[Solved] Android OnClick and OnclickListner

Question

Why don’t you make mNsdUtils to be a member field if it should be accessed from the outside of the function?

The root cause saying mNsdUtils is null from the MainActivity.onClickDiscover() implementation.

Implement in the method itself, as the context is different throwing a null pointer exception.

A small tip for you: read the stack trace and find your source code(for your case, MainActivity.java) to locate what was the first error from bottom to up.

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.android.implicitintents.Utils.NsdUtils.discoverServices()' on a null object reference
  at com.example.android.implicitintents.MainActivity.onClickDiscoverAura(MainActivity.java:40)
  at java.lang.reflect.Method.invoke(Native Method) 
  at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
  at android.view.View.performClick(View.java:5637) 
  at android.view.View$PerformClick.run(View.java:22429) 
  at android.os.Handler.handleCallback(Handler.java:751) 
  at android.os.Handler.dispatchMessage(Handler.java:95) 
  at android.os.Looper.loop(Looper.java:154) 
  at android.app.ActivityThread.main(ActivityThread.java:6119) 
  at java.lang.reflect.Method.invoke(Native Method) 
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

This is the one you need.

at com.example.android.implicitintents.MainActivity.onClickDiscoverAura(MainActivity.java:40)

Accepted Answer