Question

I want to use the value of a string variable in one class into another…

But when i do so by creating an object in the calling class of the called class, i get the value as null.

I tried searching on the net and stack overflow and went through some similar answers,but the solutions to them were specific to those questions.So m asking again.

here are the 2 classes –

1st one is the class from which i want to use the variable.
class is – SelectedClass variable i want to use in another class – SelectedClass( a string)

2nd class is FEa.I want to use the value of the variable “SelectedClass” from the 1st class.

CLASS 1(SelectedClass)-

package com.attendance_trial.nirmik;

import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class SelectClass extends ListActivity 
{

public String classes2[] = {"FEa","FEb","SEa","SEb"};
String SelectedClass;

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
    // TODO Auto-generated method stub
    super.onListItemClick(l, v, position, id);

    String SelectedClass = classes2[position];
    try
    {

        Class MyClass = Class.forName("com.attendance_trial.nirmik." + SelectedClass);
        Intent myintent = new Intent(SelectClass.this,MyClass);
        startActivity(myintent);

    }
    catch(ClassNotFoundException cnf)
    {
        cnf.printStackTrace();
    }


}

@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    // TODO Auto-generated method stub
    setListAdapter(new ArrayAdapter<String>(SelectClass.this, android.R.layout.simple_list_item_1, classes2));
}   

}

CLASS 2 (FEa) –

package com.attendance_trial.nirmik;



import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class FEa extends Activity implements View.OnClickListener
{

SelectClass sc = new SelectClass();

//Button b1,b2,b3,b4,b5,b6,b7,b8,b9,b10,b11,b12,bSend;
Button bSend;
TextView tvDisp;
String acc="";


@Override
protected void onCreate(Bundle savedInstanceState)
{
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fea);
    initialise();


}



private void initialise()//initialise all buttons etc
{

    bSend = (Button) findViewById (R.id.BtnSendMsg);
    bSend.setOnClickListener(this);
    tvDisp=(TextView) findViewById (R.id.TxtViewDisplay);

}





public void onButtonClick(View v)
{
    // TODO Auto-generated method stub


        Button theButton = (Button)v;
        String chk = theButton.getText().toString();
        if(chk.contentEquals("1")||chk.contentEquals("2")||chk.contentEquals("3")||chk.contentEquals("4")||chk.contentEquals("5")
                ||chk.contentEquals("6")||chk.contentEquals("7")||chk.contentEquals("8")||chk.contentEquals("9"))
        {
        acc = acc + "0" + chk;
        }
        else
        {
            acc =  acc +chk;
        }
        tvDisp.setText("String Is:" + acc);


}//method end



@Override
public void onClick(View v2) 
{
    // TODO Auto-generated method stub
    int retid = v2.getId();
    if(retid == R.id.BtnSendMsg ) //send button clicked
    {

        String msg = sc.SelectedClass + "2210"+ acc;
                Intent emailIntent = new Intent(android.content.Intent.ACTION_SEND);
                emailIntent.setType("plain/text");
                emailIntent.putExtra(android.content.Intent.EXTRA_TEXT, msg);
                startActivity(emailIntent);
    }

}

}//main end

Answer 1

What you are doing is totally wrong.

You are not supposed to manually create objects from a class which extends an Activity. AKA you should never do this: SelectClass sc = new SelectClass();.
You have to tell the Android OS to do it for you by using:

Intent intent = new Intent(this, YourActivity.class);
startActivity(intent);

Now if you want to send a String from SelectClass to FEa, you can send it with the intent like this:

Intent intent = new Intent(this, YourActivity.class);
intent.putExtra(EXTRA_MESSAGE_KEY, yourString);
startActivity(intent);

And in your second Activity, in onCreate():

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Get the string from the intent
    Intent intent = getIntent();
    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

}

You should check developer.android.com to make yourself an idea how to program in Android. Bare in mind, Android programming is not Java programming.

How to start a new Activity, from the developers site here.