Question

I am a newbie to Android development. I have two Java files in my project. One file contains my main activity so I want to transfer the data from one Java file to another which contains the main activity.

cordovaExample.java:

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

import org.apache.cordova.*;
public class cordovaExample extends DroidGap
{
@Override
 public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    super.loadUrl("file:///android_asset/www/index.html");

    Bundle extras = getIntent().getExtras();
    String phno = extras.getString("novel.PhoneNumber");
   Toast.makeText(getApplicationContext(),phno,Toast.LENGTH_LONG).show();



}
}

novel.java

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

public class novel extends Activity
{ 
public String PhoneNumber;
Context mcontext;
public String getNumber()
{



 TelephonyManager tMgr=(TelephonyManager)mcontext.getSystemService(Context.TELEPHONY_SERVICE); 

         Intent intent = new Intent(this, cordovaExample.class);
            intent.putExtra("novel.PhoneNumber", PhoneNumber);
                startActivity(intent);
               return PhoneNumber = tMgr.getLine1Number();
        }

}

So i want to transfer the "PhoneNumber" from novel.java to cordovaExample.java but in novel.java, After running the application i am getting "unfortunately app has stopped" in emulator.

this is the logcat

08-12 15:49:37.657: E/AndroidRuntime(779): FATAL EXCEPTION: main
08-12 15:49:37.657: E/AndroidRuntime(779): java.lang.RuntimeException: Unable to start activity  ComponentInfo{org.apache.cordova.example/org.apache.cordova.example.cordovaExample}: java.lang.NullPointerException
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.access$600(ActivityThread.java:123)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.os.Looper.loop(Looper.java:137)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.main(ActivityThread.java:4424)
08-12 15:49:37.657: E/AndroidRuntime(779):  at java.lang.reflect.Method.invokeNative(Native Method)
08-12 15:49:37.657: E/AndroidRuntime(779):  at java.lang.reflect.Method.invoke(Method.java:511)
08-12 15:49:37.657: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-12 15:49:37.657: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-12 15:49:37.657: E/AndroidRuntime(779):  at dalvik.system.NativeStart.main(Native Method)
08-12 15:49:37.657: E/AndroidRuntime(779): Caused by: java.lang.NullPointerException
08-12 15:49:37.657: E/AndroidRuntime(779):  at org.apache.cordova.example.cordovaExample.onCreate(cordovaExample.java:20)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.Activity.performCreate(Activity.java:4465)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
08-12 15:49:37.657: E/AndroidRuntime(779):  ... 11 more

Also, if I try the simple program I get the same result:

cordovaExample.java

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

import org.apache.cordova.*;
public class cordovaExample extends DroidGap
{
@Override
 public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    super.loadUrl("file:///android_asset/www/index.html");

   novel c=new novel()
   int a=c.getNumber();
   Toast.makeText(getApplicationContext(),a,Toast.LENGTH_LONG).show();



}
}

novel.java

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

public class novel extends Activity
{ 
public int a=0;
public int getNumber()
{

    a=5;

 return a;
        }

}

How can I resolve this?

Answer 1

Android API guide contains a definitive FAQ item about how to pass data between between Activities/Services within a single application.

try this,

do like this in novel to set the phone number

Intent myIntent = new Intent(novel.this, cordovaExample.class);
myIntent.putExtra("phone", 989898989);
startActivity(myIntent);

in cordovaExample file do following to get the phoneNumber

Bundle b = this.getIntent().getExtras();
String i = b.getString("phone");

if you are not able to pass the data then alternative way is to declare public method and pass them, see following example,

novel.java

private static String phoneNumber = "";

public void onCreate()
{
    ...
    phoneNumber = "9898989898";
    ...
}

public static String getPhoneNumber()
{
      return phoneNumber;
}

cordovaExample.java

private static String phoneNumber = ""; 

phoneNumber = novel.getPhoneNumber();