Launch Facebook from your application

First of all you are required to check if Facebook exists in your mobile device or not. To do so create a method like below

@SuppressWarnings("unused")

private boolean isFacebookExists() {

    try{

        ApplicationInfo info = getPackageManager().getApplicationInfo("com.facebook.katana", 0 );

        return true;

    } catch( PackageManager.NameNotFoundException e ){

        return false;

    }

}

== Once you know that Facebook exists in your device then launch it by following

String uri = "facebook://facebook.com/inbox";

Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(uri));

startActivity(intent);

In the other way you an directly take the intent if you must call the Facebook even if the app doesn't exists.

@SuppressWarnings("unused")

private Intent isFacebookExists() {

    Intent intent;

    String uri;

    try{

        ApplicationInfo info = getPackageManager().getApplicationInfo("com.facebook.katana", 0 );

        uri = "facebook://facebook.com/inbox";

    } catch( PackageManager.NameNotFoundException e ){

        uri = "http://www.facebook.com";

    }

    intent = new Intent(Intent.ACTION_VIEW, Uri.parse(uri));

    return intent;

}

Cheers !!!