java.lang.NullPointerException: Attempt to invoke virtual method android

Question

i am a beginner in the android, and i dont know what is the problem in my code ! and i need your help, this is my code: i am trying to do a calculator = - / * ..... and i re

Answer 1

Either check you have initialized the view or may be layout not has been attached to activity.

    password = (EditText) findViewById(R.id.password);

or

setContentView(R.layour.login_screen);

Answer 2

You are initializing a local copy of variable theresult in onCreate:

TextView theresult = (TextView) findViewById(R.id.TheResult);

But in onClick you are trying to access another instance of the variable theresult which is declared outside onCreate. This one has not been initialized yet. That's why giving its giving null when you are trying to do setText.

To solve, replace the below line:

TextView theresult = (TextView) findViewById(R.id.TheResult);

with

theresult = (TextView) findViewById(R.id.TheResult);