http://stackoverflow.com/questions/41922616/android-button-illegalstateexception-with-onclickmainactivity ;; https://code.google.com/p/android/issues/detail?id=225168

onClick issue

Step 1:
	File -> New -> Activity -> EmptyActivity
	
Step 2:	
	Set activity Name as "HelloWorldActivity" and click Finish
	(Don't alter any option)	

Step 3:
	Goto newly generated "HelloWorldActivity" and  define a public onClick
	method like below:
	
	public void sayHello(View v) {
    
	}

Step 4: 
	Goto activity_hello_world.xml and switch to design view.

Step 5:
	Drag & Drop the Button and click on `onClick` property in the GUI,
	the generated selection will be `sayHello (HelloWorldActivity)` 
	instead of `sayHello`