如果未安装应用程序，Facebook登录将不起作用

Question

I'm trying to implement the Facebook Login on an app that i'm developing. I followed the Facebook Developer guide and it's working! BUT, it only works if the Facebook App is installed on my smartphone. If i unninstall it or i try to run my app on a smartphone that does not have the Facebook App installed, it just crashes.

So what happens is that i tap the login button and it askes me to put in my Facebook credentials. It logs in but when i try to access the Profile like this:

Profile.getCurrentProfile().getId()

It just gives me a NullPointerException:

04-01 15:22:10.690 16758-16794/com.example.diogo.soulfiware E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
  java.lang.RuntimeException: An error occured while executing doInBackground()
      at android.os.AsyncTask$3.done(AsyncTask.java:299)
      at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
      at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
      at java.util.concurrent.FutureTask.run(FutureTask.java:239)
      at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
      at java.lang.Thread.run(Thread.java:841)
   Caused by: java.lang.NullPointerException
      at com.example.diogo.soulfiware.Fragments.FragmentSlideLogin$3$1.doInBackground(FragmentSlideLogin.java:173)
      at com.example.diogo.soulfiware.Fragments.FragmentSlideLogin$3$1.doInBackground(FragmentSlideLogin.java:158)
      at android.os.AsyncTask$2.call(AsyncTask.java:287)
      at java.util.concurrent.FutureTask.run(FutureTask.java:234)
      at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) 
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) 
      at java.lang.Thread.run(Thread.java:841) 

Funny thing is that when it crashes, if I open the app a second time, it asks me to logout as the user credentials I previously inserted and it says "Logged in as: User" and asks me to logout!

My question is: Do i really need the Facebook app to be installed in order for the login to work?

Answer 1

Facebook app is not necessarily needed as you can also proceed through web widget login. However, when you are a developer, you need to take care of key-hash pair when you generate signed apk. to keep both ways (applogin and web widget login) available, use this..

try {
    //try to open facebook app if installed. Pass the username as u_name if required
    context.getPackageManager().getPackageInfo("com.facebook.katana", 0);
    return new Intent(Intent.ACTION_VIEW, Uri.parse("fb://page/" + u_name));
} catch (Exception e) {
    //open the web login if app not installed. Pass the user id as u_id if required. 
    return new Intent(Intent.ACTION_VIEW, Uri.parse("https://www.facebook.com/" + u_id));
}