CODEWITHSUNDEEP
javaandroideclipsejar
Anand K
Anand K

Reputation: 233

How to call a method from android library class

I want to call a method from a android library class which i have imported as a androidlib.jar. As i am able to call a whole class of library but i dont want it, but i want to call a particular method of library class.

I tried something like this, but it is showing java.lang.Nullpointer exception

This is my library class (AndroidLiB.class), where i have imported its jar file

  public class AndroidLiB extends Activity  {

   @Override
   protected void onCreate(Bundle savedInstanceState) 
    {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.android_li_b);
    startGPS();
    }

    public void startGPS()
    {
     Toast.makeText(getApplicationContext(),"Your GPS started",Toast.LENGTH_LONG).show();
    }

}

This is my application class where i want to call a method from above class

  public class AndLib1 extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.and_lib1);
    AndroidLiB abc = new AndroidLiB();
    abc.startGPS();

    }

}

But it is not working

Upvotes: 0

Views: 2316

Answers (4)

Prakash M
Prakash M

Reputation: 651

If you want simply a method from jar, then why you need to extends Activity. My suggestion is remove extends Activity will fix the NPE error.

Try this,

 public class AndroidLiB {
  Activity activity;
  AndroidLiB(Activity activity){ 
        this.activity = activity;
   }


  public void startGPS()
  {
    Toast.makeText(activity,"Your GPS started",Toast.LENGTH_LONG).show();
  }

 }

And In your main class call like

 AndroidLiB lib = new AndroidLiB (this);
 lib.startGPS();

Upvotes: 1

kstachniuk
kstachniuk

Reputation: 358

You can extend library class. For example:

public class YourActivity extends AndroidLib
{
  super.onCreate(savedInstanceState);
  setContentView(R.layout.and_lib1);
  startGPS();
}

Upvotes: 1

user180100
user180100

Reputation:

I would do something like this:

public class Tool {
    private Tool() {
        // no direct instantiation
    }    

    public static void startGPS(final Context context) {
         Toast.makeText(context, "Your GPS started", Toast.LENGTH_LONG).show();
    }
}

then

public class AndroidLiB extends Activity  {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.android_li_b);
        Tool.startGPS(this);
    }
}

and

public class AndLib1 extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.and_lib1);
        Tool.startGPS(this);
    }
}

Upvotes: 1

Tamby Kojak
Tamby Kojak

Reputation: 2159

What you're trying to do isn't really the best way to do things, but I'm assuming that the question being asked is how to import the jar correctly. If so:

If using eclipse,

  1. Make sure the androidlib.jar file is in the libs folder.
  2. Right click on androidlib.jar and select Build Path > Add to Build Path
  3. Right click on your project folder, go to Properties > Java Build Path > Order and Export and then make sure androidlib.jar is selected.

The problem with your current code is that when you call getApplicationContext(), the Activity hasn't been started yet, therefore there is no context. A quick and dirty solution would be to rewrite the startGPS() method like this:

public static void startGps(Context context, String message) {
    Toast.makeText(context, message, Toast.LENGTH_LONG).show();
}

But I would much rather put that method inside some sort of Utilities class or even inside a parent Activity class.

Upvotes: 0

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