username:"
        android:textColor="#000000"/>
    <EditText
        android:id="@+id/txt_username"
        android:layout_width="150dip"
        android:layout_height="wrap_content"
        android:background="@android:drawable/editbox_background"
        android:layout_toRightOf="@id/username_text"
        android:layout_alignTop="@id/username_text"/>
     <TextView
        android:id="@+id/password_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@id/username_text"
        android:layout_marginRight="20dip"
        android:layout_marginTop="30dip"
        android:layout_marginLeft="30dip"
        android:text="Password:"
        android:textColor="#000000"/>
    <EditText
        android:id="@+id/txt_password"
        android:layout_width="150dip"
        android:layout_height="wrap_content"
        android:background="@android:drawable/editbox_background"
        android:layout_toRightOf="@id/password_text"
        android:layout_alignTop="@id/password_text"
        android:layout_below="@id/txt_username"
        android:layout_marginLeft="5dip"
        android:password="true"        />
    <Button
        android:id="@+id/login_button"
        android:layout_width="100dip"
        android:layout_height="wrap_content"
        android:layout_below="@+id/txt_password"
        android:layout_alignParentLeft="true"
        android:layout_marginTop="35dip"
        android:layout_marginLeft="110dip"
        android:text="Submit" />
     <TextView
        android:id="@+id/tv_error"
        android:layout_width="开发者_如何学Gofill_parent"
        android:layout_height="40dip"
        android:textSize="5pt"
        android:layout_alignParentLeft="true"
        android:layout_below="@id/txt_password"
        android:layout_marginRight="9dip"
        android:layout_marginTop="9dip"
        android:layout_marginLeft="15dip"
        android:textColor="#FF0000"
        android:text=""/>
     <TextView android:id="@+id/tv_login"
        android:text = "@string/Login"   
        android:textColor="#000000"        
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="40dp"
        android:layout_below="@id/login_button"
        android:layout_centerHorizontal="true"/>
     <RadioGroup
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/tv_login"
      android:orientation="horizontal"
      android:layout_centerHorizontal="true">
      <RadioButton android:id="@+id/on"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="9dip"
          android:text="On" 
          android:textColor="#000000"/>
      <RadioButton android:id="@+id/off"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_marginTop="9dip"
          android:layout_marginLeft="20dip"
          android:text="Off" 
          android:textColor="#000000"/>
    </RadioGroup>
</RelativeLayout>

and here's my java:

public class LogInActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.loginactivity);

        final RadioButton radio_on = (RadioButton) findViewById(R.id.on);
        final RadioButton radio_off = (RadioButton) findViewById(R.id.off);

        Button launch = (Button)findViewById(R.id.login_button);
        launch.setOnClickListener(new OnClickListener()
        {
         public void onClick(View v) {
           EditText usernameEditText = (EditText) findViewById(R.id.txt_username);
           EditText passwordEditText = (EditText) findViewById(R.id.txt_password);
           TextView loginTextView = (TextView)findViewById(R.id.tv_error);

           String sUserName = usernameEditText.getText().toString();
           String sPassword = passwordEditText.getText().toString();

            if(sUserName.equals("numlock") && sPassword.equals("numlock")) {
                Intent intent = new Intent(LogInActivity.this, HomeActivity.class);
                startActivity(intent);
            }
             else {
                loginTextView.setText("Login failed. Username and/or password doesn't match.");
                 }
            }
        }); 
    }
}

I want to assign the keep me logged in state on the radio buttons. Any help?

you should save the login credentials in sharedPreferences or Sqlite and on login activity check if you find any saved data then login with the saved data else ask user for credentials..

You can do it by using SharedPreference, Static variables or by Application class which will helps you in keeping the state of the User