How to simulate a button click using code?

there is a better way.

View.performClick();

http://developer.android.com/reference/android/view/View.html#performClick()

this should answer all your problems. every View inherits this function, including Button, Spinner, etc.

Just to clarify, View does not have a static performClick() method. You must call performClick() on an instance of View.
For example, you can’t just call

View.performClick();

Instead, do something like:

View myView = findViewById(R.id.myview);
myView.performClick();